New glo plugs, started fine for a week, now won't fire.

[hallgren87idi]

So I have been absent here for awhile, mainly due to my truck not giving me any issues, but that has changed as of recently. 1987 F250 6.9, auto FWIW, I had an issue with it not starting, so I replaced all 8 glow plugs with the motorcraft zd9's, truck started better than it ever had, for about a week. So what happens now is, I turn the key on, let the glow plugs cycle, light goes off, with no clicking sounds anymore, as I had before I replaced the glow plugs, but it won't fire without ether. May this be an issue with the relay? I will do some searching about how to test a glo plug relay, but I figured I would explain my situation here first. Thanks.

 

[BrianX128]

Try to take a wire to a glow plug off, plug a test light or any light bulb you have into it and when you turn the key to on peek out under the hood and see if that light turns on. It should turn on for some amount of time even though the draw for the system won't be the same. If you get nothing at all then you can trace the problem the other way.

Like this from when I first got the truck..

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[pelky350]

Sounds like relay or controller isue, relays are relitivly cheapif I recall and easy to change if you don't have a turbo wouldn't hurt to change it if it's old anyway, if that doesn't work then it's wiring or controller

 

[chillman88]

Like Brian said, make sure you're getting power to the plugs.

I changed all mine out and put in 4ga wire to replace the bad factory wires. Worked great until it wouldn't start one day, same symptoms as yours. Turns out I had blown the 150amp fuse I used. Put in a 200amp and all's well now.

 

[icanfixall]

If you installed motorcraft beru zd 9 plugs you have the solid state controller.
on the passenger side of the engine is the engine main wire harness plug. One end of this has 2 yellow wires that feeds power to the controller. That plug is too small and any corrosion creates heat that ends up starting a electrical fire. Mine smoked one morning startup. I thought I burned up the starter but nope. Felt the plug and it broke in my hand. was hot as hell too.. Plenty of posts about running a bypass power cable directly to the controller. BTW this feed wire is positive and hot no matter what the ignition key is placed at. So is the alternator heavy power wire.

 

[hallgren87idi]

Thanks for the suggestions guys, going to actually go dig into it a bit deeper today, I bought a new volt meter so I can properly diagnose this hopefully...I believe the controller is fine, the wts light comes on for about 10 seconds then goes off, but we'll see.

 

[hallgren87idi]

Update: Pretty sure the glow plug relay is fried, it's not sending any juice to the glow plug wires. I'm going to dig through these forums and find out how to wire them through a ford starter solenoid, and just run a momentary push button switch like used for starters.

 

[madpogue]

A Ford starter RELAY (the solenoid is part of the starter) will NOT suffice to run the glow plugs. The glow plugs take a LOT more current, and may run for longer on-time, than the starter. Get a Stancor 586-902 or Western Plow 56131K; they're rated for continuous on-time duty and plenty of current for the GPs.

 

[snicklas]

Or, the replacement contactor for the 7.3 system is an Echlin GPR109 from NAPA. It bolts directly in place on the factory 7.3 controller.

 

[red41neck]

I had same type of problem, weak battery connections. Sounds dumm, but cleaned both battery terminals and charged the batteries.
Weak battery and or dirty connection with still turn engine over but not enought to start.