New to me project truck, need help with transmission and other questions

[GrayT]

I just picked up a cool new project truck.

its an 85 chevy square body k20 that has a 1996 5.7 vortec and 4l60e swapped in from a sierra.
It still has its np208 transfer case, but the rest of the drivetrain is stock as far as I know.

Since its not my project its "difficult" to work on, the previous owner had the swap done by a shop but they went out of bushiness and returned it to him non running. I got the engine going and it sounds really good but the trans is in limp mode. It only goes in 3rd gear in drive and will do a 2 3 shift if i move the shifter manually and it has reverse.

I checked the trans fluid, its good. I checked to see if the circle trans connector is getting power on the E pin; its not but the other pink wire pin "N" is getting 12 volts with ignition on. Do these need to be switched?

i have a Bluetooth obd2 reader and while driving it shows a proportionate change in speed from 1 - 2.5 mph. It looks like its using an adapter out of the transfer case to send vss. Could this incorrect speed reading cause limp mode?

The only code the scanner is showing is a rear o2 sensor fault.

Thanks for any help or ideas!

 

[TexasT]

Is it using the "black box" computer? or something else? I would be hunting a trouble shooting tree for that 96 stuff and see where it leads you with the trans not shifting. Look for a 96 service manual, I would think someone has it hosted online somewhere.

 

[Jglew82]

Yes, you need to have ignition power to pin E (key in run AND start positions). If not, then that is most likely your issue. Pin N is in good shape if you have ig power there, that is your manual valve position sensor input from the PCM.

Trace out the wiring, or pull a new wire entirely if the harness is butchered in any way. That wire went to a fuse in the 96 instrument panel fuse block, so it may have been cut back or taped inside the harness somewhere when it was removed.

 

[Greg Gubernath]

Maybe a faulty throttle position sensor 4l60e is computer controlled trans.

 

[GrayT]

thanks for the replies, i added ignition power to pin e and the trans shifted into first. It has a pulse generator on the mechanical speedo that makes 8k pulses so the computer was only reading 1-2 mph and not shifting. I bought a Dakota digital sgi-5e pulse converter and now the trans shifts through every gear.