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Discussion Starter #1
My question is why is my car back firing. I just replaced the FPR, O2 sensor, realigned the throttle switch because I had erractic idling. My MAF is 4 years old by NAPA, replaced the TPS 6 months ago. Cat Convertor is 1 year old. Replaced the intake manifold gasket and valve covers. Ran ECU codes and nothing. Wires are fine and the timing is good. Cleaned the K&N FIPR and replace all the engine vacuum hoses.

What the car does is it does this off and on though. Like at times I would drive my car and park it then come back for about 20mins. Start the car up and then it stumbles a little and then I put the car in DRIVE to drive away and then thats when the back fire gets bad when I hit the accelerator. It is more noticable when you hit the accelator pedal. I think the factor might be a Air Temperature or breathing.

Can you guys help me out here?


DenZeL KnighT
'86 300zx non-turbo w/auto w/digital dash

If you wanna ride...ride in stttylllee!!!
 

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I know that a broken valve spring can cause alot of backfiring, other than that it may be ignition related. When a spring breaks say your exhaust valve spring and when theres a combustion in the cylinder the exhuast valve does not open so the cylinder that just fired will shoot the air back up through the intake valve and out of the intake.
 

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Recheck your distributor cap (tighten if it is loose), check the gap on you spark plugs and also recheck the vacuum lines.
 

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Discussion Starter #4
I already did the distributor cap thing and also i put the spark plugs in about fall of last year. Would the gap change between that time?
 

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verify your ignition timing with a timing light. if the timing is off it can cause backfiring.
If that isn't it, I would actually open up the timing belt cover and crank it till its at TDC of compression stroke and verify that the timing marks are lined up. Your cam timing may be off slightly allowing the combustion to exit when the exhaust valve opens.
 
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