1998 24valve 2500 4X4. About two months ago I was driving down the road and my tach started to read erratic. Finally, the tach read zero, my volt gauge dropped, and I lost some power. All of a sudden the tach bounced back up again and everything was fine. Well, on my way home from vacation and towing my boat it started to do it again. I made it home and immediately figured it was the alt. I bought one from my nearest dealer and installed it this morning. Still, no tach and no charging. I am new to working on this thing and figured the voltage regulator was built into the alt. Wrong, again!!! Could I be dealing with a faulty PCM? Or is there somewhere else I should be looking? Any help would be much appreciated.

 

Check the crank position sensor and its wiring. If the PCM doesn't get a signal from the CPS it thinks the engine isn't running, so no charging system or A/C. The CPS is located just above the damper on the front of the engine. The wiring often gets chafed or broken due to heat. Check the gap as well, a folded matchbook cover is about right for the .050 clearance. The clearance must be set with a non-magnetic feeler.

 

Correct me if I am wrong here (which is often), if there is a failure with the crank position sensor wouldn't the truck not start or run at all?

 

I helped a buddy does his KDP. When reinstalling the CPS there was a little to much force used, which in turn broke the sensor. He drove around for two days on just batteries before being left on the side of the road.

 

The truck is a 12 valve. The crank sensor only lets the PCM know the engine is running and supplies info for the tach. 24 valve is a different animal.

 

The same thing happened to my 95 12 valve.I tryed verything the good people on diesel truck forums told me to do . It ended up being the PCM. Theres some good people out there.

 

I'm sorry to hijack this thread, but I'm having similar problems, and this problem has to get fixed. See thread 1 and thread 2.

Thanks.