2nd Gen Non-Engine/Transmission pcm?

[94ramflatbed]

Hoping to not have to throw parts at my old truck, a 94 3500, thanks in advance for advice/ comments. The charging system has been hit or miss for a while, but a few days ago the speedometer and tachometer quit working. The abs light comes on and goes off like normal, but the wait to start and water in fuel light do not light. It is showing a discharge again as well. I've read the ess can be at fault, but there is no 8v power coming out of the pcm at pin 7 its labeled as a supply in the pinout. and the speedometer quit, thanks to the reading I've been doing I think its on its own circuit. I do have power at the pcm at pins 9 and 3. pins 11 and 12 are grounded. I am showing no voltage at pin 57, the asd relay feed either running or off. Have thought about jumping pin 57 to positive, but don't want to fry anything. I have cleaned the connectors that I can get at and examined for breaks in wiring, any thoughts? Thank you.

 

[B.G. Smith]

I believe the crankshaft position sensor turns on the alternator/tachometer
etc. bg

 

[94ramflatbed]

Thank you BG. It does, but if im reading the schematic the right way, that sensor should be receiving 8 volts power from the ecm. Tested wires for continuity and were okay, just not sending power to the ess. A little under 20000 ohms a across prongs on sensor itself. Isn't lighting cel or any dash lights except abs.

 

[94ramflatbed]

Here's what has me confused, pin 7 says 8v supply. It goes to ess plug and returns to pcm. No power is being applied. Attached a pic I found of the pinout.

 

[94ramflatbed]

Curiosity got the better of me this afternoon and here's what I found. Pcm board leaking oil though a little hole in the protective gell. Tested across the pins for power and ground with an ohm meter, showed dead short. Time to break out the soldering iron. Looking like a blown cap, stinks like bad electronics too, Thanks.

 

[Flinty]

Been following your thread with interest and look forward to seeing of you can get your pcm to start to work again. I put an internal voltage regulator on my alternator like the one Larry b sells. Good job on the trouble shooting.




Link to regulator: http://www.fostertruck.com/alternator-internal-regulator-conversion-kit.html

 

[94ramflatbed]

No dice on the board repair, when I got the gel off it was too far gone, parts of the printed circuit were corroded out. I ended up going to an external voltage regulator.

 

[Missouri Mule]

Glad you found the problem! Your sensors should not receive no more than 5 volts. The signal they send back is varies between 0 to 5 volts depending on the sensor.