360 Misfires

Probably a little early on this post but I thought I would ask the question to get pointed int he right direction. I just finished a compressor rebuild, belt service, and throw out bearing replacement on the 360. I had a CEL before I did it and I ignored it as the car came with a Tubi exhaust and I installed Fabspeed headers a few years ago as I thought one might have been cracked. The car runs great but would throw a CEL every so often usually due to the O2 sensor getting a funky reading because there are no OEM precats. I checked the code and I now have P0300, P0302, and P0305. These are for cylinder 2 and 5 which are different banks. When I clear it, it stays off for a little while and then comes on. Usually on start up. Thoughts on what to check first?

A couple notes:
1. The oil level is fine. I changed it and filled it correctly. It is in the middle when running and hot.
2. Cleared the code several several times. It comes back on the same cylinders and doesn't bounce around.
3. I plan to replace all of the plugs and reseat the coils tonight.
4. I am not sure that it would be a mass airflow sensor as it is on both banks.
5. Car doesn't stall of falter at idle or on a rev.

Any help will be appreciated.

 

Check for vacuum leaks around runners etc - maybe a smoke test too

 

I had something similar happen after a belt service. The problem was that the belt service was done poorly and the timing was off. At the same time if you have the original coils you might want to check those out.

 

You know he did the belt service himself, right?

 

I had misfire issues when I first got my 360 and replaced all the COP's. Misfire gone.

If you shop carefully, you can find the coils are a reasonable price. These units are subject to a lot of heat stress and vibration. They also operate at a high voltage and that can cause cracking in the insulation.

Changing them once every 20 years is a reasonable investment.

 

It isnt a problem on the belt replacement. I have 2 Testarossas also and I have done those 3 times. I have a 308 and I have previously done the 360 so I am confident in the fact that the belt service was done correctly

 

Last night I wapped the coil and cleaned the plug on cylinder 5 with cylinder 6. I cleared the code and restarted the car a few times. The code came back on cylinder 6 ans 5 was clear so I ordered new coils. I'm also going to replace the plugs. The Bosch coils are coming out of the UK so I will do an update after they arrive. By the way, as I mentioned, I had the CEL and a slightly rough idle before I did the belt service which makes me more confident that the belts were done correctly.