4L80E In and out of Limp mode

[Jrgunn5150]

Truck is a 98 Sierra K2500 8600 GVRW. Previous owner says the trans was rebuilt, it was certainly R&R'd.

Fluid is clean, and I have all 4 gear's as well as reverse. I just got it going, more than around the block today. So the problem is, it's in limp mode, but not always.

The gear indicator in the dash goes on and off as well, the linkage is clearly incorrectly adjusted, as I can engage OD in the indicated Neutral postion. When the indicator is lit, and in "Neutral", the trans shifts as I would expect a 4L80E with a kit to shift, firmly, not harshly, into 2nd under 20 MPH, etc in OD just over 50. Occasionally, driving down the road, the indicator light will go out, the truck will buck hard out of OD, and be in third unlocked.

I have a P0102, as well as a rear O2 code showing pending. The cat is currently in place.

My plan this weekend it to disconnect everything, clean it, reinstall it, see if I can get the transmission cable adjusted properly, clean the ground's up and verify that they are there, dielectric grease all the wiring at the trans.

Does anyone have any other insight or input into thing's I should look at here? I beleive the trans probably was rebuilt, and most likely correctly, I just think they botched the installation.

 

[dave_erald]

I would be scrutinizing that PRNDL switch on the side of your trans. If someone tried to disconnect the electrical connectors during the r&r they more than likely bitched them and the switch.

Line pressure, fuses, I don't know of a way to check to see if the converter got fully seated before trans installation (nothing should have bolted up if it was incorrect)

Next is a scan tool and dvom and check solenoids I think. Though somebody with religious 4l80 experience may have a short answer, like pull it for a SM465 swap

 

[Jrgunn5150]

I would be scrutinizing that PRNDL switch on the side of your trans. If someone tried to disconnect the electrical connectors during the r&r they more than likely bitched them and the switch.

Line pressure, fuses, I don't know of a way to check to see if the converter got fully seated before trans installation (nothing should have bolted up if it was incorrect)

Next is a scan tool and dvom and check solenoids I think. Though somebody with religious 4l80 experience may have a short answer, like pull it for a SM465 swap

That is my first suspect, hopefully they just screwed up the connection.

Fuses are good for the Trans control. If the converter didn't get seated, the pump would have ate itself by now.

I'm really close to pulling the trigger on a Tech 2 clone, I have a buddy with one and he really likes it.

 

[Jrgunn5150]

So, pulled everything apart, blasted it with brake cleaner until my fingers froze, hooked it all back up properly, same thing.

I unhooked the linkage, had my GF start the truck foot on the brake, I manually moved the range selector through the gears, shifter inside indicated P N and that's it.

Looking at the PNP/range switch now I guess.

 

[Jrgunn5150]

I changed the internal wiring harness, along with the EPC solenoid, and all the other solenoids, and the pressure manifold, and the truck is shifting correctly now.

Also, a pan R&R on these takes 7-8 quarts, and the converter doesn't lock until 58 MPH.