GP's stay energized - Diesel Forum - TheDieselStop.com
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post #1 of 6 (permalink) Old 08-16-2019, 02:06 PM Thread Starter
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GP's stay energized

Hey everyone, I have an '88 f250 zf5. My GP's were not firing and I've been troubleshooting. I jumped the large terminals on GP relay for 8 seconds then jumped in the truck and it started right up. I then pulled the relay and ground from controller. Gave everything a good cleaning and hooked back up. Now when I turn the key volt meter in dash sits at 9v and won't come back up. Truck fires right up but GP's stay energized. I shut the truck down when I noticed smoke coming from fusible links on fender relay. Did I miss something when I hooked the relay back up? I don't want to cook my plugs

'88 f-250 NA zf5 4x4 208k miles
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post #2 of 6 (permalink) Old 08-18-2019, 08:46 AM
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My guess is that you reconnected the wires incorrectly OR the relay is stuck on. I would be more concerned about cooking your wiring which on an old truck is difficult to source. Under 12v a glow plug will never melt. I once tried to destroy some glow plugs (bench testing) and at nearly 18 volts for more than an hour... they just sat there and glowed. Hind-sight is 20/20 and so is a picture. When you are making repairs like this, use that smartphone and take a few pictures for reference.


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post #3 of 6 (permalink) Old 08-18-2019, 01:04 PM
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^^^^What he said

1993 F-350 crew cab non-turbo 5 speed transmission
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post #4 of 6 (permalink) Old 08-18-2019, 02:02 PM
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Maybe someone has a wiring diagram for an '88 or a picture of theirs to share...


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post #5 of 6 (permalink) Old 08-18-2019, 06:30 PM Thread Starter
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I found a picture and things look like they are hooked up properly. The relay seems to work. Volt meter shows 12.7 at battery side of relay. 10 on GP side when ignition wire is energized. Sounds normal. Battery side voltage drops to 9 and steadily climbs to 10.5 when relay is engaged. are the fusible links preventing enough amps from flowing to the plugs to cause slow heat of plugs and thus a long cycle?

'88 f-250 NA zf5 4x4 208k miles
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post #6 of 6 (permalink) Old 08-26-2019, 06:06 PM
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Low batteries will cause a long cycle. If the fusible links were weak, there would be a very definite voltage drop as soon as you energize the relay.

1993 F-350 crew cab non-turbo 5 speed transmission
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