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Thread: 88 ls1 conversion

  1. #1
    Join Date
    Jan 2008
    BFE oklhoma

    88 ls1 conversion

    i am fixing to start my ls1 swap in my 88 obs, its 2wd, no tach, im putting a built 700r4 back in it with the rv cable conversion from bowtie and overdrives, the ecm is a standalone harness from speartech, all my question is making my gauges work properly.. do i keep the old ecm and let it slave off the new one or do i need to do some pinouts and delete it completely? and if so wich ones.. there is TONS of info and diargrams out there but most are for somone doing their own harness

  2. #2
    I know your question is kinda old but I did the same swap on the same model year SBSC. The wiring from the C100 connecter (Large Plug that does through firewall on drivers side) is where all your gauge wiring is located and this connector remains untouched during swap because it's all the basic stuff, lights, horn, signals, etc.

    The passenger side firewall is the computer wiring, a large bundle of wires about an inch diameter enters the cab and goes to ECm behind glove box. On these wires I hack sawed both sides and threw away everything except two power wires, one for HVAC fan and the other I dont remember but it was the only other red wire in the bundle.

    All gauges will be the same including speedo if you are using the same trans. For a tach I used the LS1 PCM tach out pin with a step up 12v ACC wired in to boost signal on my aftermarket tach.

    If you change gears or transmission then the speedo will have to be recalibrated. On 88-91 the cluster gets the raw AC signal from trans, yellow and purple wires, at a rate of 128,000 PPM and converts that signal to usable signals for ABS and cruise. Recalibrating a 88-91 cluster used to involve a special chip installed on back of cluster but they are long discontinued so a better way is to desolder internal cluster resistors and solder in a 7 position DIP SWITCH.

    Clear as mud? I hope this helped.

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