6.9 Glow plug issue.

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Nov 1, 2020 | 12:00 PM

ragboat

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6.9 Glow plug issue.

1987 F250 with the 6.9 Diesel. It seems like my glow controller is not working. The 'Wait" light only flashes for a moment and there is only a momentary voltage drop. I'm used to seeing about 10-15 seconds of light and voltage drop. Troubleshooting it has me thinking that the latching relay has failed. That can't be purchased separately. I am considering wiring the system for manual control. The Ford manual cautions against that because they use 6 volt plugs and cycle them for fast heating. Has anyone wired for manual control? I'm the only driver so I can limit the heating time to the 10 of 15 seconds I'm used to. I would use the existing power relay but wire it to a push button switch. Any ideas or cautions?

Nov 1, 2020 | 08:16 PM

ragboat

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I got it converted to manual glow plug control. I disconnected the red and white wires from the controller leaving the red/light green attached. This allowed the relay to get control voltage. The white wire is supposed to take current through the timing circuitry to ground. This is where the failure had occurred. I wired in a push button switch between this post and ground eliminating the failed timer. I now just have to do a short count when I push the button. I even get the wait light telling me that voltage is being applied to the glow plugs.

Nov 2, 2020 | 04:06 AM

84_6.9

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I did the manual conversion on my 84 6.9. I would caution you to hit the switch for no more than six seconds, let off for two or three, hit again, and cycle as needed. As long as you’re running Zd1 plugs anyways. If you convert the system to the zd9 you won’t need to cycle.

Also, make sure you’re running motorcraft plugs. It’s a MUST. There’s quite a few threads on that.

Nov 2, 2020 | 04:32 AM

ragboat

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Thanks for that advice. What is the difference between the ZD1 and the ZD9 plug?

Nov 2, 2020 | 06:03 AM

84_6.9

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Quote:

Originally Posted by ragboat

Thanks for that advice. What is the difference between the ZD1 and the ZD9 plug?

The zd1 is a 6 volt plug. If you run it for more than 8 seconds or so at a time, it’s prone to burning out. The zd9 was the plug used on the 7.3 idi, and it’s able to withstand longer cycle times.

Also, the plug on the zd1 is a spade connector, the zd9 is a bullet connector. That’s how you tell which one is which. If you buy anything besides a motorcraft plug, you run the risk of the plug swelling inside the head. Then you’ve gotta pull the head to get the plug out. Not exactly my idea of a good time.

Nov 2, 2020 | 06:42 AM

tjc transport

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what he said. with ZD-1 plugs on a manual switch, you only want to power the plugs for 6-8 seconds.
ZD-9 plugs get 15 seconds glow time.
since your truck is an 87, you will have to see what plugs are in it. 87 used both the old style controller, and midyear switched to the new 7.3 solid state controller.