Nor is the ECU talking to the scan tool.

That's probably where I'd start. You have correct power and grounds at the OBD plug? Correct wire from pcm to OBD plug? If PCM power or grounds are not right it obviously won't communicate either so it sounds to me like you may have missed a wire somewhere. Go back through and check all power and ground inputs to your PCM, sucks but I'll bet you'll find the problem. Good luck

 

I do have power and serial data at the obdII plug but i didnt check the grounds there...Im going to go back over everything one by one again... I also forgot to mention this motor is a upullit item that was in a suburban that got T-boned pretty bad if that matters. Thanks for the input

 

I do have power and serial data at the obdII plug but i didnt check the grounds

Just re-read this, how do you know you had serial data if you couldn't talk to it. Checking your grounds would have taken two seconds. By any chance did the scan tool you were using "wake up" or light a led showing power at the dlc ??

 

Check the wires you might have missed something. Make sre everthing is gounded goood as well.

 

So I know you got power to the Computer but are you getting ignition power to everything? X2 on missing something.

 

How many external grounds does the stock harness have? i have only 2 grounds with eyelets on them, one thats black and white and one with 2 blacks crimped to one eyelet that come out behind the motor.

 

Depending on how much you've cut out of the harness of course, but I think there are 3 or 4 ground eyelets on the back of the motor. Have you unplugged the PCM, grabbed your connector diagram, and made sure all your powers (IGN and B+) and grounds are there?

 

Make sure your motor is grounded to the chassis and/or the battery as well.

 

I just unplugged the ecu and double checked all of my power and ground leads, all are functioning properly. This leads me to believe that the ecu was flashed incorrectly or there is a back feed from something that is freaking out my ECU. This is very weird to me, The DBW works just fine but there is still no communication with the scan tool or spark...

 

no communication with the scan tool

I'd be chasing that......

 

Neutral safety switch? Dunno, just a idea.

 

Jeff at MFS is pretty sharp on the wiring stuff. I bet he could sort it our for a reasonable sum.

my guess is that it is in something you removed from the OE harness

 

just saw that you have been dealing with PF. give them a call. they know their biz and will have answers :smokin:

 

Thanks for the advise guys. I did find one ground that wasn't hooked up:homer:, but once it was hooked up it didnt change anything. Still no communication with the scanner and no spark. The Throttle body is still functioning though:flipoff2:. Im just going to have to get a harness from pacific fab and go from there.


EDIT: harness should be here monday!

 

Can you get a stock ecm to check with. I know it will throw codes but it should start the motor.

 

another suggestion on ensuring proper grounding. I had gremlins in my setup and that was the primary feedback, and another statement to ensure the motor is grounded to the frame or the battery in case you haven't done so.

I have also heard of issues where the ground inside the computer has caused problems. I'm still not sure I've figured out what my problem is with my 4.8L but I'm going to get another computer flashed just in case. just to let you know, my issue made it so I wasn't getting spark AND my fuel pump wasn't turning on.

Is it possible that a faulty MAF will cause this problem? I had a previous GM mechanic tell me when the trucks would come in not running or having intermittent running problems, they'd start the rig up(or turn it over) and then give the computer and then the MAF a good rap with a wrench to see if something inside was loose.

good luck. great engines but a bitch when they have electrical issues.

 

Thanks again for the suggestions. I do have a large 4g wire running from the block to the frame then to the battery, the body is also grounded. I took the wiring harness completely out and checked everything and now im just buried deeper in questions :flipoff2:. I ended up just ordering the new harness from Pacific Fabrication. It should be here monday. This will tell me if my harness was the problem or if the computer needs to be reflashed.

 

Tyler. We are pleased you got it up and running. Hope you enjoy the swap half as much as we do.