Okay, here goes. I'm building a 79 Stepside with an LY6 from an 08 Sierra and a 6L80 from a Pontiac G8. I'm finally trying to start her up, and all it does is crank all day long. I've checked every ground, every power wire, tried using every single wire in the ignition switch harness as my "Hot in ON and START" wire (I'm using a PSI Conversion harness), but no matter what, I get no spark. I've checked voltage at the coils, and all is well. I have fuel, and my PCM was just reformatted with a new tune to rule out any tuning issues. I don't see any recessed pins in the PCM connectors, and I don't see any obvious broken wires anywhere. I've checked voltage and resistance pretty much everywhere. I replaced the Crank Position Sensor because I wasn't getting RPM, and now I am. I haven't replaced the Cam Position Sensor, but it should start up regardless of that.
My wiring, as of right now (using
this diagram):
Grounds:
Engine to chassis
Battery to chassis
Engine to body
Two PSI harness grounds to the back of the driver's side head
Positive:
Battery positive to starter battery positive post
Starter positive post has connections to Pin 2J on the firewall
Starter positive to junction block
Starter positive to two battery positive terminals from the PSI harness
Junction Block goes to alternator and Pin 2E on the firewall
Starter S post goes to Pin 6 on the firewall
The "hot during ON/START" has been tried on the cab side of Pins 3 and 25 (as well as almost every other one in the ignition harness)
I can't figure out what I'm missing. I had to re-run brand new wire and Type 56 terminals to the firewall because the original harness in this truck was completely trashed.
The weirdest part is, earlier this week, the truck started up for a couple of seconds, 5 or so times in a row. I had it connected to a laptop and an EFILive autocal so I could log whether or not it was even commanding spark, but it fired up instead. I've tried the same thing multiple times since, and I can't get anything from it.
Any help or direction you guys can give me would be appreciated. This is the first time I've ever built a vehicle, and until now it was going great.