Calling ALL tech savies... 8.1L Probs

[496 BB]

This is beyond me at this point. Need to get this truck running and soon without hopefully spending all the coin for a new harness. Yes I know I should have went that route but it was a personal challenge and choice to do it myself. Heres my issues.

OK Im swapping an 8.1L in a 85 K20 and while I know the 8.1L is not an LS per se its close on what I need to know and PCM is the same (P59 LS1B controller). I do have EFI Live as well. Im not very proficient on it but know enough to get by sometimes.

Heres my problem. I have no spark on half cylinders (different from no pulse cylinders) and have no pulse while cranking on #2,4,1,3, and 7. I have signal from CKP and CMP while turning by hand and cranking read by a volt meter (10v). I have power and low ref to each as well. I also have power to all injectors. I tested pulse with a test light and pulse light (since they are 12v) and at signal wire on plug. I also tested everything including CMP and CKP and PCM pins. All are getting continuity between plug and PCM as well. PCM is NOT bad as I switched it and put in in my other truck which has same engine and it fired right up. So that is ruled out. I have good grounds in harness and not found a sensor that does not receive a ground or low ref. All PCM pins that are IGN are 12v while cranking as well. Same goes for grounds. I took all the split loom off and looked over wires and all seems to be ok from a naked eye standpoint. ALL fuses are good. Im using a CPW SA-1000 fuse block for engine. All wires were soldered and nothing half assed. Im also using the 04+ CMP sensor and timing set as they dont make the early style anymore and wanted to do it while engine was out of truck waiting to go in. Again that sensor gets a signal at PCM along with a low ref and 12v. So if it was not working I dont think there would be a signal. I aligned dots perfectly when I did it as well as far as I remember (would that cause no pulse anyways? Or just poor sequencing of injectors firing?). Engine never turned when I changed out old set to new set. Was done at TDC with dots lined up. CKP was a brand new updated sensor as well. Never messed with CKP reluctor. Could the CKP sensor give a good signal and still be bad? Im getting signal at pcm pins.

I did do this harness myself. I wanted to say I did it. Well thats biting me in the ass now. I know this engine is a rare bird but Ive had an 8.1L 2001 HD since I bought it in 2004 and love it. Great engines. I know this has to be something in the harness or sensor. I do know that when I was looking for PCM pinouts I had a super hard time finding one that matched up to the pins because the 01-02 were different in quite a few ways as the 03+. I tried Mitchell, MotoLogic, and All Data. All Data was what I settled on as it was the closet. I dont remember if any were off as I started this back in Feb. It was a spare time kinda thing and had help on wiring part by a very knowledgeable friend who knows these trucks better than I do.

So my question is has anyone had a situation like this before or no? If the PCM signal a ground to turn injectors on and half are working and half are not where does the pcm get those grounds from (Internally I suppose)? I cant seem to find any schematic that says where unless it gets a low ref from another circuit. Also why are some pulsing and others not? Seems like a pcm issue but its not. Do each injector have a separate ground from the pcm? I doubt that but dont know.

The truck has fired up for like 2 seconds before and stops. It loads with fuel obviously and shoots fireballs if I keep FP on which I dont normally. Im using my inline spark tester while cranking after I check something to make sure.

I just dont get it. I know its my fault but this will haunt me forever if I dont understand what it is. Maybe Im missing something as its obviously above my pay grade.

Thanks,
Chris

[4x4k30]

you need to check the grounds and make sure you have good grounds I had trouble starting my 6.0 I had a bad ground

[496 BB]

Ive checked all grounds at PCM and all are good. While cranking too. Finally got injectors to pulse tonight but still no spark. Reason for no pulse was cmp sensor bolt was apparently too tight and distorted it just enough to not read the reluctor wheel through all its sequence. Never seen nothing like it. Now Im still not getting a spark signal output from the PCM to the coils. Gotta be the CKP sensor but Im getting an output signal from that at the PCM so I dont know what gives. Lost.

[lowridergmc]

i have replaced alot of crank sensors on 8.1l for no starts.i have also seen where there is rust and corrosion build up under crank sensors pushing the sensor further away from the reluctor causing issues.

[496 BB]

OK so for anyone else experiencing this later on I FINALLY got it solved. Now it doesnt make one bit of sense but it works so whatever. It was the PCM bad. Now that same PCM I put into my 2001 HD with same motor and it fired the truck up just fine a week prior. Defies logic at best but my HD PCM works in the swap. I have no explanation at all.

Also would like the thank Howell, Hotrod Harness, and Fuel Injection Specialties for NOT responding to my emails 1.5 weeks ago regarding a harness or I would have already bought one and been out the $700 or so for something that would not have fixed it. Glad I trusted my gut on that anyways. Typical customer service though from over hyped companies.