Hi all, looking for some help with my LQ9 swap into my K10. I have been trouble shooting for several days and I am out of ideas. Swap is essential complete. When I attempt start up, it will start up then shut off immediately, every time. I can get it to stay started by pushing on the accelerator pedal and can keep it started by feathering the pedal, however it back fires and does not run good. I sent the PCM to a reputable tuner to have VATS deleted and start up tune put on. I have HPTuners but wasn't confident enough to tune myself.

What I have done. My initial thinking it had to be VATS were not deleted. So I used HPTuners to confirm they were deleted. I used a BP Automotive Harness on the swap. I hooked the power wire to the truck's HEI wire(pink off bulkhead) and confirmed voltage in both cranking and run. Confirmed 12v at the coils during cranking and run. I verified fuel rail pressure with a gauge, 58 +/-2 psi. BP Harness has 2 grounds that I have checked, rechecked and rechecked again. Both are on driver side head. Checked injector pulsing with NOID light. Checked voltage and ground at injectors. I have checked and rechecked every connection. Tried starting with MAF and O2 sensors disconnected with no change. Verified rear O2 sensors disabled. I am getting what seems to be accurate RPMs on VCM scanner. Not getting any error codes on the PCM.

Info on the motor. I bought a 2003 Cadillac Escalade with 200k miles on it. Drove it home approx 60 miles. Ran really well. Then pulled the motor. 6.0 LQ9, DBW. Put a BTR stage 2 cam with new valve springs. Replaced most gaskets. New oil pump. Never pulled the heads. New Spark plugs and wires. Long tube Schoenfeld Headers. 2.5" full length, dual exhaust.

Any idea what to check next? What should I look for on VCM Scanner? This is my first ls swap and all seemed to be going well up to this point. Now I'm lost.

Any advise would be greatly appreciated!! Thanks in advance.

 

Stating that you can keep it running by feathering the pedal tells me that your issue is most likely throttle body related. Many times those DBW throttle bodies are junk or the sensors connected to them. Pull the intake tube off so you can see the throttle body as you try to start it and see what it does.

 

I don't know enough about HPTuners, but is there a setting in it for 24T vs 58T crank trigger? You mentioned backfiring which can be timing related.

 

Thanks for the suggestion. I pulled the intake tube, tried to start it same thing. Start and immediately die. I was able to watch the butterfly valve open and close as it should. Maybe I need to see if I can track one down and try a different tb. Unless there is another way to test it.

 

I really don’t know enough either. I would think being that it was the pcm that the motor came that it probably isn’t it. But I will investigate. Thanks for the suggestion.

 

Jam something in it to keep it open slightly and see how it acts. Its like the MAP, MAF and throttle body sensors are working against each other

 

Are you 1000% sure your passenger head has a good ground? Since you mentioned both harness grounds go to the drivers side head. All the grounds from heads to body/frame are present?

Are you able to get it to run enough that you can confirm all 8 cylinders are firing?

I would suggest to confirm the cam sensor wiring in the harness is correct. Its always possible its not right in an aftermarket harness, since there are 2 configurations, and sometimes they make an assumption on your setup, that is wrong, or they just re-pin it wrong.

 

86K10, I was wondering if you might have build thread somewhere? I am doing a LS swap in my '86 C10 with factory harness and interested in some things you might have done.

 

Thanks for the suggestions, I haven't been able to work on it for a couple weeks. Ill report back when I get back on it.

 

Sorry I didn't do a build thread. Happy to answer any questions you may have. Heres my email, I will be able to respond quicker to an email. rgibbs11@hotmail.com

 

I would check your coils to make sure they are on the assigned cylinder. It's easy to plug pass into drivers and vice versa. Then I'd check and make sure you have the injectors all where they are supposed to go.... it's easy to swap a few of those around as well. If those check out good I'd say it's tune related. Are you using stock injectors? Verify all injector data in your tune. I'd also throw a wideband on there to see what's going on with fueling. Did the tuner account for the cam swap? Box tunes are only as good as the person programming it with the information they've been given so make sure you gave him everything to make that initial tune. Good luck.

 

This has been a humbling experience. The number of hours I’ve spent trouble shooting this issue is crazy. I even went to the length of putting a different motor in the truck that I had sitting in the shop.
Well the issue turned out to be a ground. I have checked and repositioned all grounds no less than a dozen times. Made sure all grounds had clean metal contact, added more grounds all with no change. Checked ground continuity 100s of times with a multimeter.
Well as the issue continued I decided to check grounds 1 more time before I switched gears and put a SBC back in the truck. Well guess what…..I added a star washer to the ground from block to frame that wasn’t previously there and the damn thing fired right up and ran like a champ. WTF. How would a star washer make that ground better? It was definitely metal on metal contact before. My mind is blown that made a difference. Definitely an expensive and time consuming education.
The knowledge I have gained on these LS based engines in the process was worth it. (I guess). And now I have plenty of spare parts for the next one.
Thanks again for all the help.

 

You, Grasshopper, have found the secret to great grounds!

 

The star must have dug in to the metal for the proper ground. Sucks you went through all that trouble but at least it was something simple.