Hello- wild situation with a 4l80E need opinions

[Plehne]

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

[dave w]

Would I be correct thinking the 93 C3500 has the 16147060 PCM?

[Plehne]

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.

[dave w]

https://www.justanswer.com/chevy/3ermq-92-chevvrolet-truck-4l80e-transmission.html

[Plehne]

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

[1project2many]

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.

[Plehne]

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.

[dave w]

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-adpters/GM/g1-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.

19572

19573

19574

[Plehne]

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.

[dave w]

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.

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[Plehne]

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.

19575

19576
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.

[dave w]

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-Injection/showthread.php?317-16147060-PCM-Information-85

[dave w]

Chip file or Binary file or .bin file "BAMP" attached.

[Plehne]

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.

[Six_Shooter]

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.

[Six_Shooter]

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.

When you order ECMs from the parts store they don't come with the MEMCAL or PROM, so you would still need to source that and/or program your own EEPROM to be successful.

That being said, some of us have horded ECMs and might have something that might work for you.

I will have to look into this a bit more, but I don't see why the 7060 ECM won't work for you. I tune a friend's stable of cars and 4L80Es seem to end up in all of them and haven't had any issues like you are experiencing, though he tends to use earlier 4L80s with the one piece cases but both front lube and center lube, depending on what he can get his hands on. AFAIK, the internal controls haven't really changed between the update in 1994 and the two piece cases.

[1project2many]

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.

You are correct, sir. Thank you for the correction.

[Plehne]

When you order ECMs from the parts store they don't come with the MEMCAL or PROM, so you would still need to source that and/or program your own EEPROM to be successful.

That being said, some of us have horded ECMs and might have something that might work for you.

I will have to look into this a bit more, but I don't see why the 7060 ECM won't work for you. I tune a friend's stable of cars and 4L80Es seem to end up in all of them and haven't had any issues like you are experiencing, though he tends to use earlier 4L80s with the one piece cases but both front lube and center lube, depending on what he can get his hands on. AFAIK, the internal controls haven't really changed between the update in 1994 and the two piece cases.
I really appreciate it. I ended up talkin with a guy about my situation and back in the woods he had a 93 4l80 so the trans shop is getting the truck back and I think he wants to try and fix it but might end up bartering the fresh late 4l80 in exchange for rebuilding the correct trans for that truck. I will keep you posted. I haven’t completely ruled out a smoked ECM. Question though if I remember correctly I was getting the same wave form on all 4 wires from the ICM. But getting a RPM with no drop outs have you ever looked at the wave forms from that?

[1project2many]

I'm unsure what you're asking. This picture shows waves similar to what the GM REF and EST will show if scoped while the engine is running. The top signal is from the pickup coil to the ignition module. The two bottom signals represent REF and EST.



If you are seeing a different signal on EST or REF then you may be seeing noise from the ignition system or another component.