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P0300 confustion

Tiny
DUMENUF2TALK2U
  • MEMBER
  • 1998 PONTIAC SUNFIRE
  • 4 CYL
  • FWD
  • MANUAL
  • 110,000 MILES
I have a 03 pontiac sunfire, pulled an p0300 code (random misfire) and a bad cat code. I replaced the upstream O2 sensor and the cat code went away. I've replaced the plugs, did an oil change, compression reads around 170 on all cylinders, injectors work fine (noid light test and visual inspection of sprays), replaced coil pack, and wiped down the throttle body. It runs really rough, major power loss, and the cat is heating up to extreme temperature (I believe due to the excess fuel being sent to it). What do I need to test or replace next?
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Tuesday, February 15th, 2011 AT 10:29 PM

5 Replies

Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
What color are the plugs? Did you do an individual coil/cyl spark test?
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Tuesday, February 15th, 2011 AT 10:55 PM
Tiny
DUMENUF2TALK2U
  • MEMBER
  • 5 POSTS
The plug color? It was black, almost fouled but only on cylinder 1 and 4.

I'm not sure how to do a ind. Spark test on it as its one single coil pack
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Wednesday, February 16th, 2011 AT 3:59 AM
Tiny
DUMENUF2TALK2U
  • MEMBER
  • 5 POSTS
I'm not sure what you mean by the plug color? The #1 and 4 were foulded out if that was what you were asking.

I'm not sure how to do an ind. Spark test as its a single coil pack and there is only a spring that moves the current from the coil pack to the plug, held in place by pressure when you screw the coil pack down
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Wednesday, February 16th, 2011 AT 4:02 AM
Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
So you have/had 1&4 which has their own coil fouling out. Have you checked plugs since you changed them? Did you change ignition module? Do you have good spark on 1&4 now?
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Wednesday, February 16th, 2011 AT 7:26 AM
Tiny
DUMENUF2TALK2U
  • MEMBER
  • 5 POSTS
1&4 don't have their own coil pack, its one long strip that connects to all four cylinders. I did recheck the plugs and 1&4 had a heavy carbon build up. I cleaned them off and reinstalled. I did not change the ignition module as I assumed that if it went bad it would deliver no spark at all. I don't actually know that i'm getting good spark in any cylinder because I don't know if I can or how to do an ind spark test on a coil pack of that type
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Wednesday, February 16th, 2011 AT 5:49 PM

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