12 Valve Problem! CEL no TACh

cumminsbus

cumminsbus

Reconstruction Era
Joined
Mar 2, 2008
Messages
661
Recently bought a 12 valve and I am new to the motors.

The Truck:

1996 3500 4x4 auto with 168k miles


PROBLEM
In the mornings when I get in the truck the water in fuel light, wait to start, and trans temp light along with the check engine light stay on and never turn off. I then start the truck and the lights stay on.The tach along the speedometer do not work. When I try to drive the truck feels like it has no power and it stays stuck in 2nd or 3rd gear. After driving for a few minutes the lights will shut off and the Tach and speedometer begin working.

The Volt meter reads about 9 volts while the truck is acting up and then will go back to normal operating voltage.

I had the batteries tested at autozone and they said they were still good. I went ahead and replaced the alternator.

Any Ideas?
 
Alternator will not charge unless the PCM is receiving a tachometer signal.. voltage regulator is in the PCM. Sounds like a bad PCM to me.. The no power thing sounds like a stock 12 valve to me. LOL Take off the AFC and slide the stock plate forward and take some tension off of the AFC spring. Check all connections before replacing the PCM, but that's what I've seen cause the same problems you are having..
 
Next time it does it wiggle the wires that plug into the computer I had a freinds truck that was doing similar things turns out it was in the computer.
 
XTrEmE9156 said:
Alternator will not charge unless the PCM is receiving a tachometer signal.. voltage regulator is in the PCM. Sounds like a bad PCM to me.. The no power thing sounds like a stock 12 valve to me. LOL Take off the AFC and slide the stock plate forward and take some tension off of the AFC spring. Check all connections before replacing the PCM, but that's what I've seen cause the same problems you are having..
Click to expand...

TRuck has decent power when it is runnning right. It has a moded pump with a 4k kit gov springs etc
 
As soon as the truck warms up to about 160 degrees everything starts working great.

I am lost as to what may be wrong
 
Next time you start out hook a bunjee cord up up to the fuel shut off to keep it up (remember it wont shut off when this is done) then if the power is back its just the drop in voltage causing the lack of power . If you have changed out the crank sensor check under the batteries there is a sensor under one or both of them if the computer is told by one of them that the battery is frozen it will not charge until it warms up. Rich
 
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