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4l80e shift problem

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Location
Swanzey,nh
Thread starter #1
I swapped a 1999 4l80e into my 1995 k3500, it was a 4l80e to 4l80e swap. Since the swap the transmission won't shift out of 2nd gear under hard acceleration, and the only way to get it to shift again is to stop and shut the truck off. If I roll through the throttle slowly it shifts fine. Is there anyway to correct this issue?

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Messages
6
Likes
4
Location
Swanzey,nh
Thread starter #3
Any codes?
It is going into limp mode to protect itself and still allow movement off the road. Cutting power via key off resets it.
No codes at all. Once it's put of 2nd gear everything is normal, it will kick down, shift up again like normal. I thought it might be a difference in speed sensors but they are the same for a 1995 and 1999

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THEFERMANATOR

FRANKENBURBAN
Staff member
Lead Moderator
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Staff #6
They list a mid year change in converters for 97, but this doesn't sound like that. There was an issue with early trucks hanging in 2nd, and it requiref an updated prom chip to correct. I had to do it to my 95 because it would hang in 2nd, but it never stayed in 2nd, it would always eventually shift. Sticking in 2nd gear is limp mode. The thi,g about limp mode is the codes can clear by turning the key off.

When you say it sticks in wnd under hard accel, if you come to a stop and take off again after it doesthis, does it stay in wnd still, or will it go back to 1st? Trying to understand exactly whats going on. Which converter did you use? If you use say a 6.0l converter, your slippage could be so high in 2nd, it's not going to shift. The 6.5l is set up to shift by speed, not rpm, so if your converter is stalling to high, you may not reach the 2-3 shift speed before it pegs out on the governor. You could also have a valve hanging in the valve body when line pressure goes up. In a situation like this I like to start by connecting a scanner and seeing if it is actually commanding the shift to occur. Thisway you know if you needto look at an electrical issue, or hydraulic.
 
Messages
6
Likes
4
Location
Swanzey,nh
Thread starter #7
They list a mid year change in converters for 97, but this doesn't sound like that. There was an issue with early trucks hanging in 2nd, and it requiref an updated prom chip to correct. I had to do it to my 95 because it would hang in 2nd, but it never stayed in 2nd, it would always eventually shift. Sticking in 2nd gear is limp mode. The thi,g about limp mode is the codes can clear by turning the key off.

When you say it sticks in wnd under hard accel, if you come to a stop and take off again after it doesthis, does it stay in wnd still, or will it go back to 1st? Trying to understand exactly whats going on. Which converter did you use? If you use say a 6.0l converter, your slippage could be so high in 2nd, it's not going to shift. The 6.5l is set up to shift by speed, not rpm, so if your converter is stalling to high, you may not reach the 2-3 shift speed before it pegs out on the governor. You could also have a valve hanging in the valve body when line pressure goes up. In a situation like this I like to start by connecting a scanner and seeing if it is actually commanding the shift to occur. Thisway you know if you needto look at an electrical issue, or hydraulic.
I used my original 1995 converter, my truck has the 7.4 in it. If I don't shut the truck completely off the truck won't come out of 2nd. Not sure if it helps or gives any clues but I can manually shift it under hard acceleration and it shifts fine.

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THEFERMANATOR

FRANKENBURBAN
Staff member
Lead Moderator
Messages
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Location
ZEPHYRHILLS FL
Staff #8
You need to get a scanner on it. Stuck in 2nd is limp mode, and should definately code. Manually shifting it should make no difference as it is still shifted electronically. Have you tried it in 3rd and see if it shifts correctly? You may be getting some cross leakage at the seals for the psm, and it may not be reading the selected gear correctly. All of this is guessing though without seeing a data stream of what it is doing.
 
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