Researching 4L80E to NV4500 Transmission Swap

[trbankii]

I’ve never been much of a fan of automatic transmissions. That largely comes from driving my parents’ 1974 Peugeot station wagon as a teen. I’ve never personally owned a vehicle with an automatic until purchasing the 1994 Yukon in my signature (you can find more details about it HERE). I’ve always liked these two-door SUVs and found one at a price I couldn’t pass up - but I’m pretty sure they never came with a manual transmission.

Half a year of driving it hasn’t warmed me up to the automatic any more, so I’m looking into swapping an NV4500 into it. The first issue I run into is that of the ECM.

On the one hand, I see information like that from this site: The Novak Guide to the GM 4L80E Automatic Transmission

All 4L80E transmission use electronic controls; typically from the Powertrain Control Module. […] The Transmission Control Module (TCM) is an adaptive learning, computer integrated into the valve body of the transmission and communicates with the Engine Control Module via the onboard vehicle CAN bus network. This is both a return to and a departure from previous automotive control systems in the industry in that earlier electronic transmissions used a separate control module, later to be integrated into the Engine Control Modules which were thus termed Powertrain Control Modules. Now, the high-speed CAN network allows a high rate of data sharing between the units to achieve a collaboration between both engine and transmission functions.

(highlights mine)

But then I’ve also seen information such as this post: Transmission swap to NV4500 This is how I did it

My truck is a 99 K3500 6.5td Crew Cab. […] Anyway several people have asked me for details on my trans swap so I thought I would post it so that others could get the info.

I got my NV4500 from a 4x4 accessories company out of Alabama that I found on the internet. They were easy to deal with and I got a brand new NV4500 for $1910 delivered. This was not much more than I could get a rebuilt for.

My bell housing, single mass flywheel, through out brg, concentric slave cylinder and master clutch cylinder came from another diesel page member that only had a 6k miles on these parts. I gave $450 delivered for this. My other option I was considering on these parts was to buy a new clutch from Kennedy or Heath which when I checked one of them had the clutch and flywheel parts for $384. The rest of these parts I was trying to find from a salvage yard but manual parts are hard to find.

I had to buy the clutch pedal and bracket from a local dealer that gives a substantial discount on parts. These cost me about $100. The pedal, master, slave and bracket has to come from a 97 or newer. The older ones are a different style.

I got the shifter stick and boots from a salvage yard for about $20. They were from an early 90

(again, highlights mine)

The one thing I notice is no mention of computers… Even with a newer OBD-II truck.

So, my question is whether the 4L80E in my ’94 Yukon is “talking” to the ECM or not? If the 4L80E is just separate, swapping it out for the NV4500 should be a “mechanical” project. But if the ECM is going to be “confused” when the 4L80E disappears, then the project becomes an “electrical” one and the ECM will have to be be reflashed with the programming for the manual transmission or swapped for one from a manual transmission truck.

Can anyone answer which way it is? Or point me in a direction to get the information I need?

[Edahall]

I may be wrong but I believe it's the 4L80E that becomes confused if disconnected from the ECM.

I've got a 1996 2 door Tahoe with an NV4500 swapped into it. A few things to watch out on these transmissions is the synchros going out often from the wrong type of oil used. Another thing is the 5th gear nut falling out but usually from a high torque, low rpm engine. Overall, I'm like this transmission but the gear spacing is pretty wide if you're going to use it for towing.

[trbankii]

I’ve got an NV4500 in the K2500 and am pretty familiar with its idiosyncrasies. The “mechanical” part of the swap doesn’t worry me too much - just the electronics. So the 4L80E “missing” the ECM (such as in a mechanical injection swap) isn’t a problem for me. I’m just concerned about the ECM wondering where the 4L80E got to…

[Edahall]

I might be wrong but without the 4L80E in there, the check engine light might illuminate. That would be a concern if inspection in your area requires the CEL to be off.

[trbankii]

We do have annual inspections here, so a CEL would be an issue that would need a resolution.

Any idea where the connection between the transmission and the ECM would be? Would it be a plug into the ECM? Or a connection in the wiring harness someplace?

I wouldn’t expect the 4L80E to work properly if I unplugged things, but I could see if the CEL comes on or if any codes are set.

[Edahall]

There should be a connector that plugs into the transmission itself. However, the CEL may not show up until it is being driven and only under certain driving conditions. The ECM monitors torque converter slippage and it'll throw a code when it notices the converter not unlocking.

The fix is to find an ECM out of a manual transmission truck with the same engine and same year. Ebay would be where I would start looking.