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Brand new glow plugs fried?

6K views 31 replies 6 participants last post by  Gossetttt 
#1 ·
So I had a friend install new GPs and I had him use the snow plow relay that I had read about here.

Everything worked great at first, but then the truck stopped starting again.

I can now start it only with ether or when plugged in.

I tested the posts on the relay, and learned the following:

one side is hot always.

Turn the key for WTS, and the other side becomes hot.

It stays hot after the WTS light goes off, and stays hot even while the truck is running.

I assume either the relay was bad, or more likely the computer is telling the relay to stay engaged.

I further assume that my brand new glow plugs are now toast.

My buddy who did the work for me says that even if the relay were installed backwards, it should have no effect.

How can I further trouble shoot / diagnose the root of this problem?

This guy is a 20+ year diesel tech, though mostly with the Dodge. He thinks this may need dealer type computer diagnostics, but I figured that I would start here.

Thanks,
 
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#2 ·
The relay will stay on for up to 2 minutes after you turn the key on to run before it will shut off. So if it is staying on past this time frame then there is a problem with the wiring or the PCM. The PCM provides the ground signal to the relay.

What brand of glow plugs did you install. Most have found that the only ones to use are the Motorcraft ZD-11's.
 
#3 ·
Also, what brand of Glowplug relay was installed? If the relay is not a case-isolated type (meaning none of the posts, large or small, should have any continuity with the base), the plugs will also not turn off. Cheers!
 
#4 ·
Thanks guys. The relay did shut off after a couple minutes. I did not check to see if it had any continuity with the base.

What else can I self diagnose with just a multi meter?

It wouldn't even think about starting at 40 degrees without being plugged in. Plugged in it starts immediately, but that heater must pull a lot of amps. If I have much else going, it blows the 20 amp fuse.
 
#6 ·
Thanks guys. Plugged in it starts immediately, but that heater must pull a lot of amps. If I have much else going, it blows the 20 amp fuse.
How long is your extension cord and what gauge is it?

Amps = Watts / Volts
 
#5 ·
What brand of glow plugs did you or your mechanic install?

Have you tested them through the valve cover gaskets to see if they are bad or not?

How is the under valve cover wiring?

I would also do a voltage test on the relay to make sure that it isn't burnt or bad.

The heater is 1000 watts and the formula for converting watts to amps escapes my mind right now but it will be around 10 amps.
 
#7 · (Edited)
I don't know what brand he used, aside from that they came form NAPA.


He did replace the wiring.

I do not know how to test the plugs themselves.

I should probably run a shorter cord, but it is a 12 gauge 100 foot cord. . I wouldn't think that would add much resistance to the load. 30 ' would do the trick.

The pig tail coming out of the hood looks like a 14 if not 16 gauge cord, and it is green, which I assume is not OEM.

I can't really see where it might be spliced in, but it doesn't look to be adding any length.

People act like 1000 watts isn't that much power. Most of my light bulbs in my house are 40-60 watts, if they are not CFLs, which probably only draw 15 watts.

1000 watt load is the equivalent of leaving 20, 40-60 watt bulbs running, which I try pretty hard not to do.

This is a second or third vehicle for us, with a big camper on it. Leaving it plugged does not need to happen very often, but I sure as heck can't drive it up skiing right now and expect to drive home.
 
#8 · (Edited)
I should probably run a shorter cord, but it is a 12 gauge 100 foot cord. . I wouldn't think that would add much resistance to the load. 30 ' would do the trick.

People act like 1000 watts isn't that much power.
A 100' 12-gauge cord is rated to a max of 14-15 Amps. My OEM Block Heater pulls 15-16 Amps continuous use. I would agree with you that a shorter cord would do the trick.

Many forum members keep their block heater on a timer set to turn on 3-hours before they need the truck.
But that won't help at the ski area.
 
#9 ·
While NAPA stocks glow plugs that will work in our trucks they don't stock the factory ones and there has been problems with just about any glow plug other than what is stock for our trucks.

So I would test them through the valve cover gaskets and if they are bad then I would replace them with Motorcraft ZD-11 glow plugs and nothing else.
 
#10 ·
Bugman,
Are the UVCH connections a problem on these earlier 7.3's like they are for my 2000 MY ?
 
#11 ·
No the harness is no problem keeping them connected but they just like to cook the harness connections at the valve covers. International used to make a repair kit for them but I don't know if the kit is still available.
 
#12 ·
OK.
Since the OP has new GPs and his GPR tested good, is it possible there is a problem with the harness connection you mention?
 
#13 ·
For some reason these trucks don't like aftermarket glow plugs, they tend to eat them. I don't know if it is the extended time that they are on after starting or what. So if they are indeed dead or bad he needs to replace them with some ZD-11's.

All this can be figured out by testing them. It also sounds like he is depending on his mechanic to do the work.
 
#14 ·
Thanks guys. Can someone point me towards how to test the glow plugs? Seems the relay is acting as it should.

Hard to believe they would be burned out after jut a couple hundred miles, if they are not stuck on.
 
#16 ·
For checking the injector/glowplug wiring: From each valvecover gasket connection's outermost pins (2 per connector) to ground you should get 0.1 to 2 ohms (indicates good plug and wiring). From each valvecover gasket connection's center pin to each immediately adjacent pin, you should get around 3 ohms (indicates good injector solenoid and wiring). You should not get any continuity from any of the outer pins to the 3 inner pins (indicates no shorts between injector and glowplug wiring). You should also get 0 to 1 ohms from each of the external harness connectors outer pins back to the Glowplug Relay's large terminal on the GP side (indicates good wiring from external connections back to the relay).

To check the glowplug relay (GPR), measure the voltage drop across the GPR's large terminals. While the GPR is active (up to 1.5 to 2 minutes after the key is turned to Wait-to-Start) put your meter leads on the large terminals (one lead on one large terminal and the other lead on the other large terminal). The measures how much voltage is being "lost" across the relay. A reading of 0.3V or more indicates a bad relay.

Cheers!
 
#17 ·
Thanks for your help folks.

Snow, I watch some of the Utube stuff that came up on your google search.

I think I've learned that my valve cover wiring is suspect.

When I put the Ohm meter to the GP points in the valve cover, I get no continuity to the neg battery terminal on any of the passenger side gps.

I didn't try the driver side, as the plug didn't want to cooperate, and I didn't want to risk cracking it.

Can anyone direct me to a reliable, value oriented vendor for getting these?

I've got a buddy who is going to help me do this next weekend.

I think I should probably have a new set of GPs on hand just in case, but it seems likely that my new ones are still good.

The guy who did this work for me, knows that he got Motorcraft GPs from NAPA; he does not remember if they were the ones you guys have suggested.

Anything else I should be replacing while the valve covers are off AGAIN?
 
#18 ·
The first thing that I would do is to pull the valve cover off and take a look at the wiring and then measure the glow plugs with out having the harness connected.

For parts I would go with Motorcraft only. Parts stores stock Dorman gaskets and wire harnesses but this is one thing that you only want to do once. K-Manns Parts stock everything that you would need if you decide to go with Motorcraft and their prices are not that bad.

If you pull one of the valve covers you may be able to eliminate the costly gaskets and perhaps the plugs themselves if it is the wire harness. Other than that I would purchase the glow plug replacement kit that they have for $369.00 which has everything in it.
 
#19 ·
Tore into this last night with a mechanic friend.

I bought new glow plugs and the valve cover gasket/ wire harnesses ahead of time.

Found 7 of 8 glow plugs dead. (eighth one might not have been plugged in tight enough to have been engaging at all.

gaskets and wiring looked and tested great, but I put the new ones in just to be safe.

He did the first side, while I did the driver's side after watching him start.

The hardest part, aside from the bolts in the rear that were hard to reach, was pushing the plug wire back onto the glow plugs.

Got it back together and realized the signal to the relay was not shutting off, at least not always, hence the brand new burnt plugs.

Seems like an obvious thing to test, but maybe that isn't SOP?

It was getting late, and diagnosing the cause of that problem was not on the agenda.

We rigged a switch to the control wire, so I can cut power to the relay once its started.

So far so good. I'm getting a Momentary switch that requires holding down, to ensure it cannot be left on.

I am wondering how I would diagnose the issue that is leaving the control wire to the relaly hot, after WTS goes off.

I am also thinking that I should just bypass that power source entirely and make the power to the relay fully manual via the monetary switch.

Any reason not to do that?

I know the GPs cycle on and off while warming up. How important is that? How long and often would I hold them on to mimic that?

What does it accomplish aside form reducing emissions? (nothing reduces this thing's emissions, yet it passed with no issues.)

Thanks,

Dave
 
#20 · (Edited)
Dave,

The GPR can cycle ON & OFF for atleast 90 seconds after the Wait To Start light turns off and the engine is running.

It does this by design.

Are you sure this is not all that was happening?
 
#21 ·
Just as a FYI the wait to start light is just a idiot light and really has nothing to do with the glow plugs or the glow plug relay, and is just there to make you wait a while on cold starts.

Mr. Driver, it is my understanding that the old 6.9 engine would cycle the glow plugs on and off for a while but on the computer controlled Power Stroke engine it doesn't cycle. But the PCM will keep the glow plug relay energized for up to 2 minutes to burn off carbon that is built up on the plugs during cold starts.

Now back to Mr. Franks, if the relay is staying energized longer than 2 minutes there could be a number of problems. One could be that it is the wrong relay. There were a number of parts store relays that were sold as a direct replacement relay for our engines that were case grounded and would stay on as long as the key was on. Another problem could be a grounded signal wire from the PCM which would keep the relay on as long as the key is turned on. The other could be a bad PCM that is constantly sending out the ground signal to the relay.
 
#22 · (Edited)
@DFrank. What Mr Bugman says based on MY^^^^I had thought early 7.3s were still like my old 6.9.

When you have a chance, you might list your vehicle specs in the Signature.

With 8 new GPs you should now be able to go skiing ;-)
 
#23 ·
I'm pretty sure the relay is good. If kill the control wire powering it, (which is what I've interrupted with my switch) the relay shuts the power side off.)

The control wire does sometimes quit sending signal to the relay, but it was still on after what seemed like three minutes, in the shop warm.

How long is it OK for the GPs to stay on? I don't want to burn out another set.

The first set was not Motorcraft, but Autolite, I believe, and they all got fried quickly, I assume form being left on.

Maybe I'm being paranoid, but I think control wire to the relay is at least sporadically staying powered up. I can check this safely now that I can bypass that and ensure that the GPs are off.

It is a 96 F350, Crew cab, 4x4 with 280K miles. I will add that to the sig line later.

Thanks,
 
#24 ·
The relay will have 12 volts to it as long as the key is turned on, that wire is what I believe that you have put your switch in. The relay is activated when it gets its ground from the PCM.

So the wire that you are saying is the control wire is always hot with the key on and that is normal.
 
#25 ·
Thanks Bugman.

So if what you say is true, what turns the glow plugs off, and how long is it ok for the to stay on, without risking another burn out.
 
#26 ·
The PCM will remove the ground it provided (at pin 101) and the GPR contacts will switch back to OPEN. The glowplugs will stay on for up to 2 minutes after the key is turned to WTS. Cheers!
 
#27 · (Edited)
Thanks Patrick. So assuming my PCM is sending the wrong message, is there any reason not to just run it how I have it?

I am not actually sure if I have interrupted the ground side or the hot side, though I do know how to test for that. I think I am on the hot side.

Seems like I should remove the PCM ground, and run my own switched ground. Then I'd have full control over the glow plugs and just need to know how long I should be running them, and whether it is important to keep cycling on warm up and how to mimic what it wants.

I only drive this rig for weekend camping trips, so its not like I need to go warm it up every day, I just need it to be able to start when not plugged in at the end of a ski day in the mountains. At home I'll usually plug it in for planned trips, and then not even use the GPs, right?

The switch I got is rated for 3 amps @12Vdc. It is a momentary switch, so I can't leave them on by mistake. Any reason this is not sufficient? (this is to replace the on/ off button that is on it now, that could be left on any mistake)
 
#28 ·
Haven't some guys wired up a small LED in the cab that lights up whenever the GPs are energized?

Has it ever actually been confirmed that the GPs were remaining on all the time?

It seems like a diagnosis was made the first night your mechanic buddy helped you out and you wired a bypass but could you remind me how you know the GPs are staying on.
 
#30 ·
AD, you are correct, that I am not sure that they always stay on, just that they sometimes are on longer than two minutes, and with blowing a set after just a few days of driving, I want taking any chances.

Maybe I should wire an LED as you suggest, fed bu the GPR, leave the switch as I have it presently (ON/OFF buttons) and get a better feel for how often/ long they may be staying on by themselves.

What else might cause GPs to fail in just a few hundred miles of driving?
 
#31 ·
So I wird in an LED to the hot side that powers the GPs.

I do not fully understand what is happening with the control wires.

If I understand correctly, there is one small and one large wire to the relay that are always hot.

The other large wire feeds power to the GPs when told to by the other small wire.

Here is where I get fuzzy: The second small wire is not hot when the truck is off. From reading Patrick's post, the other small wire is actually a ground, that the PCM ones and closes if thats the right way to describe it.

If this wire is just providing ground to the really to close that circuit, why am I getting voltage there, even when the really has shut off? This wire still reads battery voltage, after the really has opened or shut the GPs off.

As I write this I am understanding that the post would stay hot, just from the other post, and that the circuit is not grounded via the PCm, and that is how it shuts down.

The glow plugs do seem to be shutting off at least at present.

I know this both through watching my new light in the cab shut off, as well as testing the post on the relay with a volt meter, just to confirm that the light didn't burn out as soon as I hooked it up.


I guess I'll just leave my cut off switch closed and and watch my new light to see if they ever stay on again.

What else would burn these out so fast?

Can it be as simple as the Auto light GPs that were initially installed, are so poor that they failed in less than a dozen start cycles?

Would they have gotten extra power do to the 8th one not being hooked up? ( the wore hadn't been on tight enough and rattled loose maybe) This one had not blown, as it probably never saw power.

My first mechanic said they came in a motorcraft box, from Napa.

The ones I just got came in individual bags that had the ZD11 model labeled, or whatever was recommended in this thread earlier.


Thanks for your help and patience.
 
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