I have a complete (whole car, headlights to tailaights and everything in between) wiring harness and LS1/4L60E setup out of a low mileage WS6. I had some grand plan to use it all but now I'm scaling down. I am installing the engine/trans in an older truck (no smog) and now I have to decide whether to use the stock PCM or go to an aftermarket unit. Assuming that I will only be using the engine and trans with no O2 sensors or other body-related controls, is it better to mod the GM PCM or ???? Thanks...

 

Short answer: Even if you're putting the motor/trans in a dune buggy, the stock PCM will still work just fine.

In general, most body-related features such as ABS/traction control, interior lighting and keyless entry are regulated by their own control modules. The LS1 PCM is very flexible, so even if you are running the motor without a single emissions-related item you can simply tune the PCM and be on your way.

I saw that you mentioned you don't want to use O2 sensors. Are you trying to:
A) Use the motor with no catalytic convertors? In that case, you should probably keep the front O2 sensors active and just tune out the rears. The front O2 sensors are the only way for the PCM to adjust the air/fuel mixture accurately.
or
B) Trying to remove EFI completely and run a carb? In that case, no PCM is needed.

 

Since this engine is going into a 50+ year old truck there is no smog requirements to be met so I can run headers and dual exhaust...no need for O2 sensors unless they perform some function related to engine performance that I am unaware of. I like the EFI so the engine will remain in it's stock configuration...the original engine in this truck was a 292 POS so a stock LS1 is a quantum leap in performance and reliability. I am aware of vendors who configure harnesses to match applications, Speartech comes to mind, but since I have all the stock engine components and stock PCM I belive that all I will need is to disable everything that is not engine-related. Am I oversimplifying this?

 

Your front O2 sensors help the PCM figure out whether the engine is running rich or lean during part-throttle driving. Without them the PCM has no idea which direction it needs to tweak the air-fuel mixture. The engine will still run, but it will run in what's called open-loop... that is, it won't use any sensors. Gas mileage and performance will suffer.

Trust me, unless you're building a dedicated race car you want to keep your front O2s.

 

Good info, thanks!

 

You will be happiest with your truck project if you use ALL of the sensors that the engine comes with, except the rear O2 sensors if not running cats. You will need to have the PCM tuned for No post cat O2 sensors, No Theft--VATS, correct rear gear ratio, and tire size.