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Hi Eric,
I have a 2000 Chevy Suburban with 255K miles. A couple of months ago the engine started misfiring and the “check engine” light came on (the misfiring only lasted a few minutes). I had the code checked and it read misfiring on cylinder #2. Per the auto parts store’s advice, I switched the coil packs with cyl 2 & cyl 4. The issue didn’t re-occur so I dismissed it to a loose wire on the coil pack (I had recently replaced the water pump and assumed I must have loosened the coil pack wires at that time). A few days ago the engine started misfiring again and this time it showed misfiring on cylinder #8. Again, the misfiring only lasted a few minutes and the light turned off on its own in a couple of days. However, now the light came on and is reading the following:P0430: Catalyst efficiency low bank 2. Possible cause – catalytic converter defective, engine misfiring or engine condition, large vacuum leak
P0171: Fuel trim bank one condition
P0174: Fuel trim bank two conditionAgain, the code turned off on its own, but it has been misfiring on cold starts (no codes). Where should I start? Sorry for all the information but I felt the more I provide, the better
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I would address the lean condition first. check for
vacuum leaks and fuel pressure.This could be the misfire
your getting. The cat may have lost its ability to clean
the air.Put this on the back burner for now. Also check your
exhaust for any leaks before the cat. Pick and choose the symptoms
for some more help.http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
The o2 code is most likely a result of the misfire itself. When did this code appear? Was it when the engine was under heavy load on Highway? Does it miss at idle then smooth out when throttle is opened?
If the cel comes on under heavy load and disappears when throttle is closed or relaxed then I’d look at spark. If miss is at idle but smooths out when throttle is opened then I’d look at vacuum leak. With a vacuum leak the light tends to stay on. Does the cel flash then disapear? If so, it is fuel related and the cat can’t keep up due to lack of spark and raw fuel running through the exhaust into the cat.
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