86 6.9 diesel glow plug problem

[jaymack77]

I have an '86 6.9 L diesel that is giving me hassles lately. The glow plugs work great when the light comes on, but I had to sometimes turn the key on and off twice to get the glow plug light to come on. When the light came on the plugs worked great. Recently it sometimes wouldn't come on at all and it has finally stopped working all together in the last week. I read through the forums and tried changing the controller (with another used one) and the light still wouldn't work. Is there some kind of relay? Will it not light up at all if some of the plugs are fried? Thanks in advance for your insight. I appreciate it.

[ModMech]

What the problem could be depends on whichof the three possible controllers you have.

The first two are basically the same, and screw into the left cylinder head at the very rear of the engine. There are MANY things that cause glow-plug problems with these. Best off to update them.

the last type bolts to the rear of the intake, and is fully transistorized. they are VERY reliable, but can suffer from corroded terminals at the controller, bad relays (serviceable part of the controller with squiggly strap bolted to it), and worn out plugs.

Yes, with the last system, if the plugs go out the controller will keep them on for a shorter time the more that do not work. Basically, if three do not work, or have very bad connections, the controller may not come on at all.

There is also the issue of the main connector at the RH side of the engine between the enigne and fender harness. If that 8 or 10 way connector gets corroded, you may not have enough power to the controller for it to function.

[Woodrow257]

You can ohm them out should read 2k if they are good

[jaymack77]

I checked the plugs with an engine voltage light, and 3 plugs are gone. I replaced the relay and it seems to be working properly now. I'll replace the glow plugs as a set in a bit. Thanks for your insight.