1996 Chevy Truck

I described the problem improperly. After testing for 1-4V AC on the module terminal B, no volts(.016) I tested for short to ground. The IC circuit was grounded at the VCM terminal 9, white wire. When I unplugged it the grounded circuit went away, and I determined the computer was the source of the ground. The computer has been replaced. Disregard the tach circuit and #8 terminal mentioned earlier.

The long story is that we installed a new long block. As old school mechanics, we missed swapping the crank reluctor so we pulled the timing cover off and installed. It ran but rough idle. We bought the OBDII scanner to set timing, not it, pulled intake for leaks, pulled cover again to check timing chain, checked lift to make sure it didn't have a bumpy cam, put it together- no spark. Found a ground off, but still no spark. Accidently left the key on so thought maybe some component damage. Distributer was new on install, bought crank sensor. Chk'd coil, module, no codes. Got talked into a VCM, no spark. Have run the flow chart over and over, changed meters, testers, there is only.016 V AC on module terminal B. The IC circuit is grounded, VCM terminal #8 white wire, but if you unplug it, it is open. The ground is coming from the computer. Any ideas?

I appreciate your responses, Docfixit. The schematic you provided is similar to what I have from Mitchell. The truck is a 1996 C20 w/ 7.4 VIN J. It died from a distributer drive gear failure. The long block came from an Ebay engine rebuilder. It had spark when we got done, but ran rough. We attributed the rough running on the first start-up to dist timing, but when curing that failed, we dug in and ended up without spark. Then we were thinking, what did we forget to hook up or what ground was left off or what wire is pinched, but we have exhausted ourselves on all of that. Now we have been chasing down the possibility of a component failure from leaving the ignition on overnight. I'm striking out. I am assuming a crank or cam sensor would produce a code. The crank sensor is new, the dist new on new motor install. I had a local part store test the module twice, they say it is good. Going through the No Spark test provided in another topic on this website (1996 Tahoe no spark) I went through the flowchart down to testing for 1-4 AC volts on the B terminal of the module. That's where I stall, as it does not have this voltage and the circuit is grounded. The grounded IC circuit doesn't exist unless it is plugged in to the VCM. Probing the VCM #9 terminal (IC circuit) with the C3 plug disconnected shows the computer is where the grounding comes from. I'll finish off with a nice donation if you stay with me on this.

After beating crank sensor on the floor, my spark returned. Replaced the new sensor, truck runs but set a p1345. Reinstalled dist. Many times, had timing at many locations, but can't get it down to 0 or 2 deg, 14 adv was the best, but can't do that again. It hangs out at 22 or 24, will adv a few with throttle, I have seen 31 once. Anybody?

As a supplement to the above question, I have followed the procedures described in manuals and Alldata. Com on dist installation. My aftermarket dist does not have an "8" marking as the target for rotor location on final placement, but I have had the rotor pointiing at #1 contact and the engine atTDC on compression stroke, and moved it 1 tooth each direction as well as rotated the dist housing to try to pick up 0 degree timing, with code cleared. It wouldn't drop down or even respond to changes. It isn't frozen on 24 degrees, as it will increase in timing with throttle application a few degrees. I've read some chatter about crank relearning, but there hasn't been any reference to it in instructions for dist replacement.

Yes, replaced Crank sensor. Old dist had bad bushing and drive gear, that's what took out the old motor. There won't be a white line to align to, as that would be if you were re-installing original dist. The new NAPA dist is similar enough, meaning that ultimately my target is to have the rotor pointing at the beginning of the flat part of the casting which is actually #1 cyl. I get that part, that's old school. I'm confident in the dist placement, my problem is that it still shows 22-24 deg adv on the scanner, and adjustment or even moving a tooth doesn't affect it. Two teeth makes it crossfire.