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Computer Comtrolled Related Question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Emmettology 101, Jun 12, 2000.

  1. Emmettology 101

    Emmettology 101 3/4 ton status

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    A friend of mine has an '89 GMC Heavy 1/2 to 4x4 p/u. Orignally it had a TBI350 with a 700R4 and now he is running a 383 ith an aftermarket TBI and a Rossler built 700R4.
    He is having problems with it and is debating wether or not to go to a carb. TPI is probably out of the question being that he doesn't want to spend a lot.
    Has anyone ever converted a newer vehicle like this to a carb and retained the stock tranny? The 700R4's are a lock up tranny, correct? And they are controolled asomewhat by the comp, correct?
    What can he do, if anything, to retain his train and get rid of the computer and run a carb?

    Thanks



    Mike
    1982 GMC Jimmy - Emmett
    http://emmett.coloradok5.com
     
  2. 89Jimmy

    89Jimmy 1/2 ton status

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    I can't help with carb swap info. I don't believe computer control of the tranny took place until the 4L80E. I'd sure hate to give up injection for a carb. (Just my humble opinion.)

    John

    So Much to do, So LITTLE cash.
     
  3. jarheadk5

    jarheadk5 1/2 ton status

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    Mike, I'm in southeastern PA (Phila. area) and I don't think that would be emissions-legal. I could be wrong though.

    Of course, if you know someone......who can do emissions......there really isn't much to worry about......

    [​IMG] Semper Maintenance!
     
  4. rick87K5

    rick87K5 Registered Member

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    Mike,
    I'd like to know what kind of problems he's having, because I'm conidering a similar set-up for my '87 K-5 (383 & TBI with a cam designed for maximum low to mid-range power). I don't want to spend a ton of $$ just to have similar problems. Thanks.

    Rick
     
  5. Emmettology 101

    Emmettology 101 3/4 ton status

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    The truck is having some missing problems. The guy who built the engine I wasn't too impressed with. He used a very large cam that didn't seem sutible for a TBI. A computer chip, I think, would have made it run better, but they never put one in. Also, They took out the knock sensor, I dont know if that was a good idea.

    Somehow he has an intermittent miss on a couple cylinders. They have changed wires, coils, Dist., and I think a few compnents in the Dist. and nothing sovled anything...

    He is just tired of playing with the comp system and figured it would be easier to just swap to a carb and be done with it.

    Mike
    1982 GMC Jimmy - Emmett
    http://emmett.coloradok5.com
     
  6. Emmettology 101

    Emmettology 101 3/4 ton status

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    Luckily we haven't had to deal with the crap of emmissions testing.

    Hopefully we wonthave to for a long time. They built a few testing buildings out this way about 4 years ago and somehow he idea was shot done and they used the buildings for other purposes.

    Mike
    1982 GMC Jimmy - Emmett
    http://emmett.coloradok5.com
     
  7. Emmettology 101

    Emmettology 101 3/4 ton status

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    I guess the only thing he needs to do is wire up the lock up on the tranny. It is supposedly controlled by the speedo, but his hasn't been working for a little while I guess.
    So he has two choices:
    1) get the speedo to work and run the lock up off of that somehow(the tranny locks up at a certain speed range.)
    2) wire it on a toggle switch and manually operate it.

    Mike
    1982 GMC Jimmy - Emmett
    http://emmett.coloradok5.com
     
  8. Mudzer

    Mudzer 1/2 ton status Author

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    Theres the problem right there. THere are several sensors that are required in order for the engine to run properly. The bigger cam not designed for the TBI does not provide enough vacuum for the MAP sensor therefore it is probably creating the miss. He also does not have a knock sensor which retards timing when detonation occurs, so he may have the computer retarding the timing some too. Tell him to buy a Crane CompuCam and install it plus install a knock sensor. THis would be less work and money than installing a carb. If he does not follow your advice, tell him to email me because I will take the TBI off his hands! I need spare parts anyway. Good luck.

    [​IMG]
    Mudzer 1978/91 K5
     
  9. HarryH3

    HarryH3 1 ton status Author

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    The computer should be setting the "Check Engine" light, which then makes it operate in "Limp Home" mode. It doesn't like the fact that it can't see the knock sensor input. The stock chip is also probably freaking out at the readings it is seeing from the MAP sensor. That rumpity cam changes the entire vacuum curve of the engine, which is the main input to the fuel delivery curve.

    He needs to put the knock sensor back. Then he'll need to get a custom chip burned that matches his engine and cam specs. The stocker assumes there's a stock 350 under the hood, not a radical 383. Once he sets it up right, it'll run like a bat outta hell!

    The computer only controls torque converter lockup on the 700R4. B&M sells a kit to make it work on non-computerized vehicles.

    <font color=black>HarryH3 - '75 K5</font color=black>
    http://ThunderTruck.ColoradoK5.com
     

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