Hey.

I lost a spark plug while driving my '03 OEM motor several months ago. My "mechanic" was able to Heli-Coil the head, replace one coil pack and the one plug. The engine now runs but it idles/runs rough and the engine service light is on 100% of the time. The codes indicate multiple cylinder mis-fires. Could there have been additional internal damage that would cause mis-fire codes to be thrown? Seems like an electrical problem but I've already swapped out both coils a 2nd time.

Anyone have some recommendations they can throw my way?

 

Did you get that code prior to the engine work? Evo 8s had those random cylinder misfire issues, and your tuner could check it out for you.

 

Could it be the spark plug is not grounding correctly because of the helicoil?

 

is it possible the other coil packs were shorted? i'd start with checking all the plugs, if you had issues with one plug, it's possible to have issues with other plugs.

 

 

Thanks for all the suggestions so far.

The misfire codes have only been a problem since I had the car fixed after the catastrophic event happen a few months ago. Both of the coils that I replaced a couple weeks back were bought used but were supposedly in good operational condition. I haven't tried changing all the spark plugs - I'm going to do that today.

As far as the Heli-coil repair, how would I correct for a grounding problem? I do have a DVM and I'll check the continuity between the threads and ground on each of them when I have the plugs out.

Is there anything else electrical that could cause the misfire? The actual event was pretty severe - I was on the freeway under boost and heard a huge boom immediately followed by no power and lots of noise. I had to drive the car almost 8 miles back to my mechanic. In hindsight, this probably wasn't wise but I think the damage was already done. The plug blew out one of two coil packs, so the car was only running on 2 cylinders.

 

What cylinders are misfiring in comparison to what coilpacks were replaced? Might be your problem right there if you went used on them...I just don't trust used electrical parts like coilpacks.

 

The current misfire corresponds to the cylinder that was repaired. However, I have recently seen codes that indicate random cylinder misfire. (I've cleared the ECU a few different times wishfully thinking the problem would solve itself.)
I just changed out the remaining three spark plugs and gave it a 10 min test drive. Seems to idle about the same and I didn't read any new codes; it usually takes 75 miles or so to show up after clearing the ECU.

The other thing I noted was a small hole in the intake manifold between cylinders 3 and 4. I don't hear any leakage so I'm assuming it's just an artifact of the way the casting was poured.

I also have a short video that I took so you guys can listen for misfire. (This is a bone-stock motor with just a manual boot controller and ECU reflash). Here's the link:
Fingers crossed the plug replacement has resolved my problem...

 

It's hard to tell from the video, but it doesn't sound too bad to me. I hope those plugs take care of your problem. As for that hole in the intake, I doubt it's actually anything to worry about. Maybe you should spray some carb cleaner in the area while the engine is running, if the rpm rises, then you know there is a vacuum leak.

 

If you're getting a misfire in cylinder four, swap the coils around and see if the misfire follows the ignition coil. If it is you should get a p0302 code.