1986 6.9 IDI with no glow plug light and no start.

[Outlandyr]

How do, I have a 1986 F250 XL with a 6.9 IDI and I changed the flasher, oil/filter, fuel filter and air filter today. Unfortunately, I think I screwed myself because I left the ignition key on after checking the flashers.
Once I finished the maintenance service, I tried to start the beast and the glow plug light didn't go on and the truck wouldn't start. The truck came with a remote start.
I must have left the key in the on position for a couple hours. I didn't think it would matter as it's in the on position driving.
Anyways, I checked the relay, and putting 12v to the purple controller lead turns on the glow plug light, but doesn't seem to heat the plugs as the truck still won't start.
So, bad plugs or bad controller or both?
FYI, a little less than 53k original miles, so it likely has the original motorcraft glow plugs.
I did look for loose wires, wiggled the plugs and let is sit a while before checking a few times.
Any advice?

 

[DrCharles]

This may be a silly question, but have you checked to see if your batteries are dead? Leaving the key on will run them down...

Does the engine CRANK but not fire?

 

[Outlandyr]

Thanks, but it cranks just fine, it just won't start.
And, as stated, the glow plug light doesn't come on, unless I go direct from the + battery to where the purple controller lead connects to the glow plug relay.

 

[DrCharles]

OK. Is it possible that most or all of the glow plugs have failed from being left on/cycling for 2 hours? If you use a heavy lead to connect directly from the battery to the glow plug power stud on the relay, do you get a big spark and hot glow plugs (engine start)?

 

[Outlandyr]

I take it that is jumping from the battery terminal to the glow plug terminal: the 2 large terminals?

 

[DrCharles]

Yes.
If the truck was working before the key was left on, something must have burnt up. I seem to recall that the old 6.9 controller had a tendency to short, keeping the GPs on until they burn up (or run the battery down, or both)...

So if there's no spark, then measure the resistance at each glow plug with its wire disconnected. All should be nearly zero (a few tenths of an ohm, which is hard to measure with most pocket meters).

 

[Outlandyr]

There is good spark between the posts and very hot. I held for about 4-6 seconds and no start after jumping the terminals.
I'll have to test the glow plugs in the morning for resistance. I take it that higher resistance equates to a bad plug.

 

[DrCharles]

Correct... but that sounds like current being drawn by the plugs. May need to have someone else crank while you put power to the plugs...

Are any cylinders firing at all, or absolutely nothing but cranking? Fuel may be cut off. Check for power to the FSS on the pump (with key on, should be an audible click when the wire is connected and disconnected).

 

[Outlandyr]

Just cranking with no firing at all. With the glow plug light not coming on, I don't think it is a fuel issue, but I will check once I can pry her away from working on college financial paperwork with one of our boys.

As a related question, to convert to manual relay: where should I tie in the power from at the fuse box?
I'm thinking I could change out the glow plugs tomorrow and convert to manual glow plug relay as described wiring off the purple lead to an intermittent switch in the cab. I just wasn't sure where to wire in the 12v wire at the fuse box.
That would save me from having to replace the controller.

 

[DrCharles]

True, but it's very easy to burn out glow plugs with a manual switch. I like the controller on my 7.3 - works fine and also alerts you if a GP burns out by short-cycling. If you do replace yours I suggest converting to this later style controller. And always use Motorcraft/Beru glow plugs only. The parts-store Autolites not only won't last but are prone to swelling and sticking in the hole (and can break off in the head when extracted!)

Let us know what you find, I'm curious now

 

[Thewespaul]

Do you have any smoke coming out the tailpipe when cranking? You may have burnt up a fusible link and have no ignition. With the key on disconnect the front prong on top of the injection pump. You should have 12v there and here a solid click when you plug it back in.

 

[DrCharles]

great minds think alike... I mentioned the FSS power & click in post #8 Although leaving the key on for 2 hrs shouldn't hurt that circuit since it's always on while driving

I'm betting on a fried GP controller with some bad glow plugs - but I'd have expected to see a bit of smoke and an occasional cylinder sneeze too.

 

[Outlandyr]

Okay, a little light, a balky voltmeter, and 2 pulled Beru plugs later.
0 Ohms resistance, the plugs had a small amount of soot, but no significant wear.
The FSS does not click when unplugged and plugged back in, and there is no fuel smell or evidence of raw fuel exhaust at the tail pipe.

So, where would I find the fusible link in the wiring?
I don't want to mess too much with the harness given it's age and the plastic connections fragility.

Does anybody have a source on a replacement harness for the 6.9? (Eventually to be done, today I just need to find the fuse / fused section to change out. Then I can disconnect the controller at the purple lead once started to prevent a recurrence until I get the controller changed.)

 

[Thewespaul]

Your fusible links are coming off of the hot side of the starter solenoid. Check all your fuses first, then check the main connector for the engine harness on the passenger side of the engine near the dipstick, then investigate the fusible links. That main harness connector has a tendency to melt and you will loose power to the whole engine.

I’d say that your glow plug controller failed on, a few glow plugs started to short out which started pulling more current, which melted the harness connector or a fusible link. Once you get power to the injection pump, plug the block heater in for 20-30 minutes and disconnect the glow plug controller and see if it will start with just the heat from the block heater. Once you have it running double check your lights to make sure no other electrical circuits were damaged, then look into the glow plugs. I would not recommend replacing the controller with the same unit. Either upgrade to a solid state controller from a 7.3 or go with a manual control.

 

[Outlandyr]

It... LIVES!!!!!!
Sometimes, it's just that simple.
There is a fuse on the wire about 12" from the glow plug relay that is 20a.
It's in the top left of the picture with the relay in the bottom right.
So, I'll order a new controller. Accurate Diesel has one that looks good. Any opinions?
I'll also put in an intermittent switch for now and unplug the purple lead from the relay.