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Thread: Pinout adapter?

  1. #1
    Electronic Ignition!
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    Pinout adapter?

    I have a 91 g20 van that I would like to put a 4L80 into.... in place of the 700r4
    The current ECM is a 7747 and It looks like I need a 7427 ECM to run the 4L80...….
    Assuming that the pinouts are always the same on every 7427 and that all 7747 units would share the same pinouts...…. I'm wondering if anybody manufactures a set of adapter plugs that would fit the 7427 ECM and allow the existing van harness to plug into it and operate properly (?) ..... This harness adapter would also need the extra wiring out of the 7427 to run the transmission.....

    If plug-n-play products like this exist and work, I'm an interested buyer....

    I mis-spoke earlier..... My ECM in the 91 van is a 7747...
    Last edited by AzDon; 01-07-2019 at 10:58 AM.

  2. #2
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    Hi Don,

    From time to time there have been ambitious folks that have made a run of adapters like what you describe. I've seen them built for installing an 88-92 truck computer into older vets, to replace the 86-89 Vette computer with a 90-91 model, and even a few to upgrade the 88-91 trucks. Vans never get any love.

    You might find an adapter but here's my thought: None of the wires to control the 4L80E are present in your harness. Even with the adapter you still need to add them. So maybe the easiest answer is to locate a complete harness from a 4L80E equipped van? I know from working with a fleet of school buses since 2003 that the one ton cutaway chassis vans usully came with 350 / 4L80E. If you could find one used then you'd get all the parts you need for your swap.

    Barring that, you can buy a used ecm and a couple of connectors and make a harness. It's something you can do in the house or garage, sitting at a table or bench in comfort. You don't need the same number ECM as what's in your van because the ECM plugs for many of the older TBI vehicles are the same. I just searched Ebay for GM TBI ECM and came up with a pile of computers (there's a 1227746 for $20) and the red and blue connectors for the 1227727 (one seller has them listed for $12.95 with free shipping). I usually make a chart to help keep track of the changes and to note anything that's different such as when GM has added or deleted circuits of features over the years. It can take a few hours to build a harness but it does save a bunch of time when you're ready to install the ecm.

  3. #3
    Super Moderator dave w's Avatar
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    There are numerous options to convert a 700R4 to a 4L80E!

    Possibly the option of using the 16197427 as a standalone 4l80E controller is worth thinking about? Using the 16197427 as a standalone controller is a simple and low cost option. Using the 16197427 as a standalone controller allows keeping the 1227727 TPI computer EXACTLY like it is!
    Basically the 16197427 PCM will need the flowing inputs to operate a 4L80E:
    Ignition On / Start power
    Battery Positive
    Ground / Battery Negative
    TPS (piggy back the TPS signal from the 1227727)
    Distributor Reference Pulse (DRP) (piggy back the DRP from the 1227727)
    VSS ( 2000 Pulses Per Mile ) --- Using a calibrated DRAC
    ISS
    4L80E Pigtail with VSS & ISS wiring
    Custom PROM chip

    Piggy Back = Splice into the 1227727 wiring to "share" the wiring with the 16197427.

    dave w

  4. #4
    Fuel Injected! Queencityspeed's Avatar
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    AzDon,
    I could build you a custom adapter harness the adapter harness if your interested.

  5. #5
    Electronic Ignition!
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    Quote Originally Posted by 1project2many View Post
    Hi Don,

    From time to time there have been ambitious folks that have made a run of adapters like what you describe. I've seen them built for installing an 88-92 truck computer into older vets, to replace the 86-89 Vette computer with a 90-91 model, and even a few to upgrade the 88-91 trucks. Vans never get any love.

    You might find an adapter but here's my thought: None of the wires to control the 4L80E are present in your harness. Even with the adapter you still need to add them. So maybe the easiest answer is to locate a complete harness from a 4L80E equipped van? I know from working with a fleet of school buses since 2003 that the one ton cutaway chassis vans usully came with 350 / 4L80E. If you could find one used then you'd get all the parts you need for your swap.

    Barring that, you can buy a used ecm and a couple of connectors and make a harness. It's something you can do in the house or garage, sitting at a table or bench in comfort. You don't need the same number ECM as what's in your van because the ECM plugs for many of the older TBI vehicles are the same. I just searched Ebay for GM TBI ECM and came up with a pile of computers (there's a 1227746 for $20) and the red and blue connectors for the 1227727 (one seller has them listed for $12.95 with free shipping). I usually make a chart to help keep track of the changes and to note anything that's different such as when GM has added or deleted circuits of features over the years. It can take a few hours to build a harness but it does save a bunch of time when you're ready to install the ecm.

    The adapter I visualize would have a sub-harness coming out of it for the transmission...….Buying a standalone controller is probably a more sanitary solution than splicing into a working wiring harness.... It's only money, right?


    I just figured that with all the confusion over wire colors and the names and usage of different utilities...….That IF the pinouts are always the same for a particular ECM......That going from pinouts at your preferred ECM to pinouts in your original ECM's plug would be a foolproof plug-n-play...

    A huge negative when looking at used c1500 trucks and g-vans is the POS 4L60 and 700r4 transmissions.....Those transmissions are not really towing transmissions and are usually used up between 80k and 140k miles and are often the reason people are "offing" a vehicle that otherwise is only half used-up....In times past (the old days) folks would simply swap a t400 in place of their scattered t350 and head on down the road.... What has changed is that every major change now comes with a new and different harness and ECM and NO HELP from the OEMs to aid in our success in interfacing to the next technology...…They keep their tech secret so that anybody that wants to benefit from it (other than buying a new vehicle) has to pick through and reverse-engineer everything to uncover the similarities and differences and risk burning everything down through trial-and-error.....

  6. #6
    Super Moderator dave w's Avatar
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    I've made computer adapters ('7747 TBI computer to '7427 TBI computer), see link: http://www.gearhead-efi.com/Fuel-Inj...7-Adapter-Plug

    This plug-n-play adapter could also include a 4L80E pigtail.

    dave w

  7. #7
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    A huge negative when looking at used c1500 trucks and g-vans is the POS 4L60 and 700r4 transmissions.....
    Have you no source for the one-ton cutaway chassis vans? Beginning in model year 91 those usually came with the 4L80E.

  8. #8
    Electronic Ignition!
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    Custom made sounds expensive, but a limited market probably keeps stuff like this out of mass production.... What might an adapter harness like this cost to have made?

  9. #9
    Super Moderator dave w's Avatar
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    Some listings on Ebay for parts.

    16197427 Connector with pigtails.
    https://www.ebay.com/itm/1993-95-GMC...8eb:rk:16:pf:0

    16197427 Computers
    https://www.ebay.com/sch/i.html?_fro...97427&_sacat=0

    1227747 Computers to harvest parts from:
    https://www.ebay.com/sch/i.html?_fro..._odkw=16197427

    4L80E Pigtail (needs to much longer! Link is for pricing)
    https://www.ebay.com/itm/4L80E-Conne...zRg:rk:22:pf:0

    dave w

  10. #10
    Fuel Injected!
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    Not sure why you would want to mess with an adapter.....

    I have repined numerous TBI systems to the later PCM. The first time I ever attempted the job it took me a few hours of research to find the wiring diagrams, a couple of hours to match up all the connections, and with the spread sheet I made, took me about 1 hour to swap out the 7747 connectors for the 7426 connectors. I labeled each wire with 7747 pin location with masking tape and a marker and moved them one at a time to the 7427 connectors.

    The 4L80E takes 15 wires to run, 12 of which pin into the ECM, 2 go to the VSSB/DRAC and one connection to keyed 12V power. You could add a sub-harness to the existing harness very easily.

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