mrb04

The truck has always had this problem with trans and has had differant tunes with the same issue. I am pretty sure it is something easy I just thought I would ask for some ideas. Basicly what it does is if you take off and drive the truck for sometimes 5 minutes, sometimes 20, sometimes it never does it at say 60 then when you go to take off again 1rst to 2nd shift like it is under wot when you just barly take off. And will continue to do this until you cycle ignition you can turn it off and start it right back up and it will be fine. Truck has a Rpm built level 5 4l70e trans that feels really good and a Precision Industries 2400 stall. thanks in advance

95 bright teal

"when you go to take off again 1rst to 2nd shift like it is under wot when you just barly take off. And will continue to do this until you cycle ignition you can turn it off and start it right back up and it will be fine."

can you rephrase that im lost? not sure what its doing

kbracing96

iTrader: (26)

Sounds like something is throwing a code and putting it into limp mode and commanding full line pressure. Cycling the key reset the code.

FLT

iTrader: (1)

You are 110% correct. Scan the vehicle for codes. Vince

mrb04

even when no light or message goes on?

00ChevyScott

iTrader: (10)

yep, just because the light isnt on doesnt mean there are no codes.

mrb04

I do get a code po108 for map high voltage. would that cause trans to go to limp mode? I am thinking it would due to it determines wot. I ideas on whats wrong trucks has a radix and gm intake. thanks

FLT

iTrader: (1)

I believe that the code is making the transmission go to max line pressure. This is why it is hard shifting. I would address that code and more than likely your problem will be solved. Vince

ForcedTQ

iTrader: (1)

What Vince said, the trans tables reference the Vacuum/Boost signal from the MAP sensor to determine the load on the drivetrain. They then adjust the apply pressures that the solenoids actuate at to engage the various bands and clutch packs. This is the equivalent of having a vacuum signal problem on a vacuum modulated transmission. The computers on these transmissions are very dependent on the accuracy of the information sent by the engines sensors.