Hi all! This is my first post here, mainly because I have always been able to fix any issues with my truck.......until now. This is a 1995 with 210,000 miles on it. There seems to have been a progression to my issues or so I thought.

First Check Engine light came on. I tried the key method to diag. No helpful info there.

Next there was the Check Engine light, tach bouncing, overdrive going in and out. A friend is a Dodge diesel mechanic. He brought home a OBD1 scanner. First attempt to read...no codes. 2nd attempt to read....no codes. Third attempt involved driving with the scanner in cab. The code would come in and then totally clear. It did show a high temp trans code. My friend felt that a bad ground could cause these issues. Looked at some grounds, they looked good. Changed all the cables off both batteries. Double cleaned the grounds on the engine block. Just in case replaced the Trans temp sensor (failed in the past.)

Test drove the truck about 14 miles. No issues. Stopped for about 15 mins. Started to drive home......no tach, no o/d, voltage slowly going south, no air conditioning. More research...Engine speed sensor. Makes perfect sense. Changed the ESS, went for a long drive. After 25 miles I stopped for 10 mins. 24 miles toward home, stopped again.... no issues. The last 500 feet check engine light bouncing , tach bouncing and wait to start and the rest on the t side of dash bouncing on and off. Acts as if there is a power loss then gone.

I do not like changing things without a good understanding of why. Folks here have said the these PCM's are rock solid so I am not looking to replace it yet. Any thoughts anyone has would be so welcome because I am at my wits end. Thanks for your time.

 

How are your batteries? Have you checked them under load?

Sounds like your problem only happens when the truck is warm?

Good luck with this... sounds like a gremlin that will take a while to figure out.

 

OK, you have done well so far, indeed, it appears as if your issue is somewhere in the ESS circuit. Did you inspect the ESS connector while you had it apart for grime, oil, etc? That is one biggie, when you get an oil leak up front, the oil can get into the connector and intermittently short across. If that is good and clean, and the connector pins are in place and not corroded, then you need to start tracing the wiring back, looking for corrosion, or chaffing.

Some more info for you.

 

im gonna second patdaly. sounds like its in the ESS circuit, either the connector or the sensor itself

 

Thank you for your responses. Yes the problem only seems to occur when the truck is warm. I hauled a car trailer unloaded this morning about 12 miles. The truck sat for about an hour in the sun. As soon as I started it up the tach was bouncing, check eng lite on and off, wait to start flashing with the check eng. So it seems to be clearing all codes again. Drove it about 10 miles and it settled down. Makes no sense to me. It was as if the air movement cooled it down and problem went away. Got home, talked with the neighbor a few minutes, stated the truck back up and the tach was at zero and battery voltage going down. I am going to start pulling the wiring harness apart, warm it up and try to induce the issues. The connection for the old and new ESS was good. I had opened it up a few days before and put dielectric grease in it. There is no engine grease around the connection. When I did a search on the forum, someone had a major fuse that was opening up and causing weird stuff. 40 amp. So I think I will change most of the fuses in the dist. box in the engine compartment. That will be after I tear into the wiring. Oh well, at least I will know that much is good after that.