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Thread: hi starting a tbi conversion on 78 vette

  1. #1
    Carb and Points!
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    hi starting a tbi conversion on 78 vette

    just starting to piece together the harness and parts to start the conversion. please give me any advice you may have for this process.
    thanks
    reg

  2. #2
    Super Moderator dave w's Avatar
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    I think having a good wiring diagram is essential! I think either a Camaro or Caprice TBI systems from the early 90's are good systems to adapt for a Corvette. I like the fact that the Camaro and Caprice TBI system use a Manifold Air Temperature sensor.

    dave w

  3. #3
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    depending on what transmission is being run is what i would base my recommendation off of.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  4. #4
    Carb and Points!
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    The current engine is the stock 350, 4 bbl. It is a 4 speed transmission. I added vortec heads to it a few years ago. I found a 89 truck tbi setup, minus the ecm and vss locally for $100 that I am thinking about picking up. It is supposed to have all the the sensors, wiring harness, tbi and distributor. Does that sound like a good start?
    Last edited by cobrareg; 01-03-2013 at 08:43 AM.

  5. #5
    RIP EagleMark's Avatar
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    Yup, that will work for ya! ECM is about another $40. aftermarket VSS about $100. Lots of time and some tuning and you'll be stylin!

    EDIT: It's off a 5.7L engine right? You need the 5.7L TBI.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  6. #6
    Carb and Points!
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    With a manual trans, do I need to hook up the vss ? Some posts say I do and some say I don't. I was thinking about the in tank fuel pump. I've read that I can use the in tank fuel pump and sending unit from an 82 vette and it will work. Looks like the whole thing is about $170. Is this early wiring harness pretty easy to sort out, or will I need to buy one already tailored for the conversion? I can at least use a volt meter and trace wires.

  7. #7
    RIP EagleMark's Avatar
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    EFI Conversions are always better with VSS, that said you can go without on this ECM. That harness will be fine to rework. Nice deal you have an in tank drop in replacment, will need high pressure line from it to TBI then low pressure retrun line back to tank.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  8. #8
    Fuel Injected! gregs78cam's Avatar
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    If you haven't bought the harness yet, see if you can find one from a '94-'95 with PCM, there are many advantages to using the later PCMs. Or you can re-pin the early harness to work with the later PCM, either way it's not too hard.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  9. #9
    Carb and Points!
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    Most of what I have read says to use the early tbi ECM and wiring. What would be the benefit of using a later ECM and wiring harness?

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    Fuel Injected! JeepsAndGuns's Avatar
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    The only downside to the later tbi pcm's is a slightly steeper learing curve. While everything else is better.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  11. #11
    Fuel Injected! gregs78cam's Avatar
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    Quote Originally Posted by cobrareg View Post
    Most of what I have read says to use the early tbi ECM and wiring. What would be the benefit of using a later ECM and wiring harness?
    '7427 was basically the final OBD1 TBI PCM put out mostly in trucks/vans to cover most any engine/trans combination. Way more tables and constants to change, faster ALDL stream (~6 samples per second vs. 1 sample per 1.2 seconds) with much more to see, and a few extra things that users have figured out how to add for functionality(WBO2, E-Fan, MPFI).
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

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