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Thread: obs ls swap electrical

  1. #1

    obs ls swap electrical

    New guy here. Been doing tons of research and have decided to swap a 6.0/4l80e combo into my 1997 gmc 1500 4x4. Its got the factory 350/4l60e right now. I've got some questions though.

    I plan to keep my original ecm to continue to run everything but the engine and trans. Keep gauges lights signals cruise etc. Running off old ecm. Then I want to use the donor trucks ecm for solely running the engine. I'm maybe a bit comfused as far as wiring goes. Is this what a stand alone harness is for?
    I will be taking everything from the donor including wiring harness, ecm, exhaust manifolds, tranny, and possibly torque convertor. Everything attatched to the engine basically.
    How should I go about this? By splicing the data wires the nbs ecm needs to run the engine from the old ecm? Or this is where say Nelsons stand alone harness comes in?

  2. #2
    I also think I'm going to find a 2002 as it should have the aluminum heads but still be dbc. Is there anything I need to do when converting to the 4l80e other than move my crossmember a bit?

    To make things simpler I'm following a write up on S&P's website where they swap an 03 (I believe) 6.0 into a 97 ukie. For ease of install I see myself using mostly S&P adapters etc. will See how it goes. I do have a few questions about the harness they have. Does it marry the old 97 harness to the nbs 6.0 harness?

    It seems to me if I used the adapters from s and p, where would the 6.0 ecm get its info (engine temp cam position oil press etc) from? I think I'm just confusing myself now.

  3. #3
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    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.
    Last edited by Mickeymotormount; 04-23-2013 at 04:00 PM.
    '93 Chevy 1500 4X4 ECLB with a '99 Silverado LQ4 6.0 and '99 Escalade 4L60E. SOLD IT!!

    New toy: 2001 2500 HD 4X4 Extended Cab Long Bed


    John

  4. #4
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    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
    98 GMC RCSB 2wd, 100% internally stock 305, w/twin T-3 junkyard turbos,Ramjet intake w/42lb inj,12200411 PCM. 4675lbs w/me in it. Best time in 5 passes 13.01@110

  5. #5
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    Edmonton, AB, Canada
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    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.
    Back Alley Motorsports 98 GMC
    -5.3l LM7 bored to 5.7l Thompson Motorsports -72mm T4 Magnum Turbo
    -TU1 Custom Grind cam(spec speed.inc) -799 heads
    -.660" Trick Flow dual valve springs -Forged Probe Pistons 3.902" flat top

  6. #6
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    Jeff, are you bypassing the anti-lock brakes or are you able to run them on the new harness and computer ?

  7. #7
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    Nothing gets bypassed.
    98 GMC RCSB 2wd, 100% internally stock 305, w/twin T-3 junkyard turbos,Ramjet intake w/42lb inj,12200411 PCM. 4675lbs w/me in it. Best time in 5 passes 13.01@110

  8. #8
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    Quote Originally Posted by Lextech View Post
    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.
    Last edited by kewljay223; 03-04-2016 at 11:12 PM.
    Like Tumbler in "Gone in 60" I'll drive anything with wheels or without

    My 95 ECSB LQ9 build thread - http://www.ls1truck.com/forums/lsx-t...to-95-obs.html
    CALI LEGAL ENGINE SWAP!
    Stock 03 LQ9, DBW, 95' 4l80e w/ Transgo shift kit, 2010 50# GM injectors, 2800 Circle D stall, Spectre CAI, Upgraded trans cooler, Home-made E-fans/shroud, Dual EP-381 fuel pumps w/Home-made hotwire kit
    NEXT ON LIST: Dual Battery setup, CAM/Valvetrain upgrade, Build my own rear mount turbo, TRU-TRAC, HIT THE STRIP!!!

  9. #9
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    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
    98 GMC RCSB 2wd, 100% internally stock 305, w/twin T-3 junkyard turbos,Ramjet intake w/42lb inj,12200411 PCM. 4675lbs w/me in it. Best time in 5 passes 13.01@110

  10. #10
    Join Date
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    Quote Originally Posted by Lextech View Post
    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
    Like Tumbler in "Gone in 60" I'll drive anything with wheels or without

    My 95 ECSB LQ9 build thread - http://www.ls1truck.com/forums/lsx-t...to-95-obs.html
    CALI LEGAL ENGINE SWAP!
    Stock 03 LQ9, DBW, 95' 4l80e w/ Transgo shift kit, 2010 50# GM injectors, 2800 Circle D stall, Spectre CAI, Upgraded trans cooler, Home-made E-fans/shroud, Dual EP-381 fuel pumps w/Home-made hotwire kit
    NEXT ON LIST: Dual Battery setup, CAM/Valvetrain upgrade, Build my own rear mount turbo, TRU-TRAC, HIT THE STRIP!!!

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