Engine/Transmission (1994 - 1998) Pcm

[shendren]

the trans guys can't find my problem. so they're thinking it may be the pcm. my pcm has the numbers 938 and 56040 on it. i found a used the pcm and it has 983 and 56040 on it. it came out of the same kind of truck as mine. i have the vin #. how can i make sure it is the right one?



thanks. scott.

 

[HoleshotHolset]

put it in and try it... . chances are. . you can't return the used one anyhow... . no matter if you try it or not.



From what I have seen... . it won't smoke and burn up if it's the wrong one.....



Matt

 

[shendren]

tried it. full refund. it didn't work. POS truck.

 

[Cooker]

Scott,



You certinaly have had bad luck lately

 

[Strick-9]

Scott,



Sorry to hear about your repeat trouble. I'm still trying to figure out why someone would throw a governor pressure solenoid at this problem.



Do you have a service manual or wiring diagram for your truck?



Here's two things you can do. Buy a small 12 volt light or LED.



Find a +12V (hot) wire under your dash or run a temporary wire directly from the battery. Hook that wire to the light or to the positive side of the LED. Hook the ground terminal of the light or LED to the lockup wire on your transmission.



In my '98 service manual it shows to be an 18 gauge wire, Orange with a black stripe. Hooked to pin 7 of the transmission solenoid assembly. Yours may be different.



Splice into the harness as close to the transmission as possible.



The light will light up when the transmission gets a signal to lockup much like the dealerships scan tool. But this method will find bad connectors and broken wires as well. The scan tool knows when the PCM is requesting lockup, but this light will illuminate when the transmission is actually receiving the signal to lockup. If the wiring harness is bad, the scan tool won't find it.



Another method would be to install a manual lockup switch. But without knowing where your wiring harness is damaged, that may not work out either. That's why I recommended the light method first.



-Chris

 

[shendren]

so what i really want to see is when the light goes off, i. e. when it goes out of lockup and the rpms go up. right? this bad wire/connector will be hard to find going down the road. ??



thanks alot for the help. scott.

 

[shendren]

i already know when the lockup drops out, due to the rpm going up 50-200rpm. i just need to be able to track the bad wire down. or at least know which sensor is sending the bad signal so i can narrow this down a bit. thanks again for all of the help. scott.