Mercruiser+Jeep+TBI

Discussion in 'Injection Tech' started by Otto_, Dec 1, 2017.


  1. Otto_

    Otto_ Farmall Cub

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    I was directed here from the CJ2a page via a thread that a member had started about working with Bill on a kit for his vintage jeep. He seems quite happy with it and I’ve always been curious about adding a simple TBI system to my jeep. My jeep runs a Mercruiser 4 cyl (Chevrolet) that has a one bbl Monojet carb that I’m not happy with. My goal with the TBI is primarily solving some drivability issues, but if better fuel economy or power are a byproduct- all the better.

    I’ve read through a lot of the information here and I think I’m at the point of chasing parts but wanted to confirm that I’m going after the right ones- don’t want to buy twice! My jeep’s engine is a 3.0L so the 2.8L TB seems like the logical choice even if it’s for a slightly smaller engine, it seems sized closer to my 3.0L than the 4.3L. My thought is the smaller TB might offer better throttle response (which is what I’m after).

    On my last JY outing, I spied a 1991 S-10 with a 2.5L 4 cyl that had a complete wiring harness, computer and all the sensors but it looked like it would only support one injector. Will any GM wiring harness work or does everything have to match? Can parts be mixed? i.e., TB from one vehicle, harness from another, and the 7747 ECM from something else? Most of the donor vehicles are coming up on 30 years old, not exactly hanging from every tree.
     
  2. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    Is this the carb you have? Standard 2 bolt mounting flange?
    [​IMG]

    If so then you have a choice of running the 1bbl or 2bbl throttle body.
    I have developed adapters for both applications that you may have seen in the adapter FAQ thread.
    This is late model 1bbl that was used on cars and trucks. Much smaller and nicer then the early 1bbl that was used on the 2.5 and corvette crossfire system.
    HFI-1.jpg DSC03143 (640x480).jpg

    This one will allow the 2.8, 4.3, 5.0 and 5.7 TBI to bolt on to the 1bbl manifold.
    The 2.8 throttle bores are 1 3/8 and the 4.3-5.7 are 1 11/16.
    Physical size is the same.

    DSC03144 (640x480).jpg DSC03147 (640x473).jpg

    Either one will work.
    For the Harness, I always start with a 4.3 or V8 harness. The 2.5 had some things that were different and used a different ECM making conversion longer and harder then needed.
    The harness from a full size van is the longest and since you end up cutting and splicing every wire, I normally try to start with them. But the standard pickup harness will work fine especially in your small application.
    If you don't want to spend a week on your garage floor tailoring the harness I do have all brand new standalone harnesses. They have built in fuse block and power relays.
    Just plug and play.
    HFI System-med.jpg

    You can also see a complete list of the parts and services i offer by clicking the link that takes you to the machine shop forum.
     
  3. Otto_

    Otto_ Farmall Cub

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    Thanks for the prompt response Bill, I had planned on using one of your adapters. And yes, that is what my carb looks like. BTW I also own a Scout! Please feel free to display it in readers rides.
    rf.jpg
     
    walkersscout and scout2000 like this.
  4. Otto_

    Otto_ Farmall Cub

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    I scored a 2.8L TB from an ‘88 s -15 at the JY today. I also found an ‘88 Suburban that had an intact wiring harness, is this a good candidate? It seemed to be the simplest vehicle to remove the harness from. It was 350 powered with an automatic but had the 8674 ECU.
     
  5. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    Get the 4 letter code from the ECM. That number doesn't match the normal service number.
    Should be a 1227747
     
  6. Otto_

    Otto_ Farmall Cub

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    I finally got the system on the jeep and it actually runs! I have some questions though:
    The timing is set to 0 with the coupler disconnected but it reads 15 btdc at idle with it connected. Sound right?
    Also having difficulty getting the engine to idle under 800 rpm even after going through the procedure many times. IAC reads between 20 and 35 or so. Any ideas? TPS reads a solid .61V. I’m still tickled that it actually works.
     
  7. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    What chip and ECM are you running?
     
  8. Otto_

    Otto_ Farmall Cub

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    It’s the 7747 ECM and the chip is from Hamilton Injection. Just want to get the basics right before logging possibly worthless data.
     
  9. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    Any error codes? SES light.
    Is the fuel pressure 11-13psi and no changes?
    What's the last name?
     

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