Hello everyone! Hope all is well.

So on my 89 Diesel F150, ever since I swapped that '86 6.9L in it almost 2 years ago, it's been burning the 2 rear glow plugs, #7 and #8, one of each every month to be exact... not as bad in summer, maybe one a month, but in winter and cold months, it's bad, the controller stays on way to long, 15-18 seconds when cold.

It is a new Autozone lifetime warranty controller, could it be a bad new controller or something else? Everything on that engine is new from 2 years ago including glow plug harness, it is swapped over to a 7.3 glow system.

All plugs are Motorcraft ZD9's, and it's always the 2 rear ones that burn?

I have that same controller on 3 other of my IDI's with no issues and they only stay on 10-12 seconds at the most no matter how cold, only 6-8 seconds in summer.

 

How are you determining they burn out?

15 seconds isn't too long for good glow plugs when very cold. These controllers cycle *shorter* when a plug dies, not longer, so I don't see a problem with your setup from that standpoint.

Edit: as far as the controller, it could absolutely be bad out of the box. That's par for the course these days!
But a few simple tests should prove that before just throwing parts at it.

 

Those are the shortest wires from the controller, aren't they?

I'd be checking the wiring resistance on all the /others/. Chances are, you have some corrosion or something not making good contact on other glow plugs, and the rear ones are getting hotter than they should because of it.

 

Aren't the GP wires some sort of special wire (fusable or something?) which would probably fail there instead of the GP? I'd think if a ground was messed up, it would force the current thru the shortest wires (like you are explaining), but the current would trash the wire instead of the GP?

 

Uh, the wires are just 10ga wire, as far as I can tell. I've never heard of glow plug wires failing, aside from the connectors coming off. No 'fusible link' there.

 

I knew I read this somewhere: https://www.ford-trucks.com/forums/1...g-harness.html

He uses "fusable link wire" to recreate the harness. maybe stock didn't have that, but it would be weird to invest that kind of money to recreate the harness if stock didn't require it.

 

Ahhhh, it's four posts down. He explains that the factory harness used fusable wiring. https://www.ford-trucks.com/forums/1...l#post10143012

If that's true, the John's 2 GP's overloading wouldn't mean a current issue, otherwise it would likely trip the fusable GP wires. But wiring can be weird and who knows why that's happening. Maybe John should clean up his block grounds.

 

Nice find, I've read that as well in a few places. Good thinking too.

 

I found this on a different forum:

The following examples of glow plug failure. Each example gives a different clue to glow plug failure analysis.

* There is no visible damage, but glow plug is electrically open. This indicates an internal element failure.

* Glow plug tip that is missing can be caused by incorrect timing or bad fuel.

* Multiple, distorted glow plugs are usually caused by electrical overheating. A complete evaluation of the glow plug control system should be made.

The tip missing is caused by overheating and/or the vibration of the combustion due to the timing being too advanced.

 

Being the shortest wires might mean something but I don't think it's that.

YIKES, sorry this post is so long!

The glow plugs are internally self regulating by design so they won't overheat. I am assuming that is with a properly working controller. I've read the Beru glow plug patents and they are unique. One of the special components aside from the alloys used in the coils, tip etc. is the formulation of the ceramic powder that is packed around the internal coils to prevent them from shorting out.- So they ARE different and better than other manufacturer's glow plugs in this application, at least for as long as those patents were maintained.) At least, they should work very well and last a long time with this controller.

Also there is an *afterglow cycle of up to two full minutes* in cold weather and it doesn't have to be very cold for that afterglow cycle to stay on for quite some time after start-up. After start-up the afterglow cycle begins and it's purpose is to REDUCE SMOKE and harmful emissions during warm up by adding heat into the combustion chambers for more efficient combustion, until the Engine reaches 'normal operating temperature.'

That 'normal operating temperature' is a coolant temperature of 112*F (44.444*C). .

People have argued with me in the past about that and said there is no way the controller can know what the engine coolant temperature is but I'll go by the book. That is what the 1987 Ford Factory Shop Manuals specifically state so that is what I accept as true.

From my recollection there IS a coolant temperature switch on the passenger side, which is NOT the temperature sender (or temperature switch) located on the Driver's side that goes to a temperature gauge AND/(OR) an engine overheat lamp on the instrument panel.

The temperature switch on the Passenger side, tells the rest of the components in that circuit that the engine coolant is up to temperature. For example, I think that switch controls the fast idle solenoid. If I remember correctly there are other sensors/ switches in that same circuit and the glow plug controller is also connected to that circuit.

Therefore I can only surmise that the ONLY way the controller can know that the engine is up to temperature and thus turn off the afterglow cycle is by the action of that temperature switch.

The FIRST thing that I thought about John's problem is that the controller is bad. NOW, I am wondering if it could be caused by a bad temperature switch on the Passenger side. If that switch doesn't work, HOW is the rest of the system going to know that the engine is up to operating temperature?? HQW is the Glow Plug controller going to know??

If I'm right about all (or most) of the above then my second reasoning is that a failed temperature switch will result in the glow plug controller keeping the afterglow cycle ON for 2 full minutes after every start up, no matter if the engine is cold or hot. The afterglow is supposed to turn off after 2 minutes regardless of engine temp but the entire cycle from initial glow of 10-15 seconds for start up, followed by an afterglow cycle of up to two full minutes, starts over again at the beginning every time the engine is re-started.

If this is the case (bad temp switch) then I speculate that the glow plugs are just taking a lot of extra and unnecessary abuse and it may be the back ones going out first because they are closest to the controller. Due to the high current draw of all 8 glow plugs the back ones may be the first to heat up to full glow (speculation on my part) and thus they may be the ones that stay on the longest and fail first. (I'm just thinking and writing my thoughts).

What I would do is TEST that temperature switch and replace it if it's bad. If the fast idle solenoid is not working that would be a big clue.

If it's not that, then I am back to 'the controller being defective.'

Next, a problem in the glow plug wires.

Another thing: in cold, to very cold weather, I would block off outside air flow to the radiator during warm up and especially if you have a large auxiliary transmission cooler for an automatic transmission.

That would reduce the work load on the controller and glow plugs, even though it should be handling this without problems with a normal 'stock' cooling system. I have a large aux. transmission cooler (which I will need later in a hotter climate zones) and my engine is slow to warm up even when the outside temperature is above freezing. Eventually I'll probably put a thermostatic control in the aux. transmission cooler line. Meanwhile I am still trying to figure out a very simple and convenient way to block outside airflow to the radiator during warm up.

I've read that it is NOT good to leave a diesel engine idling too long for a warm up and that normally you should start driving at after about 30 seconds. I don't know at all if that applies to these old IDI engines but my biggest concern is that the automatic transmission is warmed up before I start driving. Especially with a larger auxiliary transmission cooler.

I don't know how to fully test if the controller is working properly through it's functions. I personally would not be satisfied in only knowing that it turns on and off with the ignition key. That doesn't tell me much about the afterglow cycle and if it is working properly or cutting off when it should.

I don't even want to begin talking about the mystery of exactly what is inside of these sealed solid state controllers and exactly how they work or I'll write another page and still not know.

I couldn't find any patents for the controller and I have no idea who designed and manufactured them. All I've seen is comments from electronics people like "This is normally how a controller works," and I saw one patent schematic of a solid state controller (not this one) and one simple sketch of a solid state controller circuit.

So, after all of that writing I'll have to say that I'm basically making wild-a*$ guess as to what's causing the problem.

I just hope you get it fixed, John

 

From what you just wrote, I agree IF that is true (fusible link wire) with JOHN's glow plug harness then it has to be either defective glow plugs or the controller and relay isn't working properly.

With a current overload, fusible link wire is supposed to melt all the way through to protect the wiring and components in the circuit from damage, over heating and fire. The special insulation contains it so it doesn't start a fire.

Why would they not have used a single fusible link instead of fuse link wire for the harness? I see: 1) If there is a dead short at a single glow plug terminal for example, just that one GP wire will melt through to open that one wire connection and the rest of the wires will remain closed circuit and work. 2) People tend to cut out and bypass a failed fusible link and splice the wires directly. That can lead to serious wiring/component damage and electrical fires. Fusible link wire would prevent that from happening.

OK, that makes a lot of sense.

I remember that topic and the 'fusible link wire' too. As have some others, I think I've read practically every post on every diesel forum on IDI era glow plugs and solid state controllers as well as spent lots of time reading research abstracts and patents etc. going back to the early 1900's. It's crazy (like a mental disorder) the amount of time I've spent researching this sort of stuff and I can't seem to pull out of this insanity. (That's an honest admission).

I can't say that I know anything more than I've already posted. I was dissuaded from following that 'fusible link wire' recommendation because I've seen where others (i.e. youtube) have opened an old original harness, bought new wire to match it and made the harnesses out of regular wire without any mention of 'fusible link wire' or 'resistance wire' as some have called it.

I re-read post number 4 and I just checked that original poster's profile and he wrote under 'interests' "Particle Theory" Well, that goes right down to and beyond the science of electricity; electrons, protons, and neutrons etc. into sub-atomic particles and theoretical physics (which I am not hugely interested in) so he probably was competent to understand what was written on the harness wires but STILL there is no supporting confirmation that it's true and quite frankly I've known a few people who had exotic interests including theoretical physics similar to "Particle Physics" who would have difficulty figuring out which way to screw a light bulb in or how to replace a light switch on a wall. I wish he would have taken a picture of that.

But in theory it makes very good sense so I am just going to trust what that guy said, until I see someone else (or myself) confirm it or not.

I'll have to read some other posts and give this some more thought tomorrow after I get some badly needed sleep.

 

you are partially correct. the temp sensor in the passenger side head does control the fast idle, timing advance, but not glow plug controller shut off.
if the sensor is bad, it will not activate the fast idle or timing advance, but the glow plug controller will still work properly.
that is controlled by the other temp sensor.
the reason i know this is because my passenger side sensor was unplugged for over 200,000 miles and the glow plugs still worked properly.

 

Just want to point out that 'fusible link wire' is just standard copper wire, with a high temp, fire-resistant insulation. You use a piece of this wire 4 awg smaller than the wire you want to protect, so it burns out first.

So, as far as I can tell, if you use the same AWG fusible link wire instead of regular wire, you get... high temp insulation. Not a bad thing, but it shouldn't affect the operation of the glow plugs either.

When I built my own harness for my tan 88, I just used 10ga trailer wiring(I had a lot of pink and green). I routed them /forward/, and then over the passenger side just behind the alternator, to a relay on the fender well plate.

I found that in an overheat situation, the /front/ two burned out before the rest. These two had the shortest wires in my setup, by just a couple of inches... but I guess it was enough.

 

The service manual has some good info on the fusible link wire that makes me a little nervous. They sort of ran it everywhere around my van with the factory. They also give an example of how to patch some fusible link patched into a broken fuse link wire.

Now, I noticed the fusible link wire to my glow plug controller is a yellow pair marked fusible link and connected at the battery side of starter relay. My glow plug wires look like regular 12 gauge or 14 gauge to each plug. the glow plug wire off the controller is brown to the plugs. I don't know if that's a fusible link. manual says the fusible link is the yellow wire.

The low idle solenoid and cold advance solenoid are activated by an engine temperature switch supplied by 12V power from the switch. that also supplies power to tell the controller the switch is on.

Manual says the glow plugs will be activated for up to 15 seconds then power cut by the controller to plugs. Engine can start. Then Controller will monitor glow plug temperature by measuring resistance of glow plugs and then will cycle on the glow plugs for up to two minutes when they cool below a threshold to keep fuel burning cleaner during power on. This is accomplished with the PTC glow plugs. THe glow plug controller has a built in engine temp sensor thus mounted on the back of engine to determine if glow is needed when starting engine.

My successful glow plug controller manual bypass(bad controller) and I activate the plugs for 15 seconds when cold and the engine fires right up. I let go and that's it engine running. When hot, no need for glow plugs.

 

They burn out, quit working, I take 'em out, try them directly on the battery and nothing.

15 isn't to bad I agree, but this one holds them on for 18+ seconds at times, most times actually. I find that a little long, compared to all my other IDI's witch start up just as quick with only 12-14 seconds when really cold.

I will check the grounds, and if nothing wrong, I'll replace that controller.