I'm not sure where to start....my 88 F250 7.3 shows a discharge on voltmeter. Should read 13.5 volts but shows to be around 12.5 volts. Periodically it will cycle and the wait to start light will come on. Almost like it cycles after you start it until cyclinders get warm. Only it will cycle after warm or whenever. All glow plugs are good now, found one bad one and have replaced it. Can someone please give some ideas of what could be the problem....tku.

 

I think your voltage regulator is busted. You can get them cheap anywhere. $10.

how old is your alternator? How old are your batteries? Could be that as well, but start with your VR.

 

It could also be a problem with your glow plug controller. It should not cycle after the engine is warm. Disconnect it after the engine is running and watch the voltmeter. If voltage goes up to 13.5 then you may want to look for problems with the glow plug controller.

 

Where is voltage regulator and what does it look like? How can it be tested? Alternator never been changed. Batteries both brand new....

 

if you have an 88, it's on the side wall of the engine compartment of your truck. it looks like this:

 

I don't know. But if you buy one cheap from an online place, you can pick them up for $6. probably not even worth testing. From what I've experienced and read, these things go haywire sporadically, so it's hard to tell if they are good or bad. Kind of like how your gauge is acting.

BTW, did you have any other weird electronic issues? Like did you have some aftermarket stuff (like a radio or digital temp gauge) act weird? Or is your fuel gauge showing weird results too? If yes, then your voltage regulator is allowing the alternator to over charge or under charge, which messes up pretty much anything other than a light bulb. You'll replace this VR and it should fix a lot of weird things.

Also, If your VR is bad, you might want to considering doing an Alternator rebuild. (or do the infamous 3G swap-out, which removed the external regulator from the whole truck anyway, but that's a different thread). The reason why you should rebuild your alternator, is because if your VR was bad, it might have allowed the alternator to run non-stop for a long time. that's some decent wear and tear on these alternators, and if your alternator is original with the truck, it might be due anyway. A reasonable alternator shop should be able to rebuild it for $75 or less.

 

Perk85, which wires do you unhook to disconnect theglow plug relay?...Genscripter I know right where it is.....never knew what it was though. Can it be tested?

 

Genscripter, no other electrical issues other than what I have shared..

 

I have the old style glow plug controller 6.9L with the relay mounted on the passenger side fender. Yours should be mounted on the engine, electronic controller and relay together as an assembly. The relay should have two large terminals with 5/16 studs and one small terminal. Disconnect the small wire. It may have a single wire connector to the electronic module. It has been too long since I've seen one. I have to agree with others here that say the voltage regulator may be bad. You will have to eliminate one thing at a time.

 

Genscripter and perk85f250 wanted today thank both of you for your time in helping me with my problem. Replaced voltage regulator today.. fixed my problem. Voltmeter now reads 13.5 volts like it should. Appreciate it!

 

Glad to help. I had the same problem when I bought my IDI. But my stock volt gauge wasn't working, so it was a lot harder to diagnose.

 

I installed a voltmeter a few years back. You can't rely on the factory ammeter and I also keep a spare voltage regulator around the house or in the truck. Good to hear that you fixed it!

 

This was a quick and easy temporary solution: