496 BB

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 #2,4,3, and 7. I have signal from CKP and CMP while turning by hand and cranking. I have power and low ref to each as well. I also have power to all injectors. I tested pulse with a test 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. Engine never turned when I changed out old set to new set. CKP was a brand new updated sensor as well. Never messed with CKP reluctor.

I did do this harness myself. I wanted to say I did it. Well thats biting me in the *** 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. 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? I cant seem to find any schematic that says where unless it gets a low ref from another circuit.

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. Im already going to buy a stand alone harness from someone reputable at this point but thought Id ask you guys first. Maybe Im missing something. Obviously above my pay grade.

Thanks,
Chris

RixTrix

Power?

Injectors are grounded by the computer. Usually power is daisy chained through the harness to each injector.

Or you have a batch fired computer and only 2 channels and 1 is toast.

ledesordre

iTrader: (9)

Grounds are eyelets that attach to the back of the drivers side block. There should be 2-3 of them.

I'd also check the fuse box, injector 2 and injector 1 fuses. look for 12v there on both with key on.

496 BB

I have always had 12v to hot side of injectors. Those grounds (1 eyelet with 2 wires and a single eyelet) I have hooked directly to battery negative now that is also grounded to block and frame. Im pretty sure these are batch fire ONLY at startup and sequential like LS when running but what stumps me is its firing at least 2 injectors from each bank. Would the channels be each bank or mix up banks? I have injectors wired by bank. Left bank is fuse and right bank is a fuse. BOTH are good.

So based off the LS1B PCM where does the PCM get the ground for firing the injectors? Is it just those grounds on back right cylinder or does it get it from another low ref from another pin? If I find that out I can double check. I guess I could trace the ground from main harness but that would only prove what I already know....its good. Need to know where PCM gets the ground supply for each injector inside the pcm.

Does efi live scope ckp and cmp? I cant find anything about it. Need to see if they are talking correctly.

496 BB

OK so got the injectors pulsing tonight. Long story short it was the bolt on the cmp was too tight and distorted the stupid sensor just enough to apparently not read it correctly. Anyways they seem ok now.

Still not getting spark. Getting a signal at the pcm from the ckp (10v turning crank by hand) but nothing out of the pcm for coil signals. Weird. Thoughts?