1999 Pontiac Grand Prix What are causes for random misfires

Tiny
BANDITGTP
  • MEMBER
  • 1999 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 162,000 MILES
I have been having this problem for quite some time and I can't seem to nail the cause down. I have a lack of power and I can get my CHECK ENGINE light to come on every day if I want to. Every once in a while it would be for a specific cylinder but 95% of the time, I get the code for random misfire. So far I have changed:
Spark Plugs (twice)
Wires
Ignition Coils (all 3)
Ignition Module
MAP Sensor
Air Filter (twice)
Fuel Filter (twice)
Fuel Pressure Regulator

I have also checked and verified the fuel pressure is correct.

Are there any other sensors that may cause this code and engine performance?

Any help would be greatly appreciated.
Thanks
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Thursday, January 28th, 2010 AT 8:49 PM

3 Replies

Tiny
BMRFIXIT
  • EXPERT
My next step would be a compression test and then checking the injectors
try and have the fuel injectors clean
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Thursday, January 28th, 2010 AT 9:05 PM
Tiny
BANDITGTP
  • MEMBER
Would dirty or clogged fuel injectors cause misfires? Do you know what some other symptoms would be for bad injectors. Would a fuel injector service at a local repair shop clean them if they were clogged or would they need to be replaced?
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Wednesday, March 10th, 2010 AT 8:10 PM
Tiny
BMRFIXIT
  • EXPERT
Should have the injector cleaned for sure
but the service should be to isolate and clean the injectors and not just add some cleaner to the tank, as you can do that your self
special top cylinder and fuel injector cleaner should be used
as recommended by the factory

also check this if it apply to you
STB

General Motors Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter. These alarm systems use a circuit interrupt which utilizes the ignition circuit on the vehicles.
These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Over time, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly.
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Thursday, March 11th, 2010 AT 6:18 AM

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