99 GT Multiple misfires - SES light flashing non stop

[isra2003]

Hello all. . haven't posted anything for a bit but I have always dropped in to soak some of your knowledge. Unfortunately having issues with my GP 99. I was driving home last night and it just started shaking and the SES light flashing non stop. Also there was this foul burning smell coming inside the car. Had it scanned and received code P0300 multiple misfires which is what I already knew. I figured it was the plugs since I have not changed them since 80k, my car now has over 172k. So I changed plugs and wires today and it still doing it. So since that code can be caused by multiple things I don't want to go ahead and start replacing things. Any suggestions on how to narrow it down. For what I've read around in the forum and other sites I'm leaning towards a faulty ICM. How can I test it? Any suggestions/help is highly appreciated.

[GTP Dad]

If the wires and plugs didn't change things then look at the coils next. Usually random misfires are not coil related due to the fact that you have three coils and they usually don't all go at once. The ICM could be have gone bad as you indicated. Unfortunately I can't give you a good way to test it at this point.

Also, it is possible that you have a fuel starvation problem. When did you change the fuel filter last? If it is original then it may be blocked. You could also have clogged injectors. This usually doesn't show up in the fashion you discussed but anything is possible.

You can check the fuel pressure with a fuel pressure gauge and they can be rented. Make sure to check it with the car running so that you will see what type of pressure you are getting when revving the engine. If it drops too low then the fuel system is the culprit and a blocked fuel filter can cause this.

[isra2003]

Thanks GTP Dad for your reply. And yes I inspected fuel pressure, its good. Had a friend who's a mechanic do some diagnostics while I'm at work and called me to say its a bad ICM. So I will probably replace it today after I get off. I'll keep you all posted.

[isra2003]

Fixed!!! ICM was bad. . This thing is a beast. 172k miles and still running strong!!!

[Tech II]

That was a good guess......could have easily been a coil....that's why you test/diagnose first....