Early 4L80e with a later model ECM - how difficult?

[Daveo91]

I have two threads active right now regarding some tuning issues with my vortec 383 TBI. My 91 3/4 ton, 4x4 Burb has the original ‘7060 ECM and in talking with Dave W, we’re wondering if some of my problems could be related to that ECM. It was a short-lived design and it seems that there wasn’t a huge amount of work on the hacks for it compared to the ‘7427. That and it doesn’t seem like there’s any way to get my WBO2 data fed into it due to lack of an available 0-5V input.

So one possible solution is to convert to a ‘7427, but the early 4L80e Bosch force motor requires periodic cleaning that is controlled by the ECM, whereas the later ones used a Holley force motor that did not require that from the ECM. All the threads I’ve read on this here or elsewhere point to the only solution is to physically modify the tranny to use the later force motor. Is that still the case? No way to modify the ‘7427 to take care of the cleaning? If physical mods required, how big a chore is this? Do it without dropping the tranny? I’ve also read that the early vs. late 4L80e operated at different frequencies as well, so there’s that to consider too.

Any 4L80e experts I’d love to hear from you, thanks!

[THEFERMANATOR]

To run the 7427 there's a few changes that I know you'll have to make. The trans change is you can simply remove the early force motor and install the 94+ style. This will work, but you will have lazy line pressure changes since the accumulator for the force motor will still be in play. You can remove your valve body and use a BB or check ball to block the force motor accumulator to make the line pressure respond quicker, or just run it as is, and it will respond like any other 91-93 4l80e. You will also want to replace/update your internal and external harness if you haven't already done so. And if you have a 4x4, you will have to install a VSSB instead of your current DRAC. The VSSB has a conditioned VSS output that gets sent to the ECM whereas your 91 had the VSS going straight to the ECM. I've heard you can change the flag for the VSS in the programming for the 7427, but VSSB's are cheap, so I would just stay with the OEM set-up to avoid any quirks.

[Daveo91]

To run the 7427 there's a few changes that I know you'll have to make. The trans change is you can simply remove the early force motor and install the 94+ style. This will work, but you will have lazy line pressure changes since the accumulator for the force motor will still be in play. You can remove your valve body and use a BB or check ball to block the force motor accumulator to make the line pressure respond quicker, or just run it as is, and it will respond like any other 91-93 4l80e. You will also want to replace/update your internal and external harness if you haven't already done so. And if you have a 4x4, you will have to install a VSSB instead of your current DRAC. The VSSB has a conditioned VSS output that gets sent to the ECM whereas your 91 had the VSS going straight to the ECM. I've heard you can change the flag for the VSS in the programming for the 7427, but VSSB's are cheap, so I would just stay with the OEM set-up to avoid any quirks.

Thanks much for the info. I thought it was along those lines. I’m pretty much leaning away from this mod now and keep trying to make the ‘7060 work. At least for now while tranny is working well- if I have to go into it for something I may change my mind. And I do have 4wd so makes it even more stuff to do.

I purchased a spare ‘7060 from a member here (on its way). That will allow me to rule out my existing pcm causing any of my issues. And im looking for a used moates AutoProm which I think would allow me to combine the WB output with pcm output for data logging.

[Daveo91]

To run the 7427 there's a few changes that I know you'll have to make. The trans change is you can simply remove the early force motor and install the 94+ style. This will work, but you will have lazy line pressure changes since the accumulator for the force motor will still be in play. You can remove your valve body and use a BB or check ball to block the force motor accumulator to make the line pressure respond quicker, or just run it as is, and it will respond like any other 91-93 4l80e. You will also want to replace/update your internal and external harness if you haven't already done so. And if you have a 4x4, you will have to install a VSSB instead of your current DRAC. The VSSB has a conditioned VSS output that gets sent to the ECM whereas your 91 had the VSS going straight to the ECM. I've heard you can change the flag for the VSS in the programming for the 7427, but VSSB's are cheap, so I would just stay with the OEM set-up to avoid any quirks.

So I remembered something. My tranny is a reman from I think '94. Any chance it has the updated force motor that does not require the software cleaning routine? Is there any way to tell externally or by testing? I took some pics of the name plate and sticker when I had the engine and tranny out.

14397
14398

[THEFERMANATOR]

That appears to be a 93 model if I'm reading it correctly. If it works with a 91-93 ECM, then it is most likely correct as ONLY the 91-93 model 4L80E had the output reluctor installed in a 4x4 4L80E. Otherwise to be certain you have to drop the pan and look at the force motor to see which one it has.

[mihela]

That appears to be a 93 model if I'm reading it correctly. If it works with a 91-93 ECM, then it is most likely correct as ONLY the 91-93 model 4L80E had the output reluctor installed in a 4x4 4L80E. Otherwise to be certain you have to drop the pan and look at the force motor to see which one it has.

My 95 4WD trans has the output reluctor.

[Daveo91]

That appears to be a 93 model if I'm reading it correctly. If it works with a 91-93 ECM, then it is most likely correct as ONLY the 91-93 model 4L80E had the output reluctor installed in a 4x4 4L80E. Otherwise to be certain you have to drop the pan and look at the force motor to see which one it has.

Yeah, I've come to the same conclusion, if they upgraded the trans to the later model at that time they probably would have had to replace the PCM to match. I think it's pretty likely that I have the older FM. Next time I drop the pan I'll check to make sure, but for now I'm going to keep plugging away trying to make the 7060 work. Thanks for info.

[THEFERMANATOR]

My 95 4WD trans has the output reluctor.
No 95 4l80e 4x4 had an output reluctor wheel stock. The hole is there and it may even have a speed sensor installed instead of a dummy plug, but if it's stock, there is no 40 tooth reluctor. ONLY 91-93 4l80e 4x4's had it installed. Many have said they had a 94+ with one until they removed the OSS, and looked inside to find nothing(or the 21 teeth of the adjacent hub). If your 95 has it, somebody put it there other than GM.