6.9 Diesel Glow plug issue

Ford Guy · Jan 3, 2012

I have a 1987 F-250 with a 6.9 Diesel, and the glow plugs cycle, but they only run one cycle, as in they only click once, you have to turn the key on and off to get them to recycle, as they should on their own, and the wait to start light also isnt working. Im thinking that the actual controller, not the relay is bad, i think it is reading that the fuel in the engine is already heated and letting them cycle off, but im not entirely sure, if you have any input it would be greatly appreciated.

stevedrums · Jan 3, 2012

sounds like a controller to me but i am no expert. there is a great diagram floating around this forum that shows you how to wire in a manual switch. just some wire, connectors, fuse and the switch.

sle2115 · Jan 3, 2012

Watch the diagrams for 86 and older as the system is different. If yours is an 87, it should be the solid state system. First thing to do is check the glow plugs. If it short cycles, it's often a plug or more gone south. The ground also is important. Clean the connection on the driver side of the manifold and make sure you have a good ground. Might even want to run a wire to the negative post on the battery (I actually wired one in permanently). The solid state controllers can be wired with a pushbutton, but it is done differently than the older ones. You have to connect a terminal to ground with a switch to switch the gps on.

Wyreth · Jan 3, 2012

The controller only reads block temp, and the resistance of the GP's. Even when mine is warm the WTS light will come on, even if only for a sec, and I get a initial, and afterglow cycle. (briefly)

If the controller clicks, then the relay is likely good. But if you are going to replace the controller, that type comes with a relay in it. (you have the 7.3 system, which is apparently much better)

If they are only clicking once, without afterglow, then it's likely the controller. Or the wiring to it. I'd check the whole system while you're at it.

sle2115 · Jan 3, 2012

Bad glow plugs will short cycle the solid state system as well. It may only be clicking once because it is sensing voltage drop incorrectly (bad glow plugs, bad ground, etc.) I'm not saying it isn't the controller, just saying it might be something else. The solid state controller doesn't sense block temperature like the older system does. It senses the resistance of the glow plugs via voltage drop and burns them accordingly. Mine only shows the wait to start light on the first cycle, not on the afterglow cycle, although you can hear it clicking and see the voltage drop as it cycles.

How old and what type are the glow plugs? Even if new, I'd check them, especially if they are autolites or champion which are known to fail rapidly.

Agnem · Jan 3, 2012

Wyreth said:
The controller only reads block temp, and the resistance of the GP's. Even when mine is warm the WTS light will come on, even if only for a sec, and I get a initial, and afterglow cycle. (briefly)

If the controller clicks, then the relay is likely good. But if you are going to replace the controller, that type comes with a relay in it. (you have the 7.3 system, which is apparently much better)

If they are only clicking once, without afterglow, then it's likely the controller. Or the wiring to it. I'd check the whole system while you're at it.

Be carefull here.... the 87 6.9 is a hybrid that has a lot of the 7.3 improvements. It SHOULD have a 7.3 glow plug controller, and NOT the 6.9 controller, in which case the above comment does not apply, and a manual push button is not recommended. Do a search and consider your engine a 7.3 when it comes to your glow plug system.

Ford Guy · Jan 3, 2012

It has Bosch Glow plugs in it that are probably somewhere about 6 months old, And it does have the solid state 7.3 Glow plug system on it. One thing though, is that i previously had a 7.3 that had bad glow plugs, and even then it would do its normal glow plug cycles, and the light would remain on until it was finished cycling all the way, and then it would struggle to start due to a lack of working glow plugs, This acts like it doesnt want to push the cycles, and after you cycle it over with the key a few times it starts right up as if all of the gps are working, it just isnt cycling correctly, although i will pull the gps out and check continuity on all of them.

6.9 Diesel Glow plug issue

Ford Guy

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stevedrums

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sle2115

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Wyreth

Certifiable Noob

sle2115

NRA LIFE MEMBER

Agnem

Using the Force!

Ford Guy

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