PCM wiring for LS Swap

Covetd

Covetd

New Member
Original poster
Joined
Nov 15, 2021
Messages
3
Location
Midwest
Hello! I'm in the process of an LS swap. I started with the stock 4.0L 42RE auto and have installed a 2005 5.3L / 4l60E using many parts from Novak Industries for the swap. I intend to keep the Jeep wiring harness to retain factory gauges/controls along with the re-worked (by Novak) GM harness to run the LS. I pulled the Jeep harness out and removed from it the following circuits to clean it up:

1) O2 sensors
2) Coils
3) Injectors
4) Transmission controls

I have the new motor / tranny (adapted to the original np241 t-case) installed now and I have both the Jeep and GM harness re-installed and connected. I have the battery grounded to the frame, frame to engine, engine to body at original firewall location as well as the firewall to hood factory grounds and have validated continuity between them all. There is also a small ground coming from the cabin through the firewall at the passenger side under the battery tray I have grounded to the frame.

Problem is though, when I connected the battery and turned on the ignition, I have NO POWER inside the Jeep. Everything worked properly before I removed the engine/harness. I am leaning towards a missing ground to the PCM, but I'm not sure how/where the PCM is grounded / powered?

Anyone who might be able to help nudge me in the right direction to troubleshoot this?

Thanks!
-Todd
 
I know on the 4.0 Jeep harness there is a bunch of ground wires on the right side of the engine block where the factory ground cable attaches.
 
NskLJ said:
I know on the 4.0 Jeep harness there is a bunch of ground wires on the right side of the engine block where the factory ground cable attaches.
Click to expand...
Thank you for the quick reply!

That's the G105 ground...I grounded those wires to the ground at the firewall since that's where the wires are closes to. Do they HAVE to be grounded to the block for some reason?
 
Cool - thank you again!

Good news - One of the plugs at the drivers side kick panel was not fully seated, now I've got power everywhere that I expect it and the engine is cranking as it should. I'm going to prime it and check oil pressure, then test fire and see if this was all for naught 🤞
 
  • Like
Reactions: ColoJeep
Covetd said:
Cool - thank you again!

Good news - One of the plugs at the drivers side kick panel was not fully seated, now I've got power everywhere that I expect it and the engine is cranking as it should. I'm going to prime it and check oil pressure, then test fire and see if this was all for naught 🤞
Click to expand...
Awesome, glad to hear.
 
Top Bottom
Back