Misfire problem - Please help - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-24-2006, 12:15 AM   #1
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Default Misfire problem - Please help

Greetings:

I have a 97 SSE, and have been having the following problem.

I have been getting a check engine light off and on for a few months. It would come on and stay for a drive cycle or two and then go out. So I got a code reader and hooked it up to see what the error was. I got code P0302, which the book says is a misfire on cylinder 2.

Starting at the most logical place, I replaced the plugs. The old ones didn't look bad at all, but I replaced them anyway. Well, the next morning, I started off for my 30 minute drive to the office. Within the first 2-3 blocks of driving from home, I got 3 misfire error codes all P0302'*. I got one more about 10 minutes later and then none after that. For the rest of the day, about 5-8 drive cycles, one over 30 miles, I never got another error code. Sometimes, 2-3 hours would lapse between drive cycles, but still, no error codes.

The next morning, I changed plug wires. Started off to the office, and within the first mile or two, I had 3 error codes. Again misfires on cylinder 2. And then after that, I never had another one again that day. Same pattern of driving with 5-8 drive cycles, one of them the 30 mile trip back home, and still, no error codes.

The next morning, I changed the coil, for cylinders 2/5. I left for work, and again, I had the same, misfires on cylinder 2 for about the first 2-3miles, and then never again the rest of the day. For the next 3 days, I drive the car, and had the same result. On the first drive cycle of the day, 2-3 misfires within 3-5 minutes of starting, and then, none for the remainder of the day.

My question is....what else could it be? It is so strange that it is only the first drive cycle where I get the misfires. And then none the rest of the day. I am out of ideas. So I could use the collective wisdom of this group. I know that nothing damaging is happening, but I hate for that check engine light to keep coming on and going off because I don't want to get so used to it that I miss a real problem.

Thanks in advance for your suggestions.

Gary
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Old 07-24-2006, 12:56 AM   #2
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You could have swapped the plug, wire & coil from another cylinder. Try swapping a fuel injectors & see if the misfire moves. Check for vacuum leaks.
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Old 07-24-2006, 06:59 AM   #3
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Agree with Ted, additionally, try re-setting the PCM by disconnecting the battery for a few minutes. You will need the code to unlock the radio after power restore.
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Old 07-24-2006, 07:05 AM   #4
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or you could just pull the fuse for the pcm..... makes life so much easier
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Old 07-24-2006, 08:38 AM   #5
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I'm liking the fuel injector idea, even though 99% of these are plug or wire related. Check the #2 injector plug and harness for corrosion or damage. It'* the one closest to the alternator on the rear bank.
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