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Discussion Starter · #1 ·
I have an 86 f250 with a stock 6.9 idi. I just bought this truck 2 weeks ago so I'm still working out some bugs. After the truck starts, the glow plug light will come back on for a couple seconds then shut off. A click comes from the relay so I'm assuming they're still cycling with the truck running. I was wondering if this would go with the ignition switch or the relay. Any help would be appreciated. Thanks!
 

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Hey Buk_Wheat!

It sounds like the controller, located on the rear driver's side of the engine. The controller signals the relay to make and break the power according to temperature. Repair this ASAP or disconnect the switched wire from the relay immediately after start up and when the vehicle is off. If I remember correctly, my truck did this and burned up 8 brand new GP's in a day. I understand this malfunction is caused by age and the failed weather-stripping inside the hood. Rainwater dumps down on top of the controller and shorts it out. I believe this has been problematic to the design.

I corrected mine by bypassing the controller with a fused push-button switch to the control circuit of the relay. This works for me but may not be the best choice if you loan your vehicle out or use Colombo-style Valet service.

Lt Columbo2.jpg

Lt Columbo.jpg
 

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It's called afterglow; per the FSM it's normal controller operation. If that's what burned out anyone's glow plugs, every '83-'86 would have inop GPs.
 

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It's called afterglow; per the FSM it's normal controller operation. If that's what burned out anyone's glow plugs, every '83-'86 would have inop GPs.

I do not think so. Depending on how cold it is they will cycle for maybe a minute. My controller was telling the relay to energize my glow plugs while running on the highway for over an hour. It was raining cats and dogs. It was just luck that I looked down to see the indicator glowing from time to time.
 

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I will acknowledge that the Ford/Beru? glow plugs last the longest and deform the least. When your GP's deform due to failure, it is difficult to remove them or they break off and cause catastrophic engine damage.
 

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The OP indicates that it happens for a couple of seconds, not repeatedly. GPs re-energizing for a hour is a completely different issue, and yes, would definitely be bad for them.
 

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My controller was telling the relay to energize my glow plugs while running on the highway for over an hour.
The original poster didn't say anything about an hour. As Madpogue said, what you describe (buk_wheat) sounds like the normal cycling after the engine starts. My '91 has the improved system but it's basically the same and it cycles for 10 to 30+ seconds depending on the outside winter temps.
 

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If the OP searches, he (assumed) can find that this is a systemic problem with these controllers. As-a-whole you are correct.
 

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The clicking as described by OP is normal, I don't believe the WTS light should illuminate.
 

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Discussion Starter · #13 ·
Sorry didn't make it super clear. They continue cycling every couple seconds until i turn the truck off. Not just when i start it up. I disconnected the relay wire until I can look into replacing the controller.
 

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Sorry didn't make it super clear. They continue cycling every couple seconds until i turn the truck off. Not just when i start it up. I disconnected the relay wire until I can look into replacing the controller.
Apparently, I misunderstood you and missed the "couple of seconds" in your post. The GP's will cycle on and off, initially, when it is cold. This helps increase combustion temperatures and reduces emissions.

With that said, the controller near the firewall is susceptible to the failure condition I stated above.

Good luck and I am glad the discussion is corrected.
 

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IMHO don't waste your money on another stock type controller, just go to push button or better yet convert to a solid state controller .
 

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Get a new controller. rockauto has them pretty cheap. Thats where I got mine.

Why modify just because an old part failed?
 
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