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Engine backfire
What are the most common causes and remedies for engine backfire?
(At least, I think backfire is the correct term for my problem... it is an occasional loud 'bang' as if from gunfire, which seems to emanate from near the catalytic converters under my floorboard rather than up in the engine compartment.) Anyway, assuming that I am using the correct term... I have a jeep with a fuel injected chevy engine, and it backfires from time to time. Every occurence is when the engine is revving down (e.g., I put the clutch in.) However, beyond that, there is no rhyme or reason... sometimes it will happen 3 times in an hour, other times it might go weeks with no backfire. I can't detect any other common factor besides revving down (e.g., it happens regardless of whether the engine is hot or cold, what gas I'm running, etc.) |
Re: Engine backfire
>What are the most common causes and remedies for engine backfire?
Too much oxygen in exhaust, letting unburned HCs ignite prior to catalysis. Bad EGR, O2 sensor, hole in exhaust system prior to catalytic convertor, or maybe other bits & pieces of anti-pollution crap! Had a REAL problem with this in my '84 Isuzu Trooper II 1.9L 4-spd. If it hadn't eventually been fixed under 50k pollution crap warranty, I would have taken a wrench to someone's noggin! Three very frustrating, indecisive trips to dealer required, followed by a nastygram to dealership owner finally got it straight! Best of luck! Paul B. 01 XJ |
Re: Engine backfire
>What are the most common causes and remedies for engine backfire?
Too much oxygen in exhaust, letting unburned HCs ignite prior to catalysis. Bad EGR, O2 sensor, hole in exhaust system prior to catalytic convertor, or maybe other bits & pieces of anti-pollution crap! Had a REAL problem with this in my '84 Isuzu Trooper II 1.9L 4-spd. If it hadn't eventually been fixed under 50k pollution crap warranty, I would have taken a wrench to someone's noggin! Three very frustrating, indecisive trips to dealer required, followed by a nastygram to dealership owner finally got it straight! Best of luck! Paul B. 01 XJ |
Re: Engine backfire
>What are the most common causes and remedies for engine backfire?
Too much oxygen in exhaust, letting unburned HCs ignite prior to catalysis. Bad EGR, O2 sensor, hole in exhaust system prior to catalytic convertor, or maybe other bits & pieces of anti-pollution crap! Had a REAL problem with this in my '84 Isuzu Trooper II 1.9L 4-spd. If it hadn't eventually been fixed under 50k pollution crap warranty, I would have taken a wrench to someone's noggin! Three very frustrating, indecisive trips to dealer required, followed by a nastygram to dealership owner finally got it straight! Best of luck! Paul B. 01 XJ |
Re: Engine backfire
This is what Chris (c) wrote in one of my threads regarding a leak down
test. Note the reference to an occasional popping: "It is most common for racers to use leakdown to test the condition of their engine, but there is much more you can diagnose with it. An engine can show relatively good compression numbers and still have a problem, but not necessarily all the time. For instance, a head gasket that has started to seep (and will fail eventually) doesn't always get detected with a compression test due to the short time the cylinder sees pressure while cranking the engine. A leakdown test will find that seeping gasket if the air is left on long enough. I have also detected a bad exhaust valve with a leakdown that wasn't detected with a compression test. This particular engine ran fine, except for an very infrequent pop out the exhaust pipe. The leakdown showed it was only holding 40% as compared to 80-85 for the other cylinders. When we tore the heads off, there was an exhaust valve with a small crack from the stem out to the valve seat. I would bet that eventually this valve would have broke and caused some serious damage. It was on a Dodge 440 that got driven pretty hard." Hope this helps, Bill <ezeppelin@msn.com> wrote in message news:fa415237.0402171619.552c2597@posting.google.c om... > What are the most common causes and remedies for engine backfire? > > (At least, I think backfire is the correct term for my problem... it > is an occasional loud 'bang' as if from gunfire, which seems to > emanate from near the catalytic converters under my floorboard rather > than up in the engine compartment.) > > Anyway, assuming that I am using the correct term... I have a jeep > with a fuel injected chevy engine, and it backfires from time to > time. Every occurence is when the engine is revving down (e.g., I put > the clutch in.) However, beyond that, there is no rhyme or reason... > sometimes it will happen 3 times in an hour, other times it might go > weeks with no backfire. I can't detect any other common factor > besides revving down (e.g., it happens regardless of whether the > engine is hot or cold, what gas I'm running, etc.) |
Re: Engine backfire
This is what Chris (c) wrote in one of my threads regarding a leak down
test. Note the reference to an occasional popping: "It is most common for racers to use leakdown to test the condition of their engine, but there is much more you can diagnose with it. An engine can show relatively good compression numbers and still have a problem, but not necessarily all the time. For instance, a head gasket that has started to seep (and will fail eventually) doesn't always get detected with a compression test due to the short time the cylinder sees pressure while cranking the engine. A leakdown test will find that seeping gasket if the air is left on long enough. I have also detected a bad exhaust valve with a leakdown that wasn't detected with a compression test. This particular engine ran fine, except for an very infrequent pop out the exhaust pipe. The leakdown showed it was only holding 40% as compared to 80-85 for the other cylinders. When we tore the heads off, there was an exhaust valve with a small crack from the stem out to the valve seat. I would bet that eventually this valve would have broke and caused some serious damage. It was on a Dodge 440 that got driven pretty hard." Hope this helps, Bill <ezeppelin@msn.com> wrote in message news:fa415237.0402171619.552c2597@posting.google.c om... > What are the most common causes and remedies for engine backfire? > > (At least, I think backfire is the correct term for my problem... it > is an occasional loud 'bang' as if from gunfire, which seems to > emanate from near the catalytic converters under my floorboard rather > than up in the engine compartment.) > > Anyway, assuming that I am using the correct term... I have a jeep > with a fuel injected chevy engine, and it backfires from time to > time. Every occurence is when the engine is revving down (e.g., I put > the clutch in.) However, beyond that, there is no rhyme or reason... > sometimes it will happen 3 times in an hour, other times it might go > weeks with no backfire. I can't detect any other common factor > besides revving down (e.g., it happens regardless of whether the > engine is hot or cold, what gas I'm running, etc.) |
Re: Engine backfire
This is what Chris (c) wrote in one of my threads regarding a leak down
test. Note the reference to an occasional popping: "It is most common for racers to use leakdown to test the condition of their engine, but there is much more you can diagnose with it. An engine can show relatively good compression numbers and still have a problem, but not necessarily all the time. For instance, a head gasket that has started to seep (and will fail eventually) doesn't always get detected with a compression test due to the short time the cylinder sees pressure while cranking the engine. A leakdown test will find that seeping gasket if the air is left on long enough. I have also detected a bad exhaust valve with a leakdown that wasn't detected with a compression test. This particular engine ran fine, except for an very infrequent pop out the exhaust pipe. The leakdown showed it was only holding 40% as compared to 80-85 for the other cylinders. When we tore the heads off, there was an exhaust valve with a small crack from the stem out to the valve seat. I would bet that eventually this valve would have broke and caused some serious damage. It was on a Dodge 440 that got driven pretty hard." Hope this helps, Bill <ezeppelin@msn.com> wrote in message news:fa415237.0402171619.552c2597@posting.google.c om... > What are the most common causes and remedies for engine backfire? > > (At least, I think backfire is the correct term for my problem... it > is an occasional loud 'bang' as if from gunfire, which seems to > emanate from near the catalytic converters under my floorboard rather > than up in the engine compartment.) > > Anyway, assuming that I am using the correct term... I have a jeep > with a fuel injected chevy engine, and it backfires from time to > time. Every occurence is when the engine is revving down (e.g., I put > the clutch in.) However, beyond that, there is no rhyme or reason... > sometimes it will happen 3 times in an hour, other times it might go > weeks with no backfire. I can't detect any other common factor > besides revving down (e.g., it happens regardless of whether the > engine is hot or cold, what gas I'm running, etc.) |
Re: Engine backfire
You may have a gap or hole in the pipe before the oxygen sensor. It will
eventually burn out your cat converter also and you'll have to replace it to make it through emmisions. Nick <ezeppelin@msn.com> wrote in message news:fa415237.0402171619.552c2597@posting.google.c om... > What are the most common causes and remedies for engine backfire? > > (At least, I think backfire is the correct term for my problem... it > is an occasional loud 'bang' as if from gunfire, which seems to > emanate from near the catalytic converters under my floorboard rather > than up in the engine compartment.) > > Anyway, assuming that I am using the correct term... I have a jeep > with a fuel injected chevy engine, and it backfires from time to > time. Every occurence is when the engine is revving down (e.g., I put > the clutch in.) However, beyond that, there is no rhyme or reason... > sometimes it will happen 3 times in an hour, other times it might go > weeks with no backfire. I can't detect any other common factor > besides revving down (e.g., it happens regardless of whether the > engine is hot or cold, what gas I'm running, etc.) |
Re: Engine backfire
You may have a gap or hole in the pipe before the oxygen sensor. It will
eventually burn out your cat converter also and you'll have to replace it to make it through emmisions. Nick <ezeppelin@msn.com> wrote in message news:fa415237.0402171619.552c2597@posting.google.c om... > What are the most common causes and remedies for engine backfire? > > (At least, I think backfire is the correct term for my problem... it > is an occasional loud 'bang' as if from gunfire, which seems to > emanate from near the catalytic converters under my floorboard rather > than up in the engine compartment.) > > Anyway, assuming that I am using the correct term... I have a jeep > with a fuel injected chevy engine, and it backfires from time to > time. Every occurence is when the engine is revving down (e.g., I put > the clutch in.) However, beyond that, there is no rhyme or reason... > sometimes it will happen 3 times in an hour, other times it might go > weeks with no backfire. I can't detect any other common factor > besides revving down (e.g., it happens regardless of whether the > engine is hot or cold, what gas I'm running, etc.) |
Re: Engine backfire
You may have a gap or hole in the pipe before the oxygen sensor. It will
eventually burn out your cat converter also and you'll have to replace it to make it through emmisions. Nick <ezeppelin@msn.com> wrote in message news:fa415237.0402171619.552c2597@posting.google.c om... > What are the most common causes and remedies for engine backfire? > > (At least, I think backfire is the correct term for my problem... it > is an occasional loud 'bang' as if from gunfire, which seems to > emanate from near the catalytic converters under my floorboard rather > than up in the engine compartment.) > > Anyway, assuming that I am using the correct term... I have a jeep > with a fuel injected chevy engine, and it backfires from time to > time. Every occurence is when the engine is revving down (e.g., I put > the clutch in.) However, beyond that, there is no rhyme or reason... > sometimes it will happen 3 times in an hour, other times it might go > weeks with no backfire. I can't detect any other common factor > besides revving down (e.g., it happens regardless of whether the > engine is hot or cold, what gas I'm running, etc.) |
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