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I wish I had a clue! TBI swap stuff...

Discussion in 'The Garage' started by divorced, Mar 11, 2005.

  1. divorced

    divorced 3/4 ton status

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    Almost useless rambling and a few questions:

    Ok, I pulled the motor from my 1989 C1500 to put in my 1979 K20 and there are way more wires than I thought! There are two groups of wires that come through the firewall: one on the passenger side and one on the driver side, and they both connect behind the engine near the distributor. I guess I need to take them apart and see what wires do what? Do I still use the current starter circuit for the K20? And the K20 alternator wires? The wiring harness on the passenger side came through the firewall and went to the computer and also had two other connectors that went under the dash. It looked like one went to the driver side and the other to the heater/AC fan, they are circled in red and yellow in the pic, what are they? Do I need to take out the diagnostic port thing from the donor truck? What do I use for a check engine light? If you're still reading, sorry for so many questions. I am really lost on this and don't want to screw it up.

    [​IMG]
     
  2. slyguy_22

    slyguy_22 1/2 ton status GMOTM Winner

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    I'll have to double check but i just got done putting my 89 k10 front clip motor & trans in my 79 K5. as for the check engine, i would go to the junk yard and find the gauge set from a 88-91 k5 your whole wiring harness will plug right in. i'll check on those wires for you and try to get back to you this weekend
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    I concur on how to get a check engine (GM just replaced the "choke" light with the check engine light filter) but the source will only be a 1987-1989, as 1990+ is digital speedometer and quite a bit different than the previous years. Any CCC truck should have a donor check engine light as well, but I've never seen the cluster from one of those trucks.

    If you still have access to the donor, take ALL wiring out that was tied into the TBI at all. The ALDL wiring probably runs all the way under the dash to the ECM on the passenger side, assuming the '89 has the ECM in the same general location as most GM vehicles.
     
  4. divorced

    divorced 3/4 ton status

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    I own the donor and still have it. I will keep it until the K20 starts. I will have to look for a gauge set I guess. Thanks guys.
     
  5. fatbob

    fatbob 1/2 ton status

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    Maybe I'm missing something:thinking: , but why not use the check engine/gage cluster from the donor?
     
  6. divorced

    divorced 3/4 ton status

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    The donor is an '89 C1500 2 wheel drive truck, the dash and gauges are completly different than my '79 K20.
     
  7. fatbob

    fatbob 1/2 ton status

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    THATS what I was missing:doah:, but maybe you could use just the check engine lightsocket from the 89 and plug it in the back of the speedo.:dunno:
     
  8. divorced

    divorced 3/4 ton status

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    Maybe, I don't know. Just any orange (or any color) light mounted any where in the dash would be good enogh for me, it doesn't have to be in the cluster. It's just and old pile truck, cosmetics mean nothing.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Easiest thing to do is going to be to find someone with the gm wiring manual for the '89. It's going to be one wire from the ECM, and IIRC, it grounds through the ECM to set the light, so you just supply ignition 12v power to whatever you want to use as a light.

    Again, the wiring manual will let you know which wire, and whether it needs a ground or 12V constant.
     
  10. divorced

    divorced 3/4 ton status

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    Thanks Dorian. I was reviewing in my mind today the things I will need to do for this swap and thought that a complete wiring diagram is necessary. I will go check with our local Chevy dealer, maybe they will make some copies for me, if not I will locate and purchase a manual.

    Another couple quick questions - After I swap, will the engine run well enough without the o2 sensor to get the truck on a trailer so I can take it to the exhaust shop?

    And will everything work ok without the VSS connected? I plan to use my th350 that is currently in the truck.
     
  11. dirtwarrior17

    dirtwarrior17 Banned

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    yes...... mine would run as long as you kept your foot on the throttle. Just enough to keep it from stallin and that was when i had the vacuum lines crossed up.

    you should be able to get it on a trailer without a problem... they don't even kick in until they reach 600 degrees F unless its a heated o2
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    ditto on O2.

    VSS I would fix. Ask those that have run EFI with and without it, and the resulsts are positive. I ran my truck without it for a BIT (too lazy to hook it up to speedo for a day) and didn't notice anything, however, stalling when you lift off the throttle is a very real concern.

    There's a TON of VSS info on here, thirdgen.org, and jagsthatrun.com, so really no reason to post it all back up here.

    Real issue in your case is going to be what the '89 used for VSS? Was it a t-case or tranny mounted as I suspect, with a DRAC? The links in my DRAC post may answer what you need...again, things change, so it's hard to make a blanket statement, but here's what I would *expect*:

    The '89 TBI ECM is probably looking for a 2000PPM (pulse per mile) input from the DRAC. The '8x-89 (VSS used with elecrronic cruise, CCC and TBI for those years) truck clusters all used a cable drive VSS, with a buffer that outputs 2000PPM. That output from the '8x cable drive VSS buffer could then be wired to the ECM VSS wire, and your VSS issues would be solved.

    The ONLY variable is what type of signal the '89 TBI ECM is looking for on the VSS pin.
     
  13. fatbob

    fatbob 1/2 ton status

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    You want wiring diagrams. Here ya go.:thumb:
    http://www.chevythunder.com/index.htm
    Find out what ECM you have and you can click on this page for schematics.
    They have a lot of other info you might be able to use, also.
     
  14. divorced

    divorced 3/4 ton status

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    Nice link, thanks!
     

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