Quote:
Originally posted by green94droptop:
I have that same noise at start up when car has been sitting for a while.
Been told that it has something to do with the smog pump warming up the car.
But mine didn't start to do it 'till I put in my o/r h-pipe.
Don't thing it causes any harm though.
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You're running lean, not rich. It's probably caused by your off road h-pipe. Use the search engine to find Rebel79's off road h-pipe fix. Your O2 sensor's don't work when your car is cold, you run in open loop, but my guess is your computer is taking closed loop info and adjusting your open loop cycle.
Your smog pump has nothing to do with it.
Light backfiring when cold also signals clogged or poor working fuel injectors. Have your injectors cleaned.
I wouldn't expect the oil change to do a whole lot, unless you had a sticky lifter from bad oil, if you are backfiring through the intake, and an oil change fixed the problem, I'd be suspect of a sticking valve.