obs ls swap electrical

[Mickeymotormount]

I may be able to answer some questions. Here goes;

You will need the new PCM to run the engine/trans combo. When getting the harness, get everything. It makes it easier when you have the complete harness. Even the harnesses going to the O2 sensors.
When it comes to using the old PCM, it's usage will be limited. Your guages will operate from the original senders mounted on the new engine. Your tachometer will get input from the new PCM as well as the speedometer. I believe the cruise also needs to be hooked into the new PCM. I think the only thing the old PCM will run would be the anti lock brakes.


As for running the 4L80E, you will need to move the crossmember back to accomodate the transmission's longer length. Since this is the case, the rear driveshaft will need to be shortened and the front lengthened as well.Unless, of course, you have the donor vehicle driveshafts and the wheel base of the donor is the same length as your truck.

S&P will be a big help with all the adapters and engine mounts they have. Stand alone harnesses usually need a source of keyed power, a ground and constant power. Not sure if they splice into your original harness with the exception of what's needed to run the engine.

Quite a few guys here have done this swap with this year truck. Hopefully, someone will chime in and correct/add to what I've said above. My swap was a little different as my truck is older and uses a '99 6.0 engine.

[Lextech]

You do not need to run two PCMs on a 96 and up truck if you are using a Gen3 engine with the LS1b PCM. The PCM with the 2-80 pin connectors. The LS1b PCM will run EVERYTHING on your truck just like it came from the factory.

Jeff

[shmiet]

For the oil pressure sender alot of people say you have to use the obs one with an adapter. I used the ls oil pressure sender as it was only one wire. My 5.3 was a 99 though.

[Ltz434]

Jeff, are you bypassing the anti-lock brakes or are you able to run them on the new harness and computer ?

[Lextech]

Nothing gets bypassed.

[kewljay223]

Nothing gets bypassed.

just to clarify, jeff, you stated a few comments ago that everything can be run off of the ls pcm if you have a 96+ truck. But if its earlier (88-95) as mine is the 95 (which is worse since its a transition year) what CAN'T be run??? i kept my pcm to run the ABS since mine wasnt the black pcm. other than abs, i use the new pcm for everything else. anything im missing?

EDIT: i also use stock DRAC box to control speedo but i later found out that i can use ls pcm to controll that too. that was my bad.

[Lextech]

kewljay,
I have never done an 88-95 truck. I have no experience with them. On the 96-2000 GMT400 body trucks it is a seamless upgrade. Every truck function that worked before the swap will work after the swap if it is wired and tuned properly.

Jeff

[kewljay223]

kewljay,
I have never done an 88-95 truck. I have no experience with them. On the 96-2000 GMT400 body trucks it is a seamless upgrade. Every truck function that worked before the swap will work after the swap if it is wired and tuned properly.

Jeff

ok. well im sure someone else might know. but thanks for the reply. Just gonna let my old one run the abs at this point. seems to be working fine. good luck

[Riddle88]

I'm doing a 5.3 swap in a 98 gmc sierra 4x4 using original trans whats easiest way to put the the two harnesses to gather