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Discussion Starter #1
My 90 F250 started having a problem with the glow plugs. I've driven Ford IDI's since 1986 so I'm pretty familiar with all their little problems. But this one has got me stumped. Several weeks ago the wait to start light would only stay on about 2 seconds and then go off and you'd hear the relay clicking real fast. Since the truck is near 25 years old and had it's original glow plug controller, I assumed it had finally bit the dust. I replaced it and the same problem continued. I studied the wiring diagram and the only other thing I could find was the temp sensor attached to the controller, so I replaced that too. Still no change. About all that leaves is the plugs themselves so I had the Ford dealer check them when the truck was in for service. 3 of the 8 tested bad. I've had several bad plug before, but the controller timer would still cycle normally. What have I missed? I'm pretty good at sorting out electrical issues but this one doesn't make sense unless the new controller is bad too.
 

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Perchance that old nemesis, a bad ground?
 

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Check the connectors for damage. This will cause a short cycle time. If they are good, you have a bad plug or two.
 

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Discussion Starter #4
I talked to my local Navistar dealer and they seem to think the bad plugs are the issue. Going to put in a new set and hope that cures it. I have the block heater on a timer so it's easy to crank without them but it sure adds to the electricity bill at the end of the month.
 

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Discussion Starter #6
Jared, so I found out. Replaced them and problem solved. The plug that were in the truck were Motorcraft but they lasted less than a year. I'm trying the Wellman brand this time. They have a good reputation and are made in the USA. I normally have gotten at least 3 years out of a set. Since I suffered a severe physical set back a couple years ago I haven't been able to do much of my own work so I go to the garages. On this work I contacted my local Ford dealer who told me that changing the glow plugs was a 3 hour job which would be $297 labor. I politely told them they were nuts since I had done them many times myself. Checked with the local International dealer and they said about an hour so that's where I took it. They charge exact time on small jobs like that and not what some moron put in a rate book. They charged me 54 minutes which was exactly what it took. I had worked with these guys before and they treat their customers fairly. Even in their waiting area, the canned drink machine prices are 50 cents and most items in the snack machine are the same. Coffee and hot cocoa are free. That's the way customers should be treated at any repair shop.
 

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Discussion Starter #7
Well guys, I spoke too soon. Left the block heater unplugged and when I went to crank it the glow plugs still aren't cycling. Stays on about 3 seconds and then starts clicking fast. I'm going to have the Ford dealer check and make sure they didn't wire the controller wrong. Beginning to sound like a bad ground or the hot and glow plug wires are switched.
 

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I guess that could also be a supply voltage wire or connection or even the switch heating up, increasing resistance causing voltage to go screwy, or similar? That or a ground.
 

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Discussion Starter #9
Jimmie, this thing has gotten even weirder. The original set of glow plugs that failed before I put in the new controller had #1, #7, #8 dead. After I installed a new controller and a complete set of new glow plugs it still didn't work. Took it to the Ford dealer today and they checked it. Guess what? #1, #7, and #8 are dead again. There's no sense in that. It's a 12 volt system and no plug can get more power than the others. Las Vegas wouldn't give odds on something like that happening. I'm about ready to hot wire it and use a push button switch to activate the relay.
 

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I think you can use an external solenoid from a ford tractor starter on those gp's. You might have to gang them for adequate amperage. I imagine that these oem gp controllers could have been built in such a way to save a nickel but they all fry 1,7,& 8. You just got two of them that were made the same way. I have heard folks say that the factory gp controllers for obs fords are crap. Also, since gp's get their ground from the block, the techs need to make sure that the seat is clean.
 

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Has anyone checked the glowplug harness. Possible short to grnd or open can cause this. If you haven't replaced it after that kind of age it would not be a bad idea
 
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