I just started up a new LS1 conversion in a 94 formula firebird... Im using a Wait4MePerformance 99 conversion engine harness

It fired right up and i noticed a misfire in the car that seemed pretty apparent.

HPtuners shows no codes related to the misfire, only that it has a 100% misfire on cylinder 4, 8 and 5. It starts up no problem and idles with the mis, the miss doesnt go away when you bring the rpm's up.

I checked for fuel and has fuel on all cylinders. (checked with a noid, and swapped all injectors out).

Then I checked for spark and it has absolutely no spark coming out of 4,8,5 coils.

So its spark. I then verified it has all the grounds, even moved them to different bolt on head. Then I added extra ground wire from battery to frame and battery to engine. I then swapped the computer out with another fbody pcm with the tune loaded into it. I then swapped out the coil packs & the coil pack harness with another set. VATS is turned off fully...theres nothing in the tune that could be causing this.


Any ideas of what could cause 3 dead cylidners with no spark from the coils?

Im going to swap cam/crank sensors tomorrow and do a crank relearn. Im to the point im going to swap the wiring harness if i have to

 

It would seem that you're on the right track with the crank relearn, since it's strange to have no spark on 2 cylinders on one bank and one on the other.

 

I dont know what year the harness is from ( I believe its a 99). Im going to verify tomorrow. Only other thought is that its a 98 harness with a 99 computer. But I cant picture that even starting up would it?
The PCM is for sure a 99 (Ive tried two 99 computers).

 

I tried a 98 computer with vats turned off in the car today and it wouldnt start at all....

Also changed crank, cam sensor today..no change. Ordered a painless wiring harness, going to swap it in and see if it changes.

 

Did you try moving the coils to different sides and see if it follows? Maybe you have bad wiring on the coils or just bad coils?

 

Also do the pink wires on the coils all have 12volt when you have the engine running?

 

I swapped out the coilpacks with harnesses on both sides... no change

 

I'll check that today...thanks for the tip.

 

I fixed it.....finally after changing everything possible, I tried something i've never needed to use in 20+ ls1 swaps or 100's of tunes..

I did a case/crank learn on it and it completely fixed the problem. Runs great

 

did it set a dtc for that or did you have it disabled?