4l80e problem with M1152

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joeberg
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4l80e problem with M1152

Post by joeberg » Mon Jun 07, 2021 12:06 pm

I have an M1152 with about 10k miles on it. The transmission is slipping and it was throwing code 74 (input speed sensor). I traced that problem down to a badly built connector (connector pin wasn't making contact). I rebuilt the connector and resolved the TISS issue, but based on how bad the connector was, I suspect it is likely that this truck has been running without an input speed sensor connected since it was built. I changed the transmission fluid and filter and there weren't any major metal particles in the pan. There could have been a slight burnt smell to it, but barely. It seems to have low power in all gears and can barely make it up some hills in my neighborhood (its not in limp mode and will change to all gears).

My question for the experts is would running without a TISS for a long period of time likely cause an issue and if so, what is the most likely problem caused from it? I have read in other places that the HMMWV doesn't even use the TISS, but obviously the TCM checks for it. I am still troubleshooting, but curious what problems the disconnected TISS could cause if any?

I have a couple of spare transmissions, but I don't want to switch them out unless its really necessary.

thanks,

Joe


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Re: 4l80e problem with M1152

Post by Retired War Horses » Sat Jun 12, 2021 6:47 am

Hmmwv uses the TOSS, not TISS...have you checked your turbo charger and checked for a collapsed catalytic converter?
I’ve had both these issues at some point on these turbo trucks.
Check the impeller while it’s running and see if it’s turning...if so, drop the turbo down pipe and run without to eliminate the catalytic converter
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joeberg
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Re: 4l80e problem with M1152

Post by joeberg » Sun Jun 13, 2021 3:12 pm

RWH, you were exactly right. I disconnected the exhaust pipe on the turbo and it was like night and day. Removed the cat (after confirming the exhaust wasn't clogged) and I now have tons of power and am getting the turbo whistle. I will get a pipe to replace it tomorrow. This problem has been giving me fits. Thank you!

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Re: 4l80e problem with M1152

Post by Retired War Horses » Sun Jun 13, 2021 4:32 pm

Glad to hear it, I’ve been having this odd issue on the turbo trucks, I’ve been deleting the CAT on all my trucks
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