Glow plug troubles

Jay Krout

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So Ive got a 1990 F Super Duty with a 7.3 IDI motor, no turbo and basically a stock motor, no turbo no turnin up the screw inside the pump or anything else that I can think of. This is my weld rig and I make my living with this.

Glow plugs took a crap about a month or so ago, earlier this week I put a new controller and relay in and new glow plugs. The way it acted the wait to start light blinks once goes out and the relay clicks for a bit then stops crank it up it will crank awhile til she lights up, thats the way it acted before the new goodies and still continues to do so.

Ive checked the plugs there is continuity to all of them and continuity to all the plug wires and I checked the voltage at the wires and Ive got a bit over 12 volts, maybe 12.3 to 12.6 on all the wires, and over
12 volts for the ignition test as well.

Now Im thinkin of putting a push button switch in the dash and bypassing the process but I need a wiring diagram to follow to wire it up...Im not much of an electrical guy the most I know about electricity is what is happening at the end of that weld rod.

Ive searched on google and here and from what I can tell there is a few ways to do it, but this scares me I dont wanna burn up the truck 3 weeks after I do this, I know one fella who did this and the truck caught fire when he was parked at the house for the night, I dont wanna be that guy.

So If any of you fellas or ladies can provide a drawing of some sort it would be greatly appreciated. I like blueprints and drawings, seems to go much better for me than an explanation.

Thank you all very much

Jay Krout
Popeye

This is my weld rig

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TNBrett

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I wouldn’t abandon the glow plug controller just yet. If it’s short cycling like that with a new controller and new glow plugs perhaps the issue is in the glow plug harness. If the connectors aren’t making good contact with the glow plugs themselves, it could short cycle and not heat up long enough to be effective. As you may already know, this is what happens when even just one or two glow plugs burn out. The problem here is if all you do is a manual bypass, you could still have an issue where you’re not heating all of the plugs, and it still won’t start like it should.


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Jay Krout

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But why is it then that Ive got 12 volts at all wires that go on the plugs? Ive also got 12 volts on the ignition post. Evrything seems to check out fine according to this book I been using. Only thing ive seen different from that book is they want you to put the test light on the test terminal the one on top with the resister thing (the sqiggly bar that goes down to the bottom) on it with the ignition switch off, if I do that I get no power to the wires, i turn the key on or use the post on the other corner Ive got juice that way, Im wondering if its a misprint in the book. But even when it was workin it wouldnt light on the post. This happens evry year and I put another controller and relay on and that fixes it up, so I checked it using the post with the squiggly thing...(shunt resistor?) and it wont give me power there.

Im sure its probly something simple and stupid, but Im tired of dealing wioth this evry year

Thank you for your input I will keep seein what I come up with testing this stuff

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TNBrett

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The system is very sensitive to resistance. If the connector that goes on the plug is not making good contact, then the resistance will be higher. This will make the controller think the plugs are hot, and it will short cycle them. You would still see 12 volts at the connector, but the plug won’t.

Maybe snap a pic of the wiring at the controller and post it for us.

Are you running Motorcraft zd9 glow plugs?


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Jay Krout

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The glow plugs are the ones from Ford it says ZD-9 on the pack and Beru on the plug itself so Im pretty sure I got the good ones. I will have to figure a way to put a picture of the connections on here. I took them off and put them back the way they were hooked up when I bought this truck and checked the diagram in the book it checks out. As far as the connections to plugs go I can squeeze the connectors a little bit and see if that will make em tighter and put some dialectric grease on them.

Thank you,

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Jay Krout

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OK I gave each of the wires a little squeeze, I dont think it was needed they were all pretty snug on the glow plugs, and I put a little bit of dielectric grease on each one of the plugs it didnt make a difference.

I took a picture with a digital camra but I cant figure out how to load it onto this computer, wish I was a bit more tech savvy but Im not and I dont have one of those new phones either.

I will research the bypass thing a bit more Im just tired of messin with this thing

Thank you
Popeye
 

IDIBRONCO

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I took a picture with a digital camra but I cant figure out how to load it onto this computer, wish I was a bit more tech savvy but Im not and I dont have one of those new phones either.
This sounds just like me. I do the same thing. As for the manual bypass on the controller, all you have to do is to run your push button to a ground and then run the other side to the white wire than comes off of your controller. Cut the white wire first so that it only makes contact with ground when you push your button. Just remember, like TNBrett mentioned, that may not fix your issue if there's something else involved.
 

Big Bart

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Jay,

What generally causes the glow plugs to only go on for a short period of time (1-2 seconds.) is when there is a resistance (OHM, a short/open circuit.) problem between the controller and ALL of the glow plugs. If the controller thinks 3 or more glowplugs are bad. (Based on overall OHM resistance.) Then it just goes on and imediately off. The glow plug wiring harness is known to go bad in these so often that is part of the problem with getting a good OHM rating to the controller. (I would also guess if the wiring supplying power for the glow plugs is compromised it could possibly fool the system as well. Just a theory.)

So let's recap and go from there.

1) You have installed a new glow plug controller.
2) You have installed a new set of Ford glow plugs.
3) You have tested to see if you have voltage via the glow plug wiring harness and you do at each glow plug connector.
4) You have squeezed the glow plug connectors a little to see if that will help.
5) You mentioned you have continuity but did not mention between what. Or what your contuniuty test came back as. So give us an explaination of your test and results if you do not mind doing so.
6) You still have the same issue, the controller only comes on briefly, then goes out. (Seems to cycle on and off.)

Some questions

1) Did you put anything on the glow plug threads when you put them in the engine. (Such as anti-seize, thread sealant, plumbers tape, or ????)
2) Did you check to make sure the glow plugs have a good OHM test number after you installed them? (Perhaps you got a couple of bad ones, never assume new parts are working!)
3) Did you clean up all your connectors and wiring before re-attaching to the glow plug relay/controller system?
4) Did you replace the glow plug controller and the glow plug relay as a set? Or did you pull in two and do half of it?

Let us know and we can then suggest some more ideas. Personaly I would fix what is in there but a bypass via a switch seems to work for many on this site.

In the short term here are some other resources for you to read up on to perhpas give you some more thoughts on the issue. Also help you with your wiring question.

http://www.garysgaragemahal.com/start--glow-plug-control---diesel.html

http://www.intellidog.com/dieselmann/idi.htm

https://classicdieseldesigns.com/co...n-turbo-location-glowplug-replacement-harness
 
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TNBrett

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Maybe check your ground connection for the controller. That may be enough for the controller to not see what it needs to function correctly.


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HS108

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I think you need a new wiring harness for the glow plugs,

Even tho it may look good, the wires inside can be shot, that’s a lot of heat they take on top of the motor like that.

From your list of everything you have replaced I don’t see a wire kit on there, yes you may have the 12v and the plug is fine, but you could have a short when it’s at full load, or the wires can’t handle it, causing the controller and plugs to short cycle, and causing an early death for them time and time again.

Check out classic diesel designs, get a good quality kit for a decent price, and Wes the owner can probably help ya with some advice as well.


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Jeremy 1970idi

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I've replace my glow plugs first time around with a brand new controller on my 1986 f250 idi n/a. The controller would click and then shut off. Turns out the gauge of wire on the two cables going back to the battery was wrong. I put new 10 gauge wires from the controller to the battery and still just clicked. Turns out, the system is so sensitive that mine anyways only works with genuine ford oem glow plugs. I put new OEM ford glow plugs in and boom , works perfect. I first bought Bosch plugs and didn't work, then put the Ford ones in and it works every time now.
 

Jeremy 1970idi

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im just saying before you scrap the whole set up. Take $10 in wire and feed your controller new power wires. I had 12v to my controller too but the wires couldn't handle the amps. it melted. I found a melted wire in the harness. I would suggest feeding new power to the controller and go from there.
 

Lawrence Koepke

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Another vote for wires. The glow plug controller wires and the connector buried in the harness have caused many an IDI to fail to start as they age.

I have a 1991 F350 Lariat Crew Cab, and I found high resistance in the connector that is in the middle of the harness, feeding voltage to the controller. I spliced in heavy gauge wire to bypass that connector, and my problems went away, for a while. Then, last year, one of the wires feeding 12 V to the controller got warm enough to soften its insulation and the insulation on the blue ignition wire adjacent to it in the harness, constantly supplying 12 V to the fuel shut off solenoid (FSS). Imagine my face when I turned the key off and the engine kept running!

My solution was to remove the wires that supply 12 V to the controller, and replace them with a single length of battery cable wire. Since that also eliminated the fusible links, I bought a big AMG fuse to put on the starter solenoid hot post, and bolted the new wire (with battery terminal lug) to the other end. Problem Solved (forever).
 
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