Hello,

Long time lurker, first time poster. I have a problem that I think has to do with the ESS like others, but can't seem to keep fixed.

On my 1994 Ram 2500 5.9l diesel, the symptoms were that the tachometer started bouncing around then fell and stayed at 0 rpms, the air conditioner quit, the truck wouldn't enter overdrive, and the alternator stopped charging the batteries (my voltmeter dropped from 14 to 12 when running).

A mechanic I talked to thought that the alternator died. After reading on various forums I thought that I might have a faulty voltage regulator inside the Powertrain Control Module (PCM) (which I read could be fixed with an external voltage regulator). Then I did some more reading and all signs pointed to the Engine Speed Sensor (ESS) sometimes incorrectly called the Crankshaft Position Sensor (CPS). If the ESS doesn't tell the PCM that the engine is running, then the PCM won't allow 4th gear, A/C, alternator charging of the batteries, and can't tell what the RPMs are at.

I was pretty sure I was going to have to buy a new ESS for $60 to $100 (beats buying a PCM), but I wanted to check to make sure mine was bad. After testing at the connector, it seemed that the ESS was getting its required 8V input (with the truck on but not running) and the ground looked good. So I pulled out the ESS itself and measured its sensing abilities (again truck on, not running) by touching and pulling away a hunk of steel. It did change voltage readings at the sending wire from 3mV (or was it 30mV?) when touching the steel to 5V without the steel. So since everything seemed fine I regapped the sensor with a piece of a CD (0.047 inches - gap is supposed to be 0.05) and started the truck up. Still the same problems.

I had noticed that the connector was loose-fitting and the previous owner had zip-tied it together, so I jiggled it around and got everything fixed for a short drive, but after going over a bump the same problems reoccurred. After trying to stuff copper wire in the sockets to shore up the connection unsuccessfully, I cut off the connector from both sides and re-connected the 3 wires with spade connectors. It was hard to figure which wire went to which wire, but I figured it out by opening the connectors. Problem fixed for a day.

The next day (today) my fiancee started up the truck and informed me that my fix did not take. I'm at my wit's end now, since the ESS seems fine and all of the signals in every direction seem fine. The only thing I can think of is an intermittent ground fault that only occurs when my fiancee starts up the truck. Any suggestions?

 

I have a similar problem....and Im sure its my pcm. I did the external regulator to keep driving, but my gauges are out, the ac, the cruise functions etc....My 5 inch down pipe came off, and I cooked the pcm....about 8 inches away. Im in search of a 98 12 v manual pcm.....its not going well....so far. Even places that say they have it, come back and say sorry.

 

1320, hit up member Redlinear yet?

He probably has one kicking around somewhere.

 

A while ago there were several PCMs for our trucks for sale on a certain popular internet bidding website. They still have ones for '94 '95 and '96. Also, I think my truck is still able to enter overdrive; if I hit the "disable overdrive" button when going above 55 mph, the truck drops into a lower gear. Anyone have any ideas?