I have a built trans with a 3000 stall I got everything in and was driving it. Everything was fine then the trans when to shifting in to 4th early so I pulled the DTC and got a P0748 code for the shift solenoid. I also found that the vacuum line had come off not sure how long it has been off. could the vacuum line coming off have caused some damage? I cleared the DTC and it is still shifting early. or am I looking at a wiring issue?

 

Are you using vacuum to control line pressure?

 

I guess so I don't think the trans had the vaccum mod done..

 

You mentioned a vacuum line comming off. What is that for. 748 is a pressure control soleniod code and would just cause firm shifts. Early shifting is a sign of a bad tps signal or Vehicle speed to the controller.

 

oh sorry it is the vaccum line that runs to the 4L65E tans in my car.

 

could the trans desired TQ in the TM screen of the tune being set to 640 cause this?

 

And early shift could be a TPS or MAF calibration error

 

hmm ok I will check them out