‘86 6.9 glow plug question

This has happened twice now. I’ve gotten in the truck and when I went to cycle the glow plugs, it was like they had already started the cycle. Normally, I will turn the key to on and the plugs will come on for 5ish seconds. I can hear the clicks as they switch on then off. Then they will turn on and off intermittently for no longer than a second each time. This happens over the next 30 seconds. The owners manual said this is the normal cycle, so I wasn’t very concerned. Starts right up every time. Unless it’s about 15 degrees. Then I turn the key off for 60 seconds and reset the cycle and it starts just like normal. This is also what I read in the manual.

What’s changed lately is that when I go to cycle the plugs the first time, it’s like it begins in the middle of the normal cycle. (Turn key on. No plugs. Then plugs on and off for no more than a second each time) I can then turn the key off for 60 seconds and it will reset and they will cycle like normal. And start just fine.

Any ideas on what’s going on?

Mine did that.

Found out that one of them had a bad connection at the GP.

Yep, just one, caused it to act like that. And nothing wrong with the plug, just the connection.

Thanks! I’ll look into that in the daylight.

Selahdoor has a 7.3 controller. Unless your controller has been upgraded, it is different. It has a timer and a water temp switch in the controller. I'm pretty sure is dumb and doesn't know if anything is hooked up to it.

I would say that your controller is going out. If it decides to stick on, you want to know where the purple wire is on the relay behind the battery so you can pull it off and save your glow plugs.

The controller is screwed into the back of the drivers head. Known to break off when removing. Said to fail in the on position.

You can install a push button switch on that same purple wire and bypass the controller.

So when I bought the truck a few months back, the PO said, "It had some silly button that controlled the glow plugs," and that he had someone remove it and put it back to stock form. What I don't know, is if they upgraded to the 7.3 system or went back to the 6.9 system. Aside from location, how would I know which setup I have? I wish he had left the manual controls.

How many relays behind the battery?

Is there a relay with a small purple wire on the small post and two large orange wires heading toward the engine? If so, 6.9.

If the controller is mounted on the engine, it is a later model controller. It will have a relay on it. One side of it will have a z shaped piece of steel connected to the relay.

Easy to make your wishes come true once we know which system you have.

If it is your controller, which it very well could be if all connections are good, be careful taking it off. I’d suggest replacing it with the manual bypass button that you had on before that dude replaced it to stock like you said. I literally today just replaced all my glow plugs and then went to get the controller off and after letting it soak in pb blaster it broke off in the block :/ I’m about to post on here for advice on how to get it out but I will be converting to the bypass. If you want to buy the 6.9 controller OEM accuratediesel.com has a good deal on them and offer military discount as well good shipping costs.

Looks like it's the 6.9 controller. I'll start looking into going back to a manual controller. Thanks for all the help.

The terminals on the plug for the controller tend to loosen after 30 years. If a new controller is installed the terminals need to be pulled out of the plug and squeezed for a tighter fit.

Speaking of those connectors for the terminals...

Has anyone else noticed that those connectors are actually better connectors for the glow plugs, than the bullet connectors are? They grip the glow plug much better than a bullet connector.

Ok, now I am going to have to search for those connectors in bulk...

Selahdoor said:

Speaking of those connectors for the terminals...

Has anyone else noticed that those connectors are actually better connectors for the glow plugs, than the bullet connectors are? They grip the glow plug much better than a bullet connector.

Ok, now I am going to have to search for those connectors in bulk...

Click to expand...

While you're at it, please find female spades with the latch that goes in the male hole that locks them together like a couple of junkyard dogs.

No idea what to call either connector. So I am having no luck.