Misfre Help

86 Shelby Charger
Low mile 8v T2 engine out of 89 Masi TC
87 GLHS Stage 2 LM, 87 wiring
Currently no intercooler hooked up, wastegate hooked up to manifold, 5 psi boost max at WOT

Plugs are RN12YC Champions, new
Denso plug wires, new
Airtex/Wells cap/rotor, new
Stock OEM 31 year old coil

Under light throttle, there is no misfire at all. Under part/heavy throttle the car misses and breaks up badly. Sometimes it is worse than other times. Sometimes it will start accelerating well, then like flipping a switch, you can feel a loss of power and misfire. Or, it will start missing badly, then clear up and accelerate. Engine temperature seems to not change the symptoms.

Fuel pressure KOEO is about 50 psi. KOER about 53 psi at idle, 57 psi with vacuum line off regulator. Fuel pressure while driving remains steady, and under WOT up a hill will hit about 60 psi. This is using a snap on gauge ran up and out of the hood into the car.

I changed the plug gap from 35 thou to 25 thou and took it around my neighborhood. It seemed to help. The misfire seems to be more inconsistent, and before where it felt like multiple cylinders were cutting out, now it feels like only one cylinder is cutting in/out.

Any thoughts or tests I should perform before ordering a new coil?
Also, this setup was running GREAT for about 50 miles after I got it running. Then this started happening.

Wiggle the LM plugs and see if anything changes. Common to have bad terminals in there.

How's the cam timing? Spark timing? Try a different HEP?

also try wiggeling both ends of the coil wire

I had one that was lose at the coil and when I'd stomp on it the weight of the coil wire between the coil and the clip at the motor mount was enough to pull the contact apart just enough to cause a miss
it too was one ot those intermitent deals

No Vac/boost leak at the four way? If you used the Masi vac harness they tend to come apart there, I suppose they all do but the large 4mm vac line on the TC's seems to be loose on just about every car. Usually it sits symptom free until you start to up the boost.

Thanks for all the tips! Wiggled wires at LM, no change. Different HEP swapped in, no change. Replaced coil (Autozone had one in stock for cheap, figured it wouldn't hurt to have a backup if it didn't fix it) no change. I drove it to work today, 30 miles round trip. I didn't drive hard and stayed out of the boost. Sometimes it drives fine, sometimes it starts missing and falls on it's face. Anyway, I scoped out the secondary ignition, chocked the wheels, and made it misfire under load. Cylinder 3 waveform was indicative of a very lean condition. It is also throwing a code 51, but no power loss light. I'm thinking the 28 year old junkyard injectors have seen better days. More testing will be done. Also, I did find and repair a vacuum leak.

go over/rebuild the injector harness possibly too.

Brian

Injector harness is already re-built. Today it was barely running. Only cylinders 1 and 2 were firing. I have power to 3 and 4 injectors, but noid light doesn't flash. Continuity on injector ground to PM is good. Looking like the PM took a dump.

That is what it sounds like.

Alright. Much research done on how the injectors actually operate and the system/wiring. Wires traced and tested. Found a poor connection on the wire that fires injectors 3/4 going from the LM the PM. Loose connection was at the pm itself. I used a small pick to tighten the terminals up in the female connector. Drove to work today. Chirped the gears in 2nd. Ran really good. 15 miles/45 minutes in traffic. A couple of small hiccups but the tac was dropping too so I'm guessing a separate issue.