PCM Connection issues?

[Zukikev]

I just put an LM7 into my 98 K2500. The swap is going fairly well, but I had a friend come over to delete the EGR, VATS, downstream o2 sensors etc. He said he couldn't see the pcm when he hooked up, but pushing the wires around a bit caused some relay clicking noises, and the fuel pump priming, and then he could read it. Now I have the engine running, but the connection is still very poor and it will die at random at times. The problem is definitely at the PCM. Usually what works best is pushing the wires down towards the ground, onto the pcm. See the photo for what I mean.

I will be building a mount to hold the PCM where it is in this location. I considered putting the Nelson fuse block into the factory fuse block, but it isn't a show truck so I don't think it is really necessary.

[bowtieguy79]

Didn't you post in another spot about your starter wire circuit? Where are you getting key switched power from? and is it secured properly?

[Zukikev]

Starting circuit is good now. I missed a ground. Doh! Starter turns without issue now with the key.

Its just that if the fuel pump doesn't prime, I have to move around the wires going into the pcm or have someone push and keep pressure on the big connectors going into it, and then with engine vibrations it sometimes loses that contact and dies. I'm 99% sure it is the big 2 connectors going into the PCM.

[bowtieguy79]

Starting circuit is good now. I missed a ground. Doh! Starter turns without issue now with the key.

Its just that if the fuel pump doesn't prime, I have to move around the wires going into the pcm or have someone push and keep pressure on the big connectors going into it, and then with engine vibrations it sometimes loses that contact and dies. I'm 99% sure it is the big 2 connectors going into the PCM.

Thats really odd. Your 100% sure the mounting bolts are tight? and you don't have any pins miss aligned? Did that once wouldn't let it fully engage.

[Zukikev]

All the pins are straight and the bolts are tight. I wish they had made those with a bolt on either side. My next step is contact cleaner and dielectric silicone, but everything looks like it shouldn't be causing me problems. As a last resort I could build a mount that clamps down the connectors. That sounds a lot like work!

Thanks for all your help bowtie!

[farmtruc]

Remove the connectors and and inspect the pcm terminals and connector terminals. Sometimes they get that white corrosion on them.
Use your buddies toothbrush and some cleaner to remove the gunk.
Spray it all off with electronic cleaner in a can.
Wouldn't hurt to put a little wd40 on the terminals either, just a light spray to keep them from getting...

[farmtruc]

If not, wiggle each pcm wire until you find it.
GM harnesses have been known to have opens.

[Zukikev]

Bump to this.

I had so many issues with this truck running intermittently in this install. It turned out to be grounds. I read somewhere online that the ls engines are picky for grounds and that the PCM MUST be grounded directly to the head. I ran a booster cable from the body of the PCM to the head and it fired right up and ran fine. Prior to that I had the PCM grounded to bracket that holds the ABS module, and then the other side of that bracket grounded to the engine. That was not good enough I guess.

Truck has been running fairly well for about 20,000km now!