PCM isnt commanding 1st Gear on 4L60e

[usar17]

Ok, Frankenstein truck here. 85 body and frame but...
1991 TBI 350 Engine
1991 K5 instrument cluster
1994 4L60e Transmission
1991 NP241c
1994 Wiring harness, VSSB, PCM

I have tried 2 different PCMs and 2 VSSBs, but the truck starts in 2nd gear. I haven't gone fast enough to see if 4th works yet. Speedo doesn't move till around 30 MPH, but the ALDL data shows accurate speed to PCM. ALDL datastream is showing proper column shift position, and proper function of Solenoid B for 2-3 shift. OHMs test of Solenoid A is good, 12v test I can hear solenoid activating. All wiring is good, no shorts that I can find. With transmission harness unplug the ALDL data is still showing the PCM commanding 2nd gear from the start. This is a frame up build so all parts are new to me. Just ordered a new a new Speed sensor from Rockauto today to try that. Wont activate Solenoid A even with shifter in 1st. So something is making these PCMs think it 2nd gear is needed. thoughts, im losing my mind here

 

[yevgenievich]

Might be internal. I had similar issue with 4l60e that turned out to be a seal blown internally. Computer would never show comanding 1st or 2nd and would ignore manual command. Always started out in 3rd, 4th and OD worked just fine. Sure way to check would be manually give signal to correct solenoids and place shifter in 1st. In my case the trans just bogged down and would not move indicating cross leak.

 

[usar17]

I just replaced the solenoids and internal wiring today. Noticed the 3-2 solenoid connector was broke off. Gonna fill it back up tomorrow morning and test it. If that or the new speed sensor doesnt fix things im taking it to a trans shop :/

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[usar17]

And sucks bc i just rebuilt the transmission before putting it in. All new seals, clutches, steels, filters. Only things i didnt replace were the solenoids

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[usar17]

Dropped the pan today. Seems solenoid a was clogged by its own screen. Replaced the solenoid and everythings working properly now. That explains why i heard the vavle clicking still. Its amazing that these PCMs can realize and issue and maintain functions around it.

But 1 other problem still continues. My speedometer I'd way off. But oddly the PCM's data stream has a dead on vehicle speed when compared to my phones gps speedo app. Why would there be 2 different readings? 1991 speedo with 94 drac?

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[foamypirate]

Does the 94 use a VSSB instead of a DRAC? That might be it, if so. Glad you got the trans piece figured out!

 

[usar17]

Yes. 94 is the VSSB using 2 banks of jumpers. I havent been able to find any data tho that they transmit different pulses to the speedo. The VSSB extra bank is for transmission control. Ive read a vssb can replace a drac but a drac cant replace a vssb bc of the needed jumpers for the 4l60e. So they should produce the same pulses. Ill check my grounds. What does the speedo take 5, 10 or 12v?

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[usar17]

Think i found the issue.... printed circuit is F'd. The ground was broke off in the grey clip that goes to the speedo. Pulled the grey clip off and the 12v and signal dont look much better. Can i even get a new printed circuit for a 91? LMC doesnt even list them

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[foamypirate]

Think i found the issue.... printed circuit is F'd. The ground was broke off in the grey clip that goes to the speedo. Pulled the grey clip off and the 12v and signal dont look much better. Can i even get a new printed circuit for a 91? LMC doesnt even list them

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

Might be worth checking ClassicParts or Brothers Truck Parts.

 

[usar17]

Ill look. May try and use gator clips to jump this for time being....middle ground copper broke trying to fix it.

You must be registered for see images attach

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[usar17]

Nothing on classic parts. Brothers has lenses but no circuits. Damn. I dont need to buy a whole new $150 cluster from ebay

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[Georgeb]

It looks like it got hot.

 

[usar17]

Thats the flash from the photo. It isnt burnt. Corroded some, but mainly it the circuit sheet separated

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208