M54 Misfire Issue

[8920vt]

So I have a friend who's car we did a M54 swap on a long time ago. It uses all e46 m54 electronics and it has run great for probably 2 years now. Just two weeks ago it developed a misfire. We scanned it, cylinder 4 miss. Replaced coil pack, and plugs, continued driving. Misfire stayed constant cylinder 4. Swapped coils between cylinders, still cylinder 4 miss. No vacuum leaks etc. Now the other odd thing is, the miss is there some times and not at other times. We thought it may be temperature dependent but realized thats not the case. Continued to investigate and realized that if you cycle the ignition (turn the car off, and back on, the miss goes away). Now, if it begins to misfire, even driving down the road, we shut the car off and turn it back on, and the miss goes away.

Obviously we would like to find a real solution for this issue. Has anyone else encountered an issue like this?

I have not yet swapped injectors or other parts like that.


Thanks for any input.
ian

[328ijunkie]

All your doing when you key cycle is clearing the stored fault till it comes back. When ECU detects a 'cat damaging' misfire it will shut cyl off till the next key cycle.

[8920vt]

thank you very much, that helps me rule out other assumptions. ill try swapping injectors and a few other things and see if it jumps around. Thank you.