Exhaust Leak Cause Lean Condition

Could it be so that case center gasket starts to leak only when engine is hot or under load? Could carbonized exhaust cause lean condition for the engine?(expansion chamber should be clean and silencer wools are recently changed) Im starting to get desperated cos there is no good reason for the engine to run so lean. Sometimes damage to the oil pan on the underside can cause minor to severe leaks. The low pressure portion of the exhaust pulse will draw outside air in. A fuel-injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air. To check for possible intake leaks, the easiest way is to start the car and go underneath it, paying close attention to any leaks from the exhaust. Yes, after-firing is through the exhaust, the vast majority of the time is cause by a lean condition. The front of the tractor actually looks dry and clean. For your header leak, have you tried a fresh gasket smeared with 22B exhaust gasket(red tube) sealer? I use it around all my tbe flanges. avoid running exhaust fans (bathroom, kitchen) if you have an un-flued or open-flued gas heater, as this may cause carbon monoxide to leak back into the room; this possibility should be tested when you have your heater serviced. The preturbo exhaust leak will likely cause more afterfire between shifts since it will cause erratic rich than lean conditions. Normally, the sensor will switch back and forth between under. This could result in fuel trim problems and a check engine light, possibly with Fuel System Rich DTCs, such as P0172 or P0175. Vacuum leaks generally cause hesitation or inconsistent component operation (ie, idle valve). maby you have an exhaust leak, but that shouldnt cause a lean condition either. One of the possible causes for the lean condition that showed up on the print out that they give you at O'Reilley Auto Parts was an exhaust leak. A leaky EGR valve can act like a vacuum leak and cause a lean misfire at idle. Page 3 of 3: Troubleshooting P0171 and P0174 (Ford 4. Leaks, no matter where the leak itself is located, will lead to a lean condition (if not recognized) and eventually to exhaust side scoring. This will cause a "Lean Misfire" condition in the engine. remember that the crankcase also has a vacuum. An EGR valve that is stuck open can result in an air-fuel mixture that is too lean. If a car has a check engine light on and has P0171 and P0174 codes stored, the most likely cause is a vacuum leak. It would depend on how bad the exhaust leak is. Contrary to popular belief, the exhaust has pulses in it from the valves opening, and will actually draw in outside air. Sorry if I wasn't clear. Can an injector leak on the return side cause a lean condition and will an LB7 go into limp mode like an LLY if the leak is bad enough I'm just trying to convince myself the truck will be fine till Monday:badidea: Any input would be appreciated. If gas filter is blocked or perhaps the gas pump pressure is reasonable, there might be higher degree of oxygen in the exhaust also. Our Universal, Direct-fit, CARB, High Performance and Diesel converter lines cover over 100,000 applications, including OBDII coverage for all 50 states and are certified in 58 countries around the world. 19) CO 2 is an indicator of combustion efficiency that peaks at or near the stoichiometric air-fuel ratios, and decreases with lean or rich air-fuel ratio. A fuel-injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective. if you find either, pull the rocker shaft off and run a leakdown test if possible. When they first come out of the engine, exhaust fumes are extremely hot, but cool gradually as they reach the tailpipe at the back of the vehicle. An intermittent may be caused by any of the following conditions: A poor connection. Since it is easier to check the intake system as opposed to the fuel system, it makes sense to smoke the intake through the ABS brake booster hose. A leak after the turbo will make you lean under vacuum and rich under boost. The ratio of air to fuel in the mixture gets skewed in favour of fuel i. A larger leak jet will allow more fuel to return to the float bowl and less to be sent to the venturi, and will decrease squirt time duration. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. A lean condition can, and likely will, manifest itself as detonation!. It alerts your system when the condition is too lean, or there’s too much oxygen in the exhaust. This can cause rough running, but may not be the cause of yours. This of course, will introduce extra oxygen into the exhaust stream, making it appear leaner than it is. In this video I will show you how to use freeze frame data and fuel trim numbers to identify a vacuum leak. 20) Air injection systems dilute the exhaust sample with O 2. Ford Expedition lean codes could caused by a leaky PCV hose. Another place to look is the PCV valve. Probably a good idea to fix the leak anyway Allan (New Zealand). Shops have simple ways to test for all of these. So, what does the code P0171 mean? The symptoms and causes will help you determine the exact issue and how to fix it. (Or maybe used your own OBD scanner to extract the car faults). 45 volts from the O2 sensor for 90 seconds or more. A lean fuel mixture would not cause a sulfur smell. Explorer, Ranger, Aerostar. Your actually running lean. EGR System. the other 2 mounts are not. If there's a hole in the exhaust close to the engine, these hot gases can. An exhaust leak can trigger a Check Engine Light due to the fact that depending on the location of the leak, the leak itself is introducing more oxygen into the exhaust gases. Damage to Other Car Parts. Then, follow. "Ultimately, a simple air leak can cause a lean condition that will cause an excess of temperature in the exhaust system, which can cause a thermal event, rendering the DPF inoperable and. Loosely connected or leaked vacuum lines and hoses can cause a vehicle to run rich. If you suspect a leaking. The O2 sensors read/ send signals depending on the amount of "unburnt" air, so if air is being sucked in the exhaust the truck will keep adding fuel trying to fix the false signal that. Possible Causes: Oil leaks, poor fuel quality. Well, I have a really unstable mixture at idle (mostly lean) and am wondering if an exhaust leak can cause this and also the hesitation that occurs at about 1000 rpm every time I start to accelerate. A fuel-injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective. If this problem goes on too long, the injector will eventually fail and cause lean conditions, which could overheat and damage your engine internals. GM, in all its infinite wisdom, uses plastic and rubber gaskets for the intake manifold and plenum gaskets. An exhaust stream is actually a series of pulses with high and low pressure zones. This indicates that there is unburned fuel in the exhaust and will send a signal to the ECM to lean the air/fuel mixture out. Vacuum Leaks- With the Toyota Rav4, one of the most common cause for the P0171 code to show is a vacuum leak. RE: Running Lean and "Melting Pistons" obanion (Automotive) 7 Sep 04 19:08 HCCI, because of the nearly instant ignition across the entire air/fuel mix, causes a VERY rapid heat and pressure rise, compared to spark ignition. I have had plenty of drama with this kx100 eating top ends and discussed it here previousl. “Ultimately, a simple air leak can cause a lean condition that will cause an excess of temperature in the exhaust system, which can cause a thermal event, rendering the DPF inoperable and. The computer throws a lean code if it is receiving less than. Oil leaking into the cylinders can cause a rough idle, misfire and fouled spark plugs. You mentioned an exhaust leak. Beyond the potential of the engine running too lean, the other thing would be if any change in sound is bothersome to you. Wet and Dry Fouling. Fuel contamination; Water, even in small amounts, can be delivered to the fuel injectors. vac lines, intake connections, filter condition, MAF condition, etc. Fixing A Rich Mixture. On the earlier engine I believe the intake manifold is called the plenum. Inspect the items that would cause both banks to operate lean. Both conditions can create poor starting and misfiring. Leaks, no matter where the leak itself is located, will lead to a lean condition (if not recognized) and eventually to exhaust side scoring. Without any exhaust leak or oxygen sensor problem, there is something else making the vehicle run lean. There are many things that can cause these trouble codes on the Cadillac Escalade. This condition is called a lean miss-fire. Lean exhaust is caused by one of two things: An. Checked compression and all but #5 were ~ 160. You can easily check that with fairly certain accuracy by using compressed air, a few rags, and a solution of water and dish soap in a squeeze bottle. I wouldn't replace the fuel injectors unless a scope test or injector balance turns up something. Be sure to check pressure at all driving modes. 4 4x4 automatic with 150k miles. Look for loose clamps, damaged donut gaskets or even holes or cracks in the pipe. Exhaust leaks before or near the HO2Ss (exhaust manifold gasket, mating gaskets, etc. A vacuum leak is most likely the cause. air is getting into the exhaust stream upstream of that O2 sensor. If any of this is wrong, Fish will set me straight, exponentionally:biggrin:. Be sure to check pressure at all driving modes. The main causes for this problem are too quick warm-up, too lean carb jetting (main jet), or too hot of a spark plug range. working on a 6 cylinder 1964 mustang with AC. There also could be some other reasons, but the air flow sensor and vacuum leaks are the most common. A leaking brake booster may also cause an engine to run badly. If the leak is on the bottom side of the inlet gasket, it will often be necessary to remove the engine from the frame to see and accurately locate the leak. I can smell a very faint exhaust smell if I'm leaning over the engine with the hood up,. code po174 - fuel system too lean cylinder bank 2. Check intake vacuum at idle, and inspect vacuum hose connections. A restriction of only 8% to 10% in a single fuel injector can lean out the fuel mixture and cause a misfire. Possible causes - Intake air leaks - Faulty front heated oxygen sensor - Ignition misfiring - Faulty fuel injectors - Exhaust gas leaks - Incorrect fuel pressure - Lack of fuel - Faulty Mass Air Flow (MAF) sensor If the HO2S indicates a rich condition, the FT values will be below 0. Discovered small exhaust leak post-cat around the area of the back seat. The Adaptive Fuel Strategy continuously monitors the fuel delivery hardware. To remedy. Although most of the time you need a mechanic's tool set and know-how to fix the problem, there are a few initial. This is a serious problem because this can cause warpage or cracking of the exhaust manifolds resulting, in exhaust leaks. Also a damaged o2 sensor/exhaust wouldn't cause a misfire unless you're running so lean your getting detonation. I see many people with their cars and bikes fiddle with these screws, and wonder why it does not help. A blocked EGR valve can cause combustion temperatures to rise, creating a lean condition and raising exhaust temperature. Yes, after-firing is through the exhaust, the vast majority of the time is cause by a lean condition. Look for an exhaust leak around the exhaust manifold, if nothing try replacing the upstream o2 sensor. F rom the Midas Mufflers website FAQ’s _____ What Causes A Backfire In Your Exhaust. GM, in all its infinite wisdom, uses plastic and rubber gaskets for the intake manifold and plenum gaskets. An exhaust leak can decrease fuel efficiency, causing your engine to work harder, and you to fill up your gas tank more frequently. Over time, and with a buildup of sludge (oil that breaks down over time due to prolonged temperature exposure), the pressure increases which can cause leaks and failures in the seal of the gaskets. Exhaust gas travels in pulses with high and low pressure zones. I am going to try the intake leak test again with propane. Because it is bolted directly to the cylinder head; it is the first line of defence from hot and dangerous gases. Lean conditions are going to score the exhaust side first. The allowance of unchecked incoming atmoshere to the exhaust will allow excessive reversion/shock wave to traverse the entire path of mix all the way to the air cleaner and lean the mix. Customer may also complain of rough idle, surging under light throttle, ignition misfire etc. So check for exhaust leaks and boost/vac leaks, then check fuel supply and front O2. Re: Clogged cats causing lean condition? #572043 11/17/05 09:15 AM. An exhaust leak near the upstream sensor can cause the downstream sensor to read a steady lean condition. Check intake vacuum at idle, and inspect vacuum hose connections. Refer to Exhaust System Inspection in Engine Exhaust. A shorter spark line would indicate a weak spark possibly due to a lean fuel condition (dirty injectors or vacuum leaks) or low compression (burned exhaust valve or bad head gasket). A leaking, burned, cracked, or stuck valve could be the cause. Your bank one oxygen sensor is the first downstream sensor. coolant leaking into the exhaust chambers would cause a gray exhaust color. if you find either, pull the rocker shaft off and run a leakdown test if possible. An exhaust leak can lead to your O2 sensors giving a faulty reading and may cause the code to trigger. Valve Guides: Excessive clearance between the valve stem and the valve guide allows the oil to leak past the gap into the cylinder. To be rich at idle you may have a fuel pressure regulator overrun from a larger pump, bad o2 sensor, or a tune so bad the fuel trims can't correct it. Air leaking ,into, your car—not out of it—can be a problem. Also, a leak condition can result in air that is not properly measured entering into the engine. Backfire is caused by combustion in the intake manifold. This will cause a "Lean Misfire" condition in the engine. It's also less likely to cause a noticeable rich condition (usually the complaint is a CEL due to a fuel trim code and maybe a mild decrease in MPG). Could an exhaust leak cause my car to die? Results 1 to 9 of 9 Thread: a leak before the O2 sensor can indeed cause the car to die. Another place to look is the PCV valve. If you have an exhaust leak behind the rear O2 sensor, it should not cause the code. Diagnosing lean oxygen sensor and fuel trim codes on your C6 Corvette. Could it be so that case center gasket starts to leak only when engine is hot or under load? Could carbonized exhaust cause lean condition for the engine?(expansion chamber should be clean and silencer wools are recently changed) Im starting to get desperated cos there is no good reason for the engine to run so lean. Engine vacuum leaks that create a lean exhaust condition. Carburetor manifold leaks can also cause frequent backfiring and popping or a power-loss that worsens over time. Exhaust Leak Cause Lean or Rich? was created by Tutti57 Does a manifold gasket leak cause the same condition as a leak at say a flex pipe? I can't wrap my head around the theory of it, whether it's sucking air in or pushing g exhaust out and how that impacts the sensor reading. exhaust silencer/joint etc leak, will cause the O2 reading to be high and all the rest to be normal. I have checked all vacuum lines, sprayed carb cleaner around MAP sensor, Intake manifold gaskets, between throttle body and manifold and around all vacuum points. Vacuum Leaks- With the Toyota Rav4, one of the most common cause for the P0171 code to show is a vacuum leak. Broken, disconnected or misrouted vacuum hoses will do the same. You may also have a carb issue with lean. Will a exhaust leak at the beginning of the pipe 2 the cylinder cause lean failure even when rich condition ? Search " " across the entire site Search " " in this forum Search " " in this discussion Advanced Search. Even the smallest leak in an intake manifold can cause a fuel trim problem. An oxygen sensor failure can lead to incorrect readings of exhaust gasses. (Or maybe used your own OBD scanner to extract the car faults). Discovered a poorly done exhaust manifold gasket job, but no indication of leaks (they broke studs, tapped in aftermarket bolts in places). Airflow sensor, fuel pressure, or things common to both banks will not trigger a single bank code. Use this Intake Leak Pressure Tester to make sure you get 100% performance from your turbo. Air leaking ,into, your car—not out of it—can be a problem. Since it is easier to check the intake system as opposed to the fuel system, it makes sense to smoke the intake through the ABS brake booster hose. Injector seals are called O rings. Checking the spark plugs for color and condition is the quickest way. Below are some tips and tricks to diagnose the most common faults /defects / failures /malfunctions that cause lean air/fuel mixtures that result in high positive fuel trim values- Small vacuum leaks; if both the short and long terms fuel trim values are higher than about 10% with the engine at idle, increase the engine speed to about 2000 RPM. An exhaust leak, a loose air boot, or carb can be your problem. Exhaust leak somewhere between the down pipe and the cylinder heads. Any condition that causes a misfire (or poor combustion) will raise HC levels. Smoke is a good way for testing for leaks on a sealed system such as EVAP, but may not be the best way to check for leaks in the intake as the smoke will simply pass through the intake and out of the exhaust. If the exaust were to have a crack before the oxygen sensor it could draw in air which would cause a false lean condition. A leaky exhaust will suck a lot of air [a huge amount!] into the cylinder and lean out the mixture. just recently the light has came on , and is staying on. blown, it will cause these problem. Loosely connected or leaked vacuum lines and hoses can cause a vehicle to run rich. You may also have a carb issue with lean. Exhaust Leaks. Long answer: Most people don't realize that an exhaust will blow out gasses, and suck in air at different times of the engines run cycle. When an engine that has computer controlled spark and fuel systems has a vacuum leak, the following events occur. Preforming a plug chop is a good way to find out if your engine is running too lean, as you will see a powdery white residue on your spark plug in the presence of a lean condition. Okay so the more oxygen in the exhaust (lean condition) the lower the voltage from the O2 sensor and the more fuel the computer calls for. I have replaced the: Water pump, 3 row radiator, 195* thermostat, 6 blade fan, fan shroud, checked timing, The car has a partly blown exhaust manifold gasket at the center 2 ports #3&4. exhaust silencer/joint etc leak, will cause the O2 reading to be high and all the rest to be normal. Fixing A Rich Mixture. Exhaust System Leaks: In this type of condition, the engine may actually be running rich of stoichiometry (14. If any of this is wrong, Fish will set me straight, exponentionally:biggrin:. This is dangerous for gasoline engines for many reasons, one of which could be deactivation of the 3-way catalyst. Could the exhaust leaking right at the head pipe cause a lean condition?. These are possible symptoms and causes: Valve Seals: Leaking valve seals will cause blue/gray exhaust smoke. These include: An inefficient catalytic converter. Can an exhaust leak cause the computer to throw an O2 sensor code? SN95 4. This results in a misfire and excess hydrocarbon (fuel) entering and burning inside of the catalytic converter. Take a look around and see if you can find the vacuum leak. Too rich and the catalyst can melt down. Ford Expedition lean codes could caused by a leaky PCV hose. I am under the impression that exhaust leaks usually make you run rich, as most lose gas mileage when you get one. Over time, and with a buildup of sludge (oil that breaks down over time due to prolonged temperature exposure), the pressure increases which can cause leaks and failures in the seal of the gaskets. 5 volts (lean signal) and over. The fuel trims show what the computer is trying to do to correct the problem. If left unattended long enough, valves burn out due to the leak, which causes rough running engine. This can be caused by poor fuel supply, vacuum leaks, or even a faulty front O2 sensor. 8n exhaust manifold leaking oil discussion in the I assumed it was all carb related, but started the post thinking that a bad manifold leak might cause a power loss as well. If compression is ok and the miss goes away at higher engine speeds, suspect a vacuum leak. I took the exhaust off of it to clean some things and noticed it doesn't have an exhaust gasket. The computer throws a lean code if it is receiving less than. Jump to Latest Follow 1 - 5 of 5 Posts an exhaust leak upstream of the O2 sensors I believe makes the sensors think there's a lean condition so it causes the engine to run richer- this would mean worse fuel economy and worse emissions. 7 parts air to 1 part fuel in the air-fuel mixture, a lean condition exists and code P0171 is triggered. A MAF that is reading too low will then result in not enough fuel being injected, and as a result the engine would be operating in a lean condition. A lean condition can, and likely will, manifest itself as detonation!. This loss of backpressure causes more fresh air to go into the cylinder, whereas with a proper tuned pipe exhaust gases would bounce back into the cylinder right before the piston blocks the port. 1v reading from the downstream sensor. This problem will be accompanied by high or low engine idle and a harder to. Unfortunately, when we have a rich or lean condition, we usually look for external engine problems first. A catalyst can not clean up CO and HC unless there is enough oxygen in the exhaust. Exhaust leak somewhere between the down pipe and the cylinder heads. Check for Any Exhaust Leaks. Road Damage or Broken Hangers. Now, I have never heard an exhaust leak sound like detonation (if this isn't detonation, then it could fool almost anyone, I promise!) but I guess it makes sense; (or not enough fuel, or anything like that that could cause detonation) then it would cause a lean condition THROUGHOUT all of the cylinders and thus show up on the wideband as a. 0 Mustang Tech: 5: Dec 16, 2019: H: Engine 94 5. This lean mixture can quickly result in a seized piston. In addition to venting toxic gases forward of the cabin where they might enter the ventilation system, exhaust leaks also affect the way the engine runs. Would an intake leak effect just 1 jug? No exhaust leak in smoke test. * Exhaust leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Exhaust gas leakage before the O2 sensors can trick them and cause code P0171. This lets outside air into the exhaust that fools the upstream O2 sensor into believing the cylinders are running lean when they are not (so called “false lean” condition). To compensate for the lean condition the engine controller signals the injectors to add more fuel in an effort to. There are lots of faults that can cause rich and lean conditions, but not so erratically. A lean fuel condition may exist in the event the engine is sucking in too considerably air and/or the fuel system is not providing adequate fuel. Set the ignition timing to specifications. during the combustion process. This can indicate a lean-or-rich condition. I have checked all vacuum lines, sprayed carb cleaner around MAP sensor, Intake manifold gaskets, between throttle body and manifold and around all vacuum points. To remedy. The codes is usually set when there is an intake leak after the air flow meter, before replacing any parts check for loose or broken hoses and intake gasket leak. Beyond the potential of the engine running too lean, the other thing would be if any change in sound is bothersome to you. Its sounds like a exhaust leak of some kind and is coming from behind the intake manifold I think? The only code I have is the p0171 system. ) Vacuum leaks can cause a lean condition and/or possibly a high idle. Another cause of blue smoke is bad valve stem seals. On Ford some models dirty air filter, and dirty or faulty air flow sensor are the cause of the problem. Honda accord element 2 4l 2003 fel pro exhaust manifold gasket set problems with your car s ler how to find and fix a vacuum leak p0420 catalytic converter system Repair SRepair SHonda Accord Exhaust ManifoldIdentify This Oil Leak Drive Accord Honda ForumsRepair SRepair SHelp Water Leaking From Bolt In Exhaust Manifold Honda TechVacuum Leaks Read More ». Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. A vacuum leak and exhaust leak. Does an exhaust leak create a lean or rich condition? What effect does this have on catalyst efficiency? www. Ford TSB 04-17-4 details procedures for checking fuel trim and looking for vacuum leaks. Conclusion:. If it is a cracked exhaust manifold, then yes that may be the problem. If compression is ok and the miss goes away at higher engine speeds, suspect a vacuum leak. Most Common Cause of a Freon Leak in Central Air Units. A lean condition can, and likely will, manifest itself as detonation!. When in “closed loop,” the ECU can detect a lean, or rich, condition and add/subtract fuel to compensate, bringing the observed AFR back in line. (they say it is hard to get to so the labor charge is high). Sometimes, the engine gets the supply of fuel more than it can burn. Then I will be using water to locate the specific area of the vacuum leak. Intake leaks can overwork or even destroy a turbo and cause a rich or lean condition in the engine. A MAF that is reading too low will then result in not enough fuel being injected, and as a result the engine would be operating in a lean condition. When this is done, check to see of if the vacuum leak is reported by the downstream sensor. Gray or Blue Smoke from Diesel Exhaust. 1v reading from the downstream sensor. 5 volts (lean signal) and over. When an exhaust leak is present, the ECU can detect a false lean signal and respond incorrectly, adding fuel in an attempt to remedy the problem, but further exacerbate it. I agree with robert. Rubbed through wire insulation. It will read this as lean. Sorry if I wasn't clear. There are many other causes, a leak in the intake, leak in exhaust before the O2 sensors, cracked or disconnected vacuum hoses, fuel regulator, fuel pump, clogged fuel lines etc. Still had same problem. Re: Lean Runaway Condition After Carb Rebuild I left the intake manifold in place when I did the leak down test. An exhaust system leak that may not be audible but can set this code. One of the possible causes for the lean condition that showed up on the print out that they give you at O'Reilley Auto Parts was an exhaust leak. The most common cause is the crush washer seal in the exhaust port of the cylinder. Any leak forward of the oxygen sensors can cause a false reading and a fault code to be set. What would cause popping through exhaust? Reving my motor steady at around 2400 rpm or cruising I get an intermit slight popping sound out of the exhaust. When your engine light comes on because of a weakness or failure in this system, you most likely won’t notice the car driving any differently. A leak announces its presence with a hissing sound. I know an intake leak or vacuum leak can cause a lean condition. Loosely connected or leaked vacuum lines and hoses can cause a vehicle to run rich. Then, follow. Although most of the time you need a mechanic's tool set and know-how to fix the problem, there are a few initial. Now that we know the general condition of the engine, locating the cause of the low speed miss is quick and easy. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits. Im going to disconnect the 02 sensors for now and order a pcv 5. The OBDII trouble code P0171 - System Too Lean (Bank 1) means that the engine air-fuel mixture is too lean, or there is too much air and too little fuel. Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). To remedy. An exhaust stream is actually a series of pulses with high and low pressure zones. The internal cylinder condition is just as important, …. ’ When an engine runs rich, it burns fuel slowly, causing the extra air to forcefully burn the unburned fuel and spit out when the exhaust valve opens. Just pull the plug and look for a lean condition and possible mechanical damaqe. Pressure test. But to make the car run really really bad it would have to fairly large leak and you would probably hear it. 7) Check idle solenoid, especially for power/ground, replace solenoid if necessary. And always check for after- market modifications. Either way, a lean condition is an indicator of imbalance. Our technicians tell us the left valve cover gasket, upper intake gaskets, vacuum line, and bolts may need to be replaced with updated parts to correct this concern. CAUSE 1: PCV Tube's rubber elbow (where it connects to the intake manifold) is torn open and causing a major vacuum leak. "Can an exhaust leak cause a misfire?" I've encountered a few cases of multiple cylinder misfires that were caused by an exhaust manifold leak. Backfire conditions are caused by lean conditions and or fresh air getting into the exhaust caused by a leak at a connection, for the exhaust leak test, start the engine and have a friend block off both outlets of the mufflers using a couple rags in each hand, if there is a leak you should be able to hear the air pushing past the leaking connection. A bad vacuum leak can lean out the mixture enough to cause an engine backfire. Third issue would be idle speed, which can be manipulated with a hot idle compensator from a 289-2V (it plumbs in line with the PCV valve to create a controlled vacuum leak when underhood temps get hot, which raises idle) or plumbing a DVCV (distributor vacuum control valve) which threads into the later model (IIRC, '70+) thermostat housing, in which you tap the center port into manifold vacuum, cap the top port, and run the bottom port into an aquarium air pump filter. From my understanding its a lean condition somewhere (possible vaccumm leak) and the ECU dumbs fuel to compensate. “Ultimately, a simple air leak can cause a lean condition that will cause an excess of temperature in the exhaust system, which can cause a thermal event, rendering the DPF inoperable and. Without any exhaust leak or oxygen sensor problem, there is something else making the vehicle run lean. Engine Performance Diagnostics chapter 1 pages 9-12. I've read before that in a stock application that if there is a leak at the h-pipe to header connection that air can be drawn in and cause the computer to make adjustments thinking it's lean (or something like that. Intake manifold air leaks will suck in air, not expel it. An exhaust leak near the upstream sensor can cause the downstream sensor to read a steady lean condition. Lean burn occurs when there's too much air in the combustion chamber. The oxygen sensor is in the exhaust stream somewhere downstream of the leak. A lean condition due to an intake manifold air leak can cause backfiring. A restriction of only 8% to 10% in a single fuel injector can lean out the fuel mixture and cause a misfire. Airflow sensor, fuel pressure, or things common to both banks will not trigger a single bank code. Look for an exhaust leak around the exhaust manifold, if nothing try replacing the upstream o2 sensor. then i came upon a very old article taking about the myth of burnt Valves and exhaust leaks. CAUSE 1: PCV Tube's rubber elbow (where it connects to the intake manifold) is torn open and causing a major vacuum leak. Vacuum leaks, torn intake boots, compromised gaskets, or even just the intake manifold bolts are loose are all possibilities. The P0171 or P0174 misfire code is set usually caused by lean mixture, it can means the engine is getting too much air, or engine is not getting enough fuel, possibly through a leaky EGR valve or a vacuum leak. Those codes do NOT mean the O2 sensors are bad, it means a lean condition has been detected. This symptom is most noticeable at idle. Oil Leak Troubleshooting in Exhaust Pipe. Lean conditions are going to score the exhaust side first. Depends on where the leak is. Unfortunately, when we have a rich or lean condition, we usually look for external engine problems first. Look for an exhaust leak around the exhaust manifold, if nothing try replacing the upstream o2 sensor. Fuel Pressure could also cause a lean condition. When the STFT reaches the limit of its adjustment it will cause corresponding decrease or increase to the Long Term Fuel Trim. I've also had an exhaust smell in the cabin, on colder days I would just switch on recirculate and the windows would be closed, didn't really seem to get in the car. Here is a good example of a 1987 Honda Shadow VT700C that is running lean. However this occurs only on cylinders with bridged exhaust ports. 0bar unit, the same amount of fuel is delivered resulting in a more lean condition. CAUSE 2: Intake manifold gaskets or plenum gaskets are leaking vacuum. The computer throws a lean code if it is receiving less than. This causes a lean misfire, where the combustion process ends too soon, sending unburned gas into the exhaust. ) The symptoms: On a cold start, it always dies at least once. Pressure test. Dirty air filters and leaky turbocharger oil seals are relatively common. Re: Exhaust leak causing a miss? « Reply #24 on: Dec 05, 2010, 10:29:44 AM » weak ignition could cause lean condition i would suggest you get a hayne manual has all info on testing your sensors and ignition componets. An exhaust system leak really screws up the P0420 testing routing. Look for an exhaust leak around the exhaust manifold, if nothing try replacing the upstream o2 sensor. Then the oxygen content in the exhaust drops (because it is being used up in the combustion process), and the voltage increases (rich condition) and the process repeats, for as long as the car is running, hundreds of times a minute. Codes P0171 & P0174 (Too lean bank 1 & Too lean bank 2) 13 Answers. Another cause of misfiring is a weak fuel injector a condition that is referred to as “lean misfire” and occurs because there is no enough fuel in the combustion chamber. Also a damaged o2 sensor/exhaust wouldn't cause a misfire unless you're running so lean your getting detonation. A restriction of only 8% to 10% in a single fuel injector can lean out the fuel mixture and cause a misfire. Over time, the fumes leaking from a cracked exhaust pipe will damage surrounding components, and could even cause a fire. If there is too much fuel mixed with the air, the engine will have a rich condition. animals and children at play are three of the leading causes of damage to an air conditioning system. Engine vacuum leaks that create a lean exhaust condition. This is intended for one use only. I ran the codes and the 'running lean" codes came up. A low voltage (lean) reading may indicate a bad O2 sensor, a vacuum leak, or a condition that allows unburned oxygen to enter the exhaust. SU & Zenith-Stromberg Fuel and Carburetor Symptoms & Diagnosis Before adjusting the carburetors, verify that the following items have been checked for proper operation. Vacuum or crankcase ventilation system leaks can cause a lean condition or possibly a high idle. * Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle. manifold/ down pipe, then a diluted exhaust gas will be monitored by the lambda. If a valve leak is significant, engine performance will deteriorate and/or noise and vibration will increase significantly. Blue smoke is coming from my exhaust This is a definite indication that this engine is burning oil. This is intended for one use only. He said its an extreme lean condition causing the exhaust to heat up and burn the coating on the heat sheilds. Wet fouling (bottom) has a wet, sometimes oily appearance. Bikes with CV style carburetors may be self adjusting to atmospheric pressures. To determine if the lean condition is the result of a vacuum leak, bring the engine up to about 2,000 RPM. I will say that an exhaust leak could be causing the lean code. A leaky EGR valve can act like a vacuum leak and cause a lean misfire at idle. If the exaust were to have a crack before the oxygen sensor it could draw in air which would cause a false lean condition. Pressure test. Other possibilities are a bad vacuum leak. 02 Wrangler Napa high milage 10w40 It would cause a lean condition. When an exhaust leak is present, the ECU can detect. The EVAP system is a closed system that captures fuel tank vapors and prevents them from escaping into the atmosphere. An intake leak would certainly give you lean condition symptoms. Conclusion:. Exhaust leaks can cause oxygen sensor to send a false lean reading. A shorter spark line would indicate a weak spark possibly due to a lean fuel condition (dirty injectors or vacuum leaks) or low compression (burned exhaust valve or bad head gasket). Fixing A Rich Mixture. Checking the spark plugs for color and condition is the quickest way. * Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle. Some factors that cause random misfires will set code P0300 such as low fuel pressure or dirty fuel injectors. I also had a slight hesitation when cruising at around that rpm then feathering the gas. A lean fuel condition may exist in the event the engine is sucking in too considerably air and/or the fuel system is not providing adequate fuel. I had a 'tapping' sound (sounded a lot like loose valves) that was progressively getting worse prior to changing plugs. If any of this is wrong, Fish will set me straight, exponentionally:biggrin:. air is getting into the exhaust stream upstream of that O2 sensor. GM, in all its infinite wisdom, uses plastic and rubber gaskets for the intake manifold and plenum gaskets. P0174 - Bank 2 too lean. A very hot exhaust will heat up the front 02 depending where it is and skew its reading, pretty sure in the lean direction. if a leakdown isn't something you're equipped to do, run a compression test and see if you've got a dead hole. As a result, The faulty sensor can cause a too rich or too lean condition. If the fuel mixture becomes too lean, "lean misfire" may occur as the load on the engine increases. Can an injector leak on the return side cause a lean condition and will an LB7 go into limp mode like an LLY if the leak is bad enough I'm just trying to convince myself the truck will be fine till Monday:badidea: Any input would be appreciated. Did you check to see if you have an exhaust leak between the header and muffler or a loose head flange? Introducing fresh air into the exhaust beyond the valve can also cause dec e l popping, of which I was reminded on the DynoJet website below. If the code clears I would go to rockauto and get the egr pipe they're not that much and it would be a permanent fix. Over time, and with a buildup of sludge (oil that breaks down over time due to prolonged temperature exposure), the pressure increases which can cause leaks and failures in the seal of the gaskets. This symptom is most noticeable at idle. this will produce steam and free Ox that the O2 will pick up on. I heard that, among other causes, an exhaust leak can cause a MIL P0420. Often a roof can be in perfect condition but because the wind drives the rain across and upwards it can get under the eave and under the roof. Common causes of backfires are: Wankel rotary engines are known for leaking oil into the exhaust system which causes backfire. A lean condition can, and likely will, manifest itself as detonation!. Re: Lean Runaway Condition After Carb Rebuild I left the intake manifold in place when I did the leak down test. Compression tests averaged dry-(180, 180, 90, 90), and with oil-(200, 200, 180, 180) over two test each (wide open throttle, all spark plugs removed, each. So the air could make its way back a few inches to the exhaust valve. Re: Can exhaust leak cause P0171 and P0174 The "plenum" or plenum duct IS the boot on the 2000+ engines. Another place to look is the PCV valve. This may cause flooding, bogging, and stalling. Check for head gasket leak and did a block test and all was good. The allowance of unchecked incoming atmoshere to the exhaust will allow excessive reversion/shock wave to traverse the entire path of mix all the way to the air cleaner and lean the mix. A shorter spark line would indicate a weak spark possibly due to a lean fuel condition (dirty injectors or vacuum leaks) or low compression (burned exhaust valve or bad head gasket). An exhaust leak can decrease fuel efficiency, causing your engine to work harder, and you to fill up your gas tank more frequently. This fault is both common and a clear indication of a sticky HO 2 S. They said after the car passed diagnosis except for the lean conditions, and told me they found an bad manifold gaskets. Re: Can exhaust leak cause P0171 and P0174 The "plenum" or plenum duct IS the boot on the 2000+ engines. Together with the unburned fuel in the exhaust system and an open exhaust, the sparking results in the. If you are pressurizing the exhaust system, that would still push out exhaust. The upstream HO 2. It is going to cost me about $500. Bank 1 and Bank 2 Lean?? the manual says an exhaust leak could cause it. Re: Lean Runaway Condition After Carb Rebuild I left the intake manifold in place when I did the leak down test. If the mass airflow sensor is causing the lean condition, cleaning it may help, but usually, it will need to be replaced. Check the engine compression. this will produce steam and free Ox that the O2 will pick up on. Try wrapping that egr pipe and seal the exhaust leak. Bikes with CV style carburetors may be self adjusting to atmospheric pressures. Because it is bolted directly to the cylinder head; it is the first line of defence from hot and dangerous gases. I'm going to address the issue that has so far been overlooked. The main causes for this problem are too quick warm-up, too lean carb jetting (main jet), or too hot of a spark plug range. Water contamination will cause a lean condition. The internal cylinder condition is just as important, […]. Sorry if I wasn't clear. You may also have a carb issue with lean. 5 NA OB with 105,000 miles and I've put new plugs & wires (also did the head gaskets & timing belt). A catalyst can not clean up NOx unless the level of oxygen in the exhaust is very low. This condition is known as ‘running rich. I'm going to respectfully disagree on the exhaust leak/crack. Sometimes damage to the oil pan on the underside can cause minor to severe leaks. (I think this is unrelated. Causes of Excessive Exhaust Emissions: As a general rule, excessive HC, CO, and NOx levels are most often caused by the following conditions: Excessive HC results from ignition misfire or misfire due to excessively lean or rich air/fuel mixtures ; Excessive CO results from rich air/fuel mixtures. Another place to look is the PCV valve. As a result, The faulty sensor can cause a too rich or too lean condition. when its not leaned out or misfiring or is it doing one of them To gain more insight as to how an exhaust-leak can cause a temporary lean condition INSIDE THE EXHAUST! (and not inside the engine), try. When there are more than 14. even w/o a fuel tuner. It was suggested to me, on here, to try to clean up carbon deposits on the top of the pistons. 7:1 air / fuel ratio) because the fuel control system is adding fuel to compensate for a perceived (not actual) lean condition. The smallest leak will have a big impact on performance,. My 700 sportsman had a small leak and would glow red after a short ride. What would cause popping through exhaust? Reving my motor steady at around 2400 rpm or cruising I get an intermit slight popping sound out of the exhaust. If a main vacuum hose such as the power brake booster feed line has broken or failing off it will cause a lean backfire due to the additional air allowed into the engine intake manifold. The exhaust gas recirculation (EGR) valve sends some of the engine's exhaust gases back through the intake system to lower the vehicle's emissions. A leak in the exhaust system before the O2 sensor will also cause incorrect readings. This results in a misfire and excess hydrocarbon (fuel) entering and burning inside of the catalytic converter. 7:1 air / fuel ratio) because the fuel control system is adding fuel to compensate for a perceived (not actual) lean condition. You can probably reuse them if they are in good condition. Best Answer: YES. Avoid long periods of idling as this can cause discoloration. during the combustion process. Exhaust leaks before or near the HO2Ss (exhaust manifold gasket, mating gaskets, etc. Cold Start-Up Misfires - 2003 Chevrolet Tahoe 5. Water contamination can cause a lean condition. Since O2 and A/F sensors are located in the exhaust stream, any leakage upstream or even nearby may be misinterpreted as a lean condition because outside air is pulled into the leaking exhaust pipe during the low-pressure phase between firing events. There are five factors that could cause a lean mixture to occur. Problem: The EGR valve leaks causing exhaust gases to enter the combustion chamber at all times, therefore creating a lean air/fuel mixture. A smaller leak jet will restrict the amount of fuel going back into the float bowl, and will force more fuel up into the venturi. would you rule out the exhaust leak being the cause of this problem? Girls and Money and New Clothes. Lean is on intake side not exhaust. If I remember correctly (this was about 10 years ago), the car just didn't want to run smooth. the other 2 mounts are not. These codes are set by the car's computer when it sees too much oxygen in the exhaust. Wet and Dry Fouling. I finally took my car to the shop to repair a lean condition causing very rough idle and poor acceleration. Contrary to popular belief, the exhaust has pulses in it from the valves opening, and will actually draw in outside air. Ford Expedition lean codes could caused by a leaky PCV hose. Step 5: Check for Vacuum Leaks. If you are leaking exhaust through a crack, that wouldn't introduce new air into the system. CAUSE 1: PCV Tube's rubber elbow (where it connects to the intake manifold) is torn open and causing a major vacuum leak. Can an exhaust leak pre turbo cause a stutter like affect or something similar? I think its a leak at one of the flanges pre turbo, it seems that once the exhaust heats up and expands at one of these flanges the leak stops and so does the stutter, its only on start up when the exhaust is cold, and there is no boost/vacuum leaks. You can get the Hondabond that american opel mentioned at a Honda automobile dealership parts counter. If okay, check for a misfiring cylinder, a burned exhaust valve that is leaking compression, or a leaky exhaust manifold gasket. Vacuum Leaks- With the Cadillac Escalade, the most common cause for the P0174 or P0171 code to show is a vacuum leak. A leak between the exhaust manifold and head is sure close enough, and maybe the outlet of the manifold if it's compact. Even the smallest leak in an intake manifold can cause a fuel trim problem. Water contamination can cause a lean condition. In addition, if the fuel level is set too high in the float chamber, a rich mixture will result. Troubleshooting Lean Condition: 1. The lean condition can be caused by a vacuum leak, which introduces more air into the air-fuel mixture, or by a weak fuel system, which does not input enough fuel into the air-fuel mixture. What you get is a venturi effect. The idle mixture screws will only effect the running at idle. It alerts your system when the condition is too lean, or there's too much oxygen in the exhaust. Do not replace O2 sensors when you have those codes. When STFT hits its limit (-25%), the HO 2 S finally drops, and is then stuck lean until STFT is able to climb back up to normal levels. Let’s talk about the different colors of diesel exhaust smoke, their causes and solutions. Lean conditions are going to score the exhaust side first. If the oxygen in the exhaust gas decreases, the. A leaking brake booster may also cause an engine to run badly. As a result, The faulty sensor can cause a too rich or too lean condition. Other possible causes of blue exhaust smoke include: piston wear, worn valve seals, a dirty or non-functioning PCV valve, worn piston rings, an intake manifold gasket leak, worn engine oil seals and possibly even head gasket failure. Even with a good flange and o-ring set, if the flange on the pipe isn't perfectly round you can have a leak, but silicone will cure that problem. Sorry if I wasn't clear. Would an intake leak effect just 1 jug? No exhaust leak in smoke test. You may think of lean as meaning too much air for the amount of fuel or as not enough fuel for the amount of air. So your car's CEL (always check Engine Light) is on and also you had the codes scanned at a local parts shop. There are many other causes, a leak in the intake, leak in exhaust before the O2 sensors, cracked or disconnected vacuum hoses, fuel regulator, fuel pump, clogged fuel lines etc. An exhaust leak can cause a check engine light for a lean condition but will not usually cause a MAP sensor code. Third issue would be idle speed, which can be manipulated with a hot idle compensator from a 289-2V (it plumbs in line with the PCV valve to create a controlled vacuum leak when underhood temps get hot, which raises idle) or plumbing a DVCV (distributor vacuum control valve) which threads into the later model (IIRC, '70+) thermostat housing, in which you tap the center port into manifold vacuum, cap the top port, and run the bottom port into an aquarium air pump filter. Since it is easier to check the intake system as opposed to the fuel system, it makes sense to smoke the intake through the ABS brake booster hose. Our technicians tell us the left valve cover gasket, upper intake gaskets, vacuum line, and bolts may need to be replaced with updated parts to correct this concern. Trying to tune my procharged Trans am and something I am seeing when the car warms up (190-210) is that my STFT's on the drivers side is around 50 and passenger is high too (to be honest I can't remember) before I post a log/scan I was wanting to get some ideas on what may be causing this? From my understanding its a lean condition somewhere (possible vaccumm leak) and the ECU dumbs fuel to. If DTC 174 is also set indicates both banks of the engine are operating lean. A lean condition may be present during high fuel demand due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe. Conclusion:. Your mechanic can check for vacuum leaks and test the mass airflow sensor with a scan tool. As a result, The faulty sensor can cause a too rich or too lean condition. The thinking was the pre-detonation was due to carbon covered piston tops. Refer to Exhaust System Inspection in Engine Exhaust. If the lean condition is gone then replace the MAF sensor. 1 and getting a lean condition. Make sure there are no exhaust leaks at the junction of the exhaust pipes and cylinder heads. One quick test for leakage, is to turn the engine off and press the brake pedal. * Exhaust leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Turbulence can cause an uneven distribution of the fuel droplets before ignition and cause a misfire. Vacuum leaks generally cause hesitation or inconsistent component operation (ie, idle valve). Probably a good idea to fix the leak anyway Allan (New Zealand). The additional air leaking into the exhaust may cause the oxygen sensor to report a lean condition and the ECU will inject more fuel. The exhaust seals are usually good for 2-3 times usage. Excess oxygen in the exhaust indicates a failure to achieve that goal and is generally the sign of a lean condition. If the oxygen in the exhaust gas decreases, the. Check also for cold exhaust leaks. Probable Cause; P0171: Fuel trim (FT) system too lean, bank 1: Intake/exhaust leak, AIR system, MAFNAF sensor, fuel pressure/pump, injector(s), HO2S If the engine is in good condition, and there are no exhaust leaks, engine vacuum leaks, or misfires present, all sensors are working as designed, and all oxygen sensors and catalytic converter. Perform a leak-down test to make sure the cooling system holds system pressure (check pressure cap for exact pressure) for 15 minutes. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. exhaust side. Rubbed through wire insulation. General vacuum leaks will do it too, like upper/lower leaks. vacuum and exhaust leaks it puts all the strain on the driver side one and causes it to wear out faster. Diagnosing lean oxygen sensor and fuel trim codes on your C6 Corvette. Water contamination will cause a lean condition. Fuel System A malfunctioning fuel system can reduce the amount of fuel coming into the engine, causing a run lean condition. Any leak forward of the oxygen sensors can cause a false reading and a fault code to be set. Over time, the fumes leaking from a cracked exhaust pipe will damage surrounding components, and could even cause a fire. In addition to venting toxic gases forward of the cabin where they might enter the ventilation system, exhaust leaks also affect the way the engine runs. I am going to try the intake leak test again with propane. Check out all the maintenance parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. CAUSE 2: Intake manifold gaskets or plenum gaskets are leaking vacuum. if a leakdown isn't something you're equipped to do, run a compression test and see if you've got a dead hole. If the exhaust leak is in the back of the car, well-past the cats & O2 sensor, would it still cause it to throw the code? I have a 2007 2. Also, a leaking exhaust manifold can cause a lean condition or rich condition which causes driveablity symptoms such as running rough. The thinking was the pre-detonation was due to carbon covered piston tops. At idle, intake manifold vacuum is high and each cylinder receives a rarified air\fuel charge. Our technicians tell us the left valve cover gasket, upper intake gaskets, vacuum line, and bolts may need to be replaced with updated parts to correct this concern. An exhaust leak can lead to your O2 sensors giving a faulty reading and may cause the code to trigger. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits. Inspect the items that would cause both banks to operate lean. That code is usually caused by an exhaust leak causing the mix to lean out before it gets to the O2 sensors, or, the O2 sensors have gone wonky, but that usually results in an Oxygen sensor circuit low/high voltage code. Catalytic converters can only function efficiently if the engine is operating properly and the exhaust system is leak-free. What you get is a venturi effect. If you had one, you should have picked it up with your test. Jump to Latest Follow 1 - 5 of 5 Posts an exhaust leak upstream of the O2 sensors I believe makes the sensors think there's a lean condition so it causes the engine to run richer- this would mean worse fuel economy and worse emissions. Exhaust leaks, especially near the sensor can pull in air and cause a false lean reading. Checked compression and all but #5 were ~ 160. Turbulence can cause an uneven distribution of the fuel droplets before ignition and cause a misfire. If you suspect a leaking. See all 7 photos With the engine not running, to help find any exhaust leaks. An exhaust leak near the front O2 sensor could cause the sensor to detect a lean condition, causing the ECM to richen the A/F - Air/Fuel mixture = reduced gas mileage. 5 volts (lean signal) and over. Such a swing in A/F ratio is a sign that an upstream or control sensor is faulty. One of the possible causes for the lean condition that showed up on the print out that they give you at O'Reilley Auto Parts was an exhaust leak. i have a 1999 4runner 3. As you may know the oxygen sensors which are part of your emissions system read exhaust gases to determine whether or not the appropriate amount of oxygen is present in. As a result, the PCM miscalculates the amount of the injected fuel, and the engine runs "lean". Look for loose clamps, damaged donut gaskets or even holes or cracks in the pipe. A lot of the above is good info, but nobody mentioned to you that a leak in your exhaust, either at the head or the muffler clamps could becausing your popping. This causes the actual air flow to be higher than the mass air flow sensor measures. Sometimes, the engine gets the supply of fuel more than it can burn. Either way, a lean condition is an indicator of imbalance. have plenty of ventilation – ventilation is very important as it allows fresh air to come in and fumes to go out. You may think of lean as meaning too much air for the amount of fuel or as not enough fuel for the amount of air. If the rpm change you may have a leak, also keep something around in case of fire. The engine's intake system depends on being completely sealed and free from leaks. Then, follow. To compensate for the lean condition the engine controller signals the injectors to add more fuel in an effort to. Bike only has stage one xbow exhaust on them. Does an exhaust leak create a lean or rich condition? What effect does this have on catalyst efficiency? www. This causes a big vacuum leak that permits extra "false air" to enter that cylinder resulting in a very lean condition. This is especially true for direct injection vehicles with the lean air/fuel ratios. When in "closed loop," the ECU can detect a lean, or rich, condition and add/subtract fuel to compensate, bringing the observed AFR back in line. Backfire conditions are caused by lean conditions and or fresh air getting into the exhaust caused by a leak at a connection, for the exhaust leak test, start the engine and have a friend block off both outlets of the mufflers using a couple rags in each hand, if there is a leak you should be able to hear the air pushing past the leaking connection. Found no vaccum leaks, not intake leaks, propane test around intake did nothing to idle. Absolutely, a leaking exhaust manifold can cause those codes. However this occurs only on cylinders with bridged exhaust ports. So check for exhaust leaks and boost/vac leaks, then check fuel supply and front O2. extra oxygen vs stale air = lean burn.

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