Hi Guys,

I'd read, searched, and reread posts on here, thought I had it all figured out in my mind as to what I had and how to diagnose it etc.

I have an 89 F350 with the 7.3L, as far as I know everything is stock. (I'm the second owner.) I've had the truck about 6 years, works well, good strong truck. On occasion, the glow plug circuit won't cycle when I go to start the truck. It's became more frequent this winter, so I thought I'd start chasing it down to fix it.

After searching/reading on here, I figured that my system would have the two relays, one on the inner fender, and one on the back of the block. So, armed with this the other day, when it wouldn't cycle the plugs, I popped the hood, and surprise!!, no relay on the inner fender, instead there's a little (maybe 3x3") silver box instead. Being determined, I thought I'd at least see what I could do at the glow plug relay, so I jumped the relay to activate the glow plugs....waited about 6-8 seconds, then hopped back in the truck to see if it would start....fired a couple times and died, so I then turned the key off and back on....and voila, the glow plugs started to cycle on and off.

To sum it up, I've figured that I have the system with the 'box' controller on the fender, and that it must be dieing a slow death. It seems to work about 50% of the time, as long as the plugs cycle, the truck starts great. I haven't priced out a new controller yet, but also don't have a problem with going to a manual system if I can do so easily, but darned if I can find the thread I read the other day about that swap on this system.

Can someone help me out, and either point me to the appropriate threads, or fill me in on my options and how to go about this?

Thanks!!

Mark

 

check all the connections first. it sounds like you have something as simple as a loose or dirty connection.

 

I've cleaned the connections at the glow plug relay (on the motor), the silver box has a plug in type connection, is that the one you're suggesting I clean? On this system, where is the temperature sensor for the GP circuit, maybe there's a connection there that needs cleaned?

Thanks again,
Mark

 

There is no physical sensor the controller reads the heat by the GP ohms resistance and voltages.

Sent you an email.........

 

silver box on the fender is the voltage regulator for the alt it does nothing for the glow plugs.
follow the positive battery cables from the passenger battery
the large one goes down to the starter, follow the smaller one to the fender, it should land on a relay, on this relay there should be 2, 10 gauge yellow wires that feed the glowplugsnd , check and clean connections if needed, keep following yellow wires to a plug thats between the fender and engine, pull the plug apart and check it real good its well known for melting

 

Glow plug relay and controller on an 87 and later model truck.
Mounted on the intake manifold behind the air cleaner and next to the fire wall.
The cover is removed in the picture.



Relay on top, controller is under the relay.

CAUTION, the battery terminal has battery voltage at all times if the batteries are hooked up.
The ignition terminal should have voltage on it when the key is in the ON position.
COMMON PROBLEM The ground wire must have a good ground, it is normally attached under one of the two mounting bolts.

 

Ok...at one point I thought the relay on the fender was part of the system, but when I jumped the main terminals the starter rolled over....which I wasn't expecting. Since I had recently replaced the starter and knew there is a solenoid directly on it. (And yes, I learned about that %$#* top bolt on here, though for some reason I didn't realize it was slightly smaller in size than the other two bolts!!!)

Hopefully (weather pending, we have a winter storm warning in effect tonight/tomorrow) I will get a chance to do some more testing, cleaning of terminals etc. tomorrow. (Outdoor workshops are great in the right type of weather, but the rest of the time they suck.)

Mark