Engine/Transmission (1994 - 1998) Electrical problem

[KMacnicol]

Its a '94 3500. The tach, alternator, O. D. , a/c and cruise all quit working at the same time. I replaced the ignition switch and it started working again for 2 days. I was driving the truck today and hit a bump and it all went out again. It acts like the switch is in the on position but the truck is not running (even though it is). Any help would be greatly appreciated. Thanks,Kevin

 

[Joe G.]

It sounds like you have a short that blows fuse #9.

 

[KMacnicol]

No blown fuses. I turned the key to the on position and the air heater relays were clicking and the tach was jumping around (engine not running) and I started checking connections at the PCM and it stopped. I dont know if it was a coincidence or not. I cleaned the connection at the PCM. Still not working. Bad PCM?

 

[tp0d]

What did you clean the connections with? I highly recommend the TV tuner cleaner+lube from Radioshack.

You also want to run down all the ground connections you can find and take them off, scrape the heck out of both sides of the joint (bare metal), relube, and reassemble. I bet thats where the problem lies.

There also have been issues with broken wires due to using the tilt wheel over time. Those are a bugger to hunt down.

good luck

-j

 

[K5IP]

Probably not much help here, but If you start tracking things down in order, start with the tach. Loss of the engine speed sensor output (tach signal) will cause the pcm to think the engine is not running and that will cause most of your other faults. As long as you are cleaning connectors, do the one for the speed sensor located just above the device itself. It is subject to dirt/water because it is directly behind the fan.

Rog

 

[LandShark]

What codes can you pull? Have you checked the PCM for the +5 volts that supplies various sensors? Anything wierd happening with the 'Wait to Start' light?

A bad engine speed sensor can cause all your problems, but so can a bad connection, ground, or PCM.

 

[Vaughn MacKenzie]

I had a similar problem with my '96 and ended up having to replace the PCM. There are used ones kicking around out there if you call a wrecking yard & have them do a search.

 

[KMacnicol]

I think/hope I have it narrowed down to the PCM. If I let it cool down everything will work except alt. voltage is erratic. If I mess with the connection at the PCM while its working it will malfunction. After about 3-5min. of running it will quit working completely even if I move the connector around. Let it cool down for about an hour and it will do the same thing over again.



One problem I am having is the truck had a TSB done on it in '95 and the pt. # on the PCM doesnt match any of the ones I have found (rebuilt or used). Not sure what I should order. The number on the one I have is 4798745. All the ones I found are 8 digit numbers and start with a 5. Thanks again for the replies.

 

[LandShark]

Good luck finding the right part number. Even Dodge took an hour to figure out what to order when I replaced my PCM last year. My old PCM had Part# 56028335 which didn't match Dodge's numbers (I bought the truck new). Possible #'s for a 94-95 with auto should be 56028334, 56027304, or 56028336.

I found that all internet companies that show prices for these PCM's didn't have any in stock, so I ordered from a Dodge dealer.

 

[K5IP]

Let us know what solves it.

Rog