Archived Strange electrical problems, 1st gen

[Gardiner]

I have been experiencing random electrical problems lately and need some advice.



At highway speeds the truck sometime drops from 4th down to 3rd gear and then back up to 4th. The 'check engine light' flickers along with 'water in fuel' and the 'brake' light. The voltage guage will normally dip as well. It will also kick the truck out of cruise when this happens. The guage and lights have also flickered off/on at idle once before with a noticable change in engine pitch. This only happens every once in a while and immediately goes away.



In addition the preheated air start up system is currently not working. The thermistor, solenoids and the element have all checked out as good as well as all the associated wiring. These tests were done by Cummins techs, they said it was possible the ECM had a bad ground.



I figured that everything must be related to a bad ECM so I replaced that today with a Mopar unit. No luck, the problem did not go away with the start up element, and I'm assuming that the other problems still exist.



The TPS is less than 1 year old (replaced when the trans was rebuilt), all of the trailer hitch wiring including the controller have been replaced, the alternator has been recently rebuilt, the few accessories I have are running off of relays and the wiring all appears to be fine. The cruise, lights, signals, power locks, stereo etc all work.



I have just basic electrical & mechanical knowledge and don't want to keep spending the $$ having the techs try and trouble shoot the problem. It is just an intermittent problem so it is very difficult to diagnose.



Any suggestions?? It's going back to the shop this Friday. Feedback would be greatly appreciated

 

[Paychk]

Have you checked the grounds near the battery, on the radiator support? There are 3 wires & they are the ground for the engine control module. Also check the battery/engine, engine/firewall grounds. Clean, bright & tight are the rules; take them all apart, wire brush or sand to bare metal, then coat with dielectric compound & tighten. I would also check the Tach sensor; it is mounted on the front of the engine, just above the harmonic balancer. The tach sensor has a plug that is just below the front valve cover and could be corroded.

 

[p-Bar]

Paychk has the right idea, I would think about replacing the batt cables and maybe borrow a VOM volt/ohm/meter from a friend and put it in the circuit to monitor voltage. Are your lights dimming also??

 

[2-ND TIME]

electrical problems

So how is the good city and what part do you live in? Do get a multi meter they are indespensible. The cheaper Flukes are good. Check the fuse links I had to do mine and I put ring connectors in so to make them easier to replace. Could be ignition switch going. Copper cote works better for grounds but use something.

 

[Gardiner]

Thanks guys, I'll take another look at the grounds. They seem fine on the surface, but I'll take a wire brush to them. As far as the tach sensor goes, that appears fine as well.



I don't recall the lights dimming either.



One other thing, the factory stereo doesn't always turn on..... it takes a few off/ons to get it to work. Probably not related, but never hurts to mention it.