I've been having issues with my gen 4 swapped ST165. The engine is pretty much stock besides a set of stock compression Wiesco pistons, rods and head studs. My harness was done by WireGap. For the longest time, I've had a wierd misfire/ignition breakup issue under load. Sometimes it was violent, like a boost-cut. I've done quite a bit to try to solve the issue. New plugs, coils, grounding, I re-pinned the connectors to the ECU, and many other things. Recently, I pulled the engine harness out to clean it up. Checked crimps and soldered connections to make sure all is well. I found some potential problem areas and addressed them. I put the harness back in and drove...the ignition still broke up and cut out. I was a bit pissed...Then on a whim, I decided to pull the ground off of my MSD Tach adapter and the car runs perfect!!! Pulls to redline at 16lbs of boost with great AFRs. I figured the tach adapter is the only thing in the ignition/timing system I have not messed with. I guess it was causing issues with the ECU.
Has anyone else seen weird issues like this? Does anyone know of a different solution to get my stock tach working?