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4l80e problems

cuervo

cuervo

Runn'n down a dream!
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I have a 4l80E that has some issues. It's in a 91 2500 sub 4x4.


It starts out in 2nd gear and will downshift to 1st after you press the gas a down a bit. (has 2nd and 3rd gear only).

It also will not shift into OD but I think it's been doing that for some time now.

I did a filter and fulid change.

I've read a few things about cleaning the contacts at the firewall connector and about changing the A Shift Solenoid.

Anyone else have ideas?

BTW: No check engine light. I don't have an OBD1 scanner so I don't know if it's putting out codes.
 
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cuervo said:
BTW: No check engine light. I don't have an OBD1 scanner so I don't know if it's putting out codes.
Click to expand...


AutoZone sells a "key" for pulling codes for a couple of bucks, I would suggest buying to check with.

Fwiw, my old 91 crew cab had some 4l80e shifting issues that I almost never found. Mine turned out to be an injector wire pinched under the air cleaner. The resulting ground cause it to go into some sort of limp mode with converter lock up enabled 100% of the time. It felt like it was starting off in 2nd and felt very sluggish. However, o/d functioned and was not effected (other than lock up on constantly).
 
nvrenuf said:
AutoZone sells a "key" for pulling codes for a couple of bucks, I would suggest buying to check with.

Fwiw, my old 91 crew cab had some 4l80e shifting issues that I almost never found. Mine turned out to be an injector wire pinched under the air cleaner. The resulting ground cause it to go into some sort of limp mode with converter lock up enabled 100% of the time. It felt like it was starting off in 2nd and felt very sluggish. However, o/d functioned and was not effected (other than lock up on constantly).
Click to expand...

I'm not sure if you can get transmission codes like that.
 
if i recall 91-93 had bad tranny valve body harnness. thay offered a update kit to fix this problem.

i have 96 and newer 4l80 stuff no help on your 91 tho.
 
Trans codes can be pulled with the code key, the engine and trans use the same ecu. If you get any codes post them here, I still have my '91 GM manuals.
 
They = GM

Look for a big bundle of splices in the harness a couple of inches outside of the trans case. If you find that you should have the updated valve body harness.
 
nvrenuf said:
They = GM

Look for a big bundle of splices in the harness a couple of inches outside of the trans case. If you find that you should have the updated valve body harness.
Click to expand...

Wow, so the new harness needs a new pigtail on the end of that has to be spliced in?
 
nvrenuf said:
AutoZone sells a "key" for pulling codes for a couple of bucks, I would suggest buying to check with.

Fwiw, my old 91 crew cab had some 4l80e shifting issues that I almost never found. Mine turned out to be an injector wire pinched under the air cleaner. The resulting ground cause it to go into some sort of limp mode with converter lock up enabled 100% of the time. It felt like it was starting off in 2nd and felt very sluggish. However, o/d functioned and was not effected (other than lock up on constantly).
Click to expand...

Mine was acting up due to a bad coil. It would shift into all the gears really sluggishly and the TC would lock up at random and going down the highway no matter the speed it constantly lock and unlock.

All from a bad coil.. it was shorting out on the intake, when the truck was running you'd hear snap-snap-snap noise and could see little sparks :eek1:

No check engine light either, never bothered to check the codes though.. you can just do the paper clip method though.

Mine has the updated harness and all of 60k on a GM crate 4L80E that was installed by the dealer in 1998.
 
cuervo said:
Wow, so the new harness needs a new pigtail on the end of that has to be spliced in?
Click to expand...


Yes.

And the transmissions internal harness has to be updated as well.

The original connector has a bolt through the middle holding it to the tranny. The updated connector just "clicks" on.

Tommy
 
TommyM said:
Yes.

And the transmissions internal harness has to be updated as well.

The original connector has a bolt through the middle holding it to the tranny. The updated connector just "clicks" on.

Tommy
Click to expand...

Well, mine has the clip on model already.

I took it by a shop yesterday and they check for codes.

It was giving

27, 33, and 63

Which relates to the Force Motor, Pressure Switch Manifold and Overdirve Ratio.

So the internals are fine, it's just electrical issues, IE switchs and such.

That being said, the low line pressure which makes the tranny default to second gear at take off is from the pressure switch manifold and the force mainifold. The pressure switch also defaults so the TCC is not working causing the no overdrive.
 
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