Hello, guys.
I'm working with a 4.8 swapped '89 Firebird. Stock LR4 longblock, factory tune, approximately 180-200 psi cranking compression.

Only codes are a P0300 multiple misfire code, and a P0101 MAF code that shows up shortly after clearing (but MAF sensor is giving a signal).

I"m getting an intermittent misfire on bank 2 (2-4-6-8). The problem usually begins shortly after startup, and usually doesn't last too long. It might do it randomly while driving for a 5-10 seconds, and then snap out of it.

Because it's an intermittent problem that usually goes away after a few seconds, I haven't really made any progress with troubleshooting, but this evening, it started ******* up in the driveway, and I got some results (but no answers).

These are the following checks that I've done:

-fuel pressure is a constant 58 psi.
-voltage at injectors and coils is 13.9V
-injectors are pulsing.
-Coils have spark.
-Changed the coil harness on that side for a good used one.
-All the ground wires on the harness are connected, and I've got them connected at three different points on the cylinder heads. For that reason, I don't think it's a grounding issue.

I hooked up a scanner, and you can see how the misfiring is mostly contained on the even bank:




Something else I noticed was that the fuel trims on Bank 2 were out by a mile when the misfiring occurred. They returned to normal when it stopped, matching bank 1.




I'd really appreciate any help you guys could give me, and I'll answer any questions y'all have.

 

Check for a small vacuum leak on the #2 bank intake area