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4l80e help

W

Wally tavera

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Location
Oregon
1991 chevy suburban transmission shift hard 1st and 2nd no lock up in overdrive let I sit for 30 min drive again everything work good can drive for hours until I shut if off and start it up and and will act back up again. And this transmission was rebuilt 1500 miles ago.
 
Sounds to me like either a loss of prime issue when it sits for extended periods, or some electrical issues. I remember there being a problem with the early 4l80e controllers being set to sensitive to loss of prime, and it causing limp mode on a cold start. Drive it through the gears to reprime the trans, shut it off, and when you restart it everything was fine. I'll have to try and search to find it again.
 
THEFERMANATOR said:
Sounds to me like either a loss of prime issue when it sits for extended periods, or some electrical issues. I remember there being a problem with the early 4l80e controllers being set to sensitive to loss of prime, and it causing limp mode on a cold start. Drive it through the gears to reprime the trans, shut it off, and when you restart it everything was fine. I'll have to try and search to find it again.
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I've been looking through all the electrical and I replaced all the sensors. checked the throttle position sensor it seems to be getting all the right volts it needs in there I'm just don't know what to do with it like I said it runs and drives fine down the road as soon as I shut the ignition off turn it back on then it goes into a hard shift and then I shut it off wait a few minutes again maybe 30 and then it works just fine
 
Drain fluid and save. Pull the pan and double check the lower harness is not pinched under the pan gasket.

Just rebuilt- WARRANTY?
 
Will L. said:
Drain fluid and save. Pull the pan and double check the lower harness is not pinched under the pan gasket.

I pulled the pan and I looked at the wiring and I we changed all the solenoids again to make for sure that it wasn't one that just decided to go bad and I still have no check. I bought the truck from some guy that had it done a year ago and he showed me the paperwork and only have 1500 miles when it start acting up again on him.
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snarl95 said:
Pull the connector on side of trans and see if there is fluid in the connector.
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There was some oil in there once before I sprayed it out with the electrical cleaner
 
Ask the computer "why"? Should be a code in it.
 
Well I reset my computer drovp my vehicle around and finally said just one code out of the whole system it shows 85 I think that is the prom error code what is that this thanks
 
Code 85 is undefined ratio error, meaning the actual measured gear ratio by the controller is different than what it should be by to large a margin. I'm still digging for that tsb as I could have sworn code 85 was the one it caused, and the fix was a prom change. But I also found this bulletin that applies to early 4l80e's that have recently been rebuilt.
https://www.google.com/url?sa=t&sou...FF5kv3wPPlcbTfcFg&sig2=BnWyw-6BKdWUuYYJMT-7og
 
So should I change the prom and see what the heck happens I mean that's the only thing I could see it could be causing the havoc on the transmission no other codes come up
 
Problem is finding one. GM has long since discontinued stocking them last I checked, and just finding part numbers is getting difficult.
 
Put a scanner on it and see what the speeds are . The book also tells you to check the PSM ( pressure switch manifold ) , this lets the ECM know what gear is selected .
 
New doesn't mean good. You NEED to get a scanner on it and watch it when it does it to see what it is doing. Otherwise you're simply guessing at the problem.
 
Personally I would not reuse a pass thru connector if there was ATF coming out of it . Clean it once or to get you home but not in the long run . They have been redesigned . Your problem sounds like an electrical issue , than mechanical , which is why you need a scanner . Grounds can also be a problem .
 
Seems to be a very common issue on DB2 with 4L80Es. My old 93 to the same thing. I never did fix it before selling it.
 
i converted mine to manual valvebody. it wasn't shifting out of 1st. figured it was a wiring issue and wasn't able to find it. also have TCC manual lockup.
only problem is it needs a reverse lockout shifter and will need mounted on the floor.
 
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