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Thread: Hello- wild situation with a 4l80E need opinions

  1. #1
    Carb and Points!
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    Hello- wild situation with a 4l80E need opinions

    Hello everyone! This is my first post and I hope I’m in the right area. What I have is a buddies 93 c3500. Brought to me with a 68 code for slip. Checked all solenoids and basic stuff. Long story pulled trans and sent off to have rebuilt. What I realized after is that it’s a late model 4l80e(cooler lines in front and back on trans and 5 bolt bell housing). I talked to a very well known trans guy in Oregon and he said you can run this trans with the PROM on a 93 with that cleaning cycle and the lower freq. solenoid.
    I am currently at a stop point. I have the rebuilt trans back in the truck and still getting a 68. I have replaced ignition control module, both VSS (input and output, it’s a 2wd dually), it has the updated wire harness on both truck and trans side. I’m getting good readings on my tech 2 for all basic inputs ie map, tps, vss, solenoids. The weird part I am seeing is with the RPMs, I have scoped both input sensor and what I think is the correct input for ESS (off dizy) I scoped all 4 wires off that and they are all showing a wave going up and bouncing about 3 times with about a 1v difference and then back down( not sure if this is a good wave for PCM. The wave form for ISS is a standard wave and very consistant. I am showing at idle a 300 rpm difference between ESS and ISS and the range grows the higher rpm is. The computer will command 4th but I never feel it kick and don’t see TCC lock up. If I force TCC lock up when pcm commands4th I get a shudder and about 500 on the TCC slip pid. This has me puzzled because one it’s not the original trans and not sure if this is all caused by the PROM. Any suggestions would be greatly appreciated! I love learning new things but I’m at my wits end with this one. I’m fixing to take the truck back to the trans shop that rebuilt it because I am leaning towards trans issue.
    what do yall think?
    thank you in advance
    Last edited by Plehne; 11-27-2023 at 05:34 AM. Reason: Incorrect info

  2. #2
    Super Moderator dave w's Avatar
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    Would I be correct thinking the 93 C3500 has the 16147060 PCM?

  3. #3
    Carb and Points!
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    Yes sir and it has BAMP on there if I’m not mistaken. I haven’t got into the dark arts y’all are into but was hoping you might have some insight.
    Last edited by Plehne; 11-28-2023 at 01:48 AM.

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  5. #5
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    Thank you but I was hoping for more of a prom question if the prom from a 93 would run a late 4l80? Itís getting ready to go back to the trans shop that rebuild it.

  6. #6
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    Welcome to the forum.

    This one sounds interesting. Your diagnostic tests seem to have created as many questions as answers. First and foremost is that it appears the ECM believes it is seeing greater than 200 rpm difference between engine speed and input shaft speed. It sounds like you've attempted validation testing to confirm the issue but the results were not helpful. Here's a few more answers.

    1) The four wires from the distributor are labelled REFerence, EST, Bypass, and signal low. REFerence is the white wire and it provides a square wave signal from the module to the ecm. EST is the purple / white wire that carries the timing signal from the ECM to the module. EST is also a square wave when the ECM is commanding timing. The Bypass wire is tan / black and you will read 5V on that wire when the ecm wants to control timing or zero volts when the ecm does not want to control timing. Black / red is signal low, a dedicated ground between the module and ECM. The wave you're describing sounds like ignition secondary pattern. Ignition secondary should not show up on the wires between ECM and distributor.

    It is possible to calculate rpm using the measured time between the start of two of the square wave pulses then doing math. 720 / number of cylinders / time measured * 60 should give RPM.

    With the TCC locked I would expect to see the same RPM between the engine and the ISS. With TCC unlocked I would expect to see the difference between ISS and RPM vary from very high under load to almost zero when coasting. If I suspected actual slip I might try locking the TCC then watching for the difference in RPM between ISS and engine to behave somewhat like unlocked TCC behavior: more slippage under load and nearly zero when coasting.

    We used to have a guy here that had a bunch of 4L80E knowledge. I haven't seen him post in a while. But as I remember the new "black" force motor was introduced into all 4L80E in 1994 while older models used the "silver" force motor. I do not have a chart that links your EPROM code to force motor types, but you need a prom that provides 614 Hz control of the force motor.

  7. #7
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    How hard is it to burn or re program the PROM? I have fiddle farted around on forscan with fords but that’s obd2. And thank you for the post! It gave me some different things to think about. That was my big worry that the deference between force motors. Having a 400mhz difference between the two(not knowing much about the operational theory) but that seems to be a large gap. I’m almost wondering if I shouldn’t get a new prom before taking back to the trans guy.

  8. #8
    Super Moderator dave w's Avatar
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    The original 16147060 computer uses an EPROM chip which requires an Ultraviolet Light to erase. A common alternative to the EPROM chip is an EEPROM chip which is Electronically Erasable that eliminates the requirement for an Ultraviolet Light.

    An adapter board allows using the EEPROM chip in the 16147060 computer: https://boostednw.com/chips-and-adpt...memory-adapter

    One possible option to program an EEPROM chip is a programmer from: https://boostednw.com/boostednw-burner-programmer

    Pictures show an optional ZIF socket installed on the adapter board.

    G1 Adapter Install_01.jpg

    G1 Adapter Install_02.jpg

    ZIF.jpg
    Last edited by dave w; 11-28-2023 at 04:51 PM.

  9. #9
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    That would be doable I think. One more question, could I possibly order a new ecm from the parts store say for a 94 with matching engine/trans? This is a farm truck so not critical that I keep oem parts. I think this would do away with the clean cycle and operate the 614htz solenoid.

  10. #10
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Plehne View Post
    That would be doable I think. One more question, could I possibly order a new ecm from the parts store say for a 94 with matching engine/trans? This is a farm truck so not critical that I keep oem parts. I think this would do away with the clean cycle and operate the 614htz solenoid.
    The Quick Answer is NO.

    The 16147060 has two tan computer connectors.

    The 1994 computer has One Blue computer connector and One Red computer connector.

    With some computer connector re-wiring skills, the conversion to the 94 computer is possible.

    7060.jpg

    94.jpg

  11. #11
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    Quote Originally Posted by dave w View Post
    The Quick Answer is NO.

    The 16147060 has two tan computer connectors.

    The 1994 computer has One Blue computer connector and One Red computer connector.

    With some computer connector re-wiring skills, the conversion to the 94 computer is possible.

    7060.jpg

    94.jpg
    The wiring doesn’t bother me much but if the prom has to be changed that might be the easier option for me. This is just an area I have never been before as far as prom and non oem equipment not being plug and play.

  12. #12
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Plehne View Post
    The wiring doesn’t bother me much but if the prom has to be changed that might be the easier option for me. This is just an area I have never been before as far as prom and non oem equipment not being plug and play.
    It seems unlikely the PROM or Computer would be the root cause for error code 68.

    It seems unlikely the transmission would be rebuilt with an incorrect force motor, when the correct model year was specified.

    Swapping the 16147060 Computer and / or PROM is a troubleshooting option.

    Gearhead-efi 16147060 information page: http://www.gearhead-efi.com/Fuel-Inj...Information-85

  13. #13
    Super Moderator dave w's Avatar
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    Chip file or Binary file or .bin file "BAMP" attached.
    Attached Files Attached Files

  14. #14
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    Thank you much for all your input! I will keep you posted on the issue maybe it will help someone else down the road, I have a couple options and not sure exactly what way I’m going to head yet.

  15. #15
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    Quote Originally Posted by 1project2many View Post
    1) The four wires from the distributor are labelled REFerence, EST, Bypass, and signal low. REFerence is the white wire and it provides a square wave signal from the module to the ecm. EST is the purple / white wire that carries the timing signal from the ECM to the module. EST is also a square wave when the ECM is commanding timing. The Bypass wire is tan / black and you will read 5V on that wire when the ecm wants to control timing or zero volts when the ecm does not want to control timing. Black / red is signal low, a dedicated ground between the module and ECM. The wave you're describing sounds like ignition secondary pattern. Ignition secondary should not show up on the wires between ECM and distributor.

    Just want to nip a possible point of confusion for anyone new to the GM ignition...

    You have your REF and EST wire colours backwards. Purple/White is the REF wire, and send the RPM reference pulses, AKA "DRP" (Distributor Reference Pulse) to the ECM and the white wire is the return from the ECM to the ICM that controls the actual timing.
    The man who says something is impossible, is usually interrupted by the man doing it.

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