I have a 93 f-350 with a 7.3 idi, I just started having an issue where my glow plugs go on while I’m on the highway on my weekly 45min drive to the state above me, I was wondering if this is a known issue or if it’s due to a problem with my key start, I think it’s the key but I also feel there is a chance of it being the relay where the solid state electronics controlling it could be going bad as well. Has anyone had to deal with this before?

 

sounds like you have multiple issues.
first being the glow plugs should not be working with engine temps over around 120 degrees.

 

Could it have anything to die with the temp gauge not going over an eighth of the way, possibly a bad thermostat

 

not really. the temp gauges on these trucks are not very accurate.
the sender on the driver side of the block is for the gauge, the sender under the alternator next to the thermostat is for the high idle and timing advance.
while a bad t-stat (Stuck open) would usually keep the engine cool, it should still get hotter than 120 degrees. unless of course you are driving in below zero temps.

 

How long have you owned the truck?
Have you ever done anything to the glow plugs or controller since you've owned it?
How do you know the glow plugs are going on ? does the wait to start light illuminate? do you hear them clicking?

Does it just happen once or do they stay on the entire trip?

.

 

Do they come on and do a proper cycle when your going down the road like they would when you start the engine warm? If so, that most likely points to a faulty controller. Mine would do a full cycle going down the road once in a while, then they started cycling a few times over a short drive. My controller is only like 3 years old, so I went to manual gp’s. I thought it was my key switch too, but I would wiggle it when they came on to no avail. I was bouncing in some snow awhile back, and the WTS light blinked a couple times at me but the volt gauge never dropped, showing that something is probly loose in the controller as the light was on but the plugs weren’t.

 

sounds like the Control Unit Temp sensor is Out of Whack.....

This is why most Convert to Manual GP control

 

Thanks for posting that lonewolf. A mechanic at the local dealer printed some pages off for me when I was having issues but they’ve disappeared lol it’s nice to see it all complete there.

There’s been a few times where I’ve really wondered how these parts are handled. I’ve had an oil filter with a small dent in it, an air filter that wasn’t very clean for being new, and my glow plug controller coming in a box that was open. It was probly dropped three times before I got it, but visually it was fine of course. Makes you wonder when it fails in short order.

 

When I Generated it, it was too Large to Post here so I had to Compress it... the Compressed PDF looks OK to me, and should still print fine with a Laser printer it was originally 600 DPI
I thought about putting some stuff up on DropBox but I'm not sure that is the way to go.. I could do Google drive too, but then I'd have to Maintain it LOL

I've Reversed Engineered these controllers years back and repaired a hand full of them... getting the Potting Material out is a PIA but a heat gun sure helps.
I just went with a Stancor Contactor years ago as I always had at least a half dozen in stock for welding equipment. I've never had another issue

Looks like they are getting expensive now as a lot of folks have discovered them

http://www.farnell.com/datasheets/190320.pdf

 

Hey sorry for not replying the other day, I didn’t expect to get this many people replying lol, I have had the truck for maybe 2 months now and have changed 6 of the glow plugs, and plug to do the other two when I do my injectors in a few weeks just to make life easier for the ones under the injector lines, they do a full cycle as if I was doing one trying to start it and I can tell they are on by both a voltage drop and the wait to start light on, if the case is just a bad glow plug controller I have a diagram for making it manual and I will install a button probably this weekend, thanks so much for the help!!!