The other day coming home from work in my truck, I looked to see how fast I was going and I saw that my tach was not working and then the alt was not charging and the cruise would not come on and the A/C clutch was not engaged. so I checked all my grounds and cleaned them and all the wire conection and still nothing so I had a friend of mine come over with a scaner and it showed no signal from the tach or the charging system so we thought that with all those things going out all at the same time it was the pcm so I replaced the pcm still no luck it still the same. back to the begining as I was driving down the road I hit a bump in the road and it all was working till I got home and when I went to move the truck it wasn't working agine. so any thoughts or has any body ran in to this problem

also I looked at all the other threads
the truck is a 97 2500 4X4 diesel

 

Crank sensor or the wiring is bad. Check the wiring first, also make sure the sensor didn't come loose and fall off.

 

What he said! The PCM doesn't know the engine is running, so it doesn't turn all that stuff on.

 

i have a 97' diesel with same problems I also was told to replace ecm and did with same problems it will come on sometimes(ac, tach, alternator) but it still has trouble shifting into overdrive- it will rev up to 60 mph then i have to back out if it for it to go into overdrive. I also checked speed sensor the book says it operates all of these to but it was not it. i was also told to check crank shaft sensor but have not yet... I really hope this is it i spent $700 on an ecm. Good Luck and i will get back with you if find this sensor works..

 

You don't have an ECM, you have a PCM. The intermittant failure could very possibly be just a bad ground from the rpm sensor. Did you keep your old PCM?

 

yeah your right don't know why i typed ecm- two other people said it could be the crank shaft sensor or bad wiring- is that what you were refering to when you said the ground to rpm. yes i have old computer.

 

i thought that the truck woldn't run at all if it was a bad crank sensor. i'm having the same sort of problems in my dizzle and was told about fusable link wires. aparently they run off the poast clamps off the battery. i changed out the wires and put in new ones along with a fusable link there were two on one battery both on the positive side and one on the neg on the other battery. one of the wires goes to the fuse box under the hood to the alt relay. just curious, but u checked that it was ok? let me know what u came up with b/c i havn't had the best of luck

 

A 12 valve will run with no electrical system at all if you tie up the shutoff solenoid. All the crank sensor does is tell the PCM what the RPM is. If RPM = 0, then the PCM figures the engine isn't running so it won't turn on any of the stuff it runs.

 

I purchased my 93 cummins 5yrs ago, havent had a problem with it till now.
couple of weeks ago the alternator wasnt charging my a/c compressor shut down and the tranny wasnt shifting right and to top it off I couldnt keep it running at a stop light without reving the engine up.
So I had a friend who is a diesel mech. he said it was the alt so he changed it it did the same thing put another one on worked perfect for 55 miles lost charge ac quit and the truck died.
I went to Dodge dealer he said it was the PCM.
Now I dont know which way to go.
Is it the crank sensor or the PCM.
What voltage or what OHMS should you have on the crankshaft sensor.
Unfortunatly it is erratic some days it works perfect and some days it doesnt work at all.
Any help would be greatfull.

 

Crank sensor is cheaper. Usually it's the wiring or the connector, though. Take a good look at the wiring, especially where it comes around the front of the head.

 

should be 5 volts at the sensor