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Thread: 4l80 swap into 454TBI C3500 2WD

  1. #1
    Electronic Ignition!
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    4l80 swap into 454TBI C3500 2WD

    A friend of mine has a 91 or so C3500 with the 454 and a TBI setup running what he told me was a 700-R4. The transmission was supposedly rebuilt by a company that had done a Tranny flush improperly. Now it hardly shifts and runs like crap even though it doesn't have many miles on it.

    I managed to get a deal when I was looking for a basic motor to get my 94 suburban running. 350 TBI motor and 4l80 with wiring harness and ecu and I was looking at putting the 4l80 into his truck. I figure I would have to do some combining of wiring harness' but that doesn't bother me. My concern is that the stock computer won't run the tranny and the ecu that came with the tranny won't run the engine properly.

    The ecu that came with the transmission is a 7060 unit and I am not sure yet what came with truck. I will find out, but haven't had the time to get out to his house and pull the glovebox. Either way I figure it is easier to reprogram for the engine instead of trying to make his ecu work with the tranny. I would like to avoid buying a stand alone controller especially since I believe this was a factory option.

    I'm not looking for anything other than a stock tune as nothing has been done to the engine or tranny that I know of. He isn't looking for anything other than a reliable vehicle. Is there a good vendor to buy a chip off of or is there someone here that would like to make my life easier and burn me one?

    If I'm missing something else please feel free to chip in

    Thank you

  2. #2
    Super Moderator dave w's Avatar
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    I would need the exact ECU part number of the 91 or so C3500 to be accurate on what options are available.

    Without the exact ECU part numbers in the the post above, maybe there is the option to re-pin the 91 or so C3500 ECU for the 7060 ECU, add the 4L80E wiring, and then burn a custom chip to make everything work.

    dave w

  3. #3
    Fuel Injected! brian617's Avatar
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    The 91 c3500 with 5.7 or 7.4 only had the option for a 4L80e. Count the number of transmission pan bolts to be sure it hasn't swapped.
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

  4. #4
    Electronic Ignition!
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    Quote Originally Posted by brian617 View Post
    The 91 c3500 with 5.7 or 7.4 only had the option for a 4L80e. Count the number of transmission pan bolts to be sure it hasn't swapped.
    I was hoping that might be the case, I haven't seen the truck in about 3 years (He was a previous boss and I work somewhere else now) I asked him to send me some pics of the tranny pan and get the numbers off of the ecu, but his wife went in the hospital yesterday, so he has bigger things on his mind...

    I really appreciate the responses

  5. #5
    Electronic Ignition!
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    He finally got back to me, and he does in fact have the 4l80. Thank you for helping

  6. #6
    Super Moderator dave w's Avatar
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    91 was was the first year for the 4L80E and '7060 computer.

    I see a couple options:
    1. Completely re-pin the '7060 that is currently in the truck to use the 1993 computer, making sure the 4L80E wiring is correct (or add a new 4L80E harness) for the 1993 transmission.

    2. Add the 93 computer to control the 93 4L80E only. The 93 computer will need the following signals to operate a 4L80E: VSS, TPS, CTS, and RPM (DRP). You could leave the original 4L80E connector unplugged, and add a new 4L80E harness from the 93 computer. A custom chip is also needed for the 93 computer. You could solder splice the needed wiring for the 93 computer from the 7060 harness.

    dave w

  7. #7
    Fuel Injected!
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    If he already has a 4L80E in the truck , simply swap the transmission.

    Worst case senerio is the 1991 truck has the old 4L80E plug held to the transmission by a single bolt in the center and your transmission has the updated snap on plug. There are wiring differences that will have to be addressed if this is the case but still a bolt in swap seeing's as you said he actually has a 4L80E.

    Wiring for both style plugs , click to enlarge : Attachment 8844

    If both transmissions have the early bolt on plug , swap the trans and go.

    TOM
    1994 3500 Dually , 502 (509) , 264HR , Edelbrock MPFI , PFI '7427
    2006 Forest river-Sierra 37' 5th wheel
    1999 Astro Van, L31 Vortec , 4x4 conversion
    1994 Pontiac Sunbird "Work ride"
    1993 K-3500 "Ex-diesel" 454/4L80E - '7427
    1992 454SS "Eh Stock" , Blower & '7427 swap .
    1992 S-10 434 SBC/Tremec - '7427
    1984 S-10 , SAS, 496/700R4/205 , D44/14BFF -'7427
    1980 Z-28 454/700R4
    1977 Olds 98 Regency 403/700R4

  8. #8
    Electronic Ignition!
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    I finally got into that yesterday, He did in fact have the old style plug and the new transmission had the updated one. Thank you Nasty-Z for the wiring diagram. Everything bolted up without a problem and the wiring took about another 20 minutes to go through.

    Transmission works perfectly and shifts through all gears as it should.

    I appreciate all of the advice and willingness to help

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