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Discussion Starter #1 (Edited)
Thought I'd post this as a sticky thread now that cold weather is on us.

How to check Glow Plug System

To check the Glow Plug Relay (GPR)
· Be sure the engine is cold, so that the PCM will tell the GPR to turn on. If the engine is hot, you won’t have as much time to check. (if oil temp is above 130F, it won't turn on at all)
· Locate the GPR – It's behind the fuel filter on top of the engine, a little bit toward the passenger side of the valley. There may be two relays there. If so, the rear one is the GPR. It will have two fairly large wires (yellow and brown) connected to the large post without the rubber boot.
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Another location photo here:
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Photo credit F350_6
· With your multitmeter set to DC volts, and 15 V range (if not autoranging), clip the positive (red) lead to the output terminal (with yellow and brown wires connected), and the negative (black) lead to a good ground point (like the battery ground terminal or someplace metal directly on the engine block.)
· Turn the key to ON (do not start)
· If your GPR is good, it should click, and you’ll see 11 volts or so on your meter, then, depending on temperature, it will click off up to 2 minutes later. You should do this a couple of times to make sure it consistently makes the connection.
· If you don’t get voltage with this test, confirm by retesting as follows.
· Remove the two small wires from the smaller two of the four GPR terminals.
· With jumper wires, apply voltage from the battery across the two small terminals. If your voltmeter now reads voltage on the output terminal, your GPR is OK, and your problem is in the PCM circuit that tells the GPR to activate.

GPR for 99 & up 7.3L
Ford F81Z-12B533-AC
NAPA GPR#109 (mounts 90 deg out of rotation from original)
Carquest #RY-175 (clone of GPR#109)
Autozone Sorensen MR-99 (also clone of GPR #109 I think)
International #1831646C1 (Identical to the one you'll get from Ford) ~$25-$30


To check Glow Plugs.
· Remove the electrical connector on the inboard side of valve cover at the gasket. Press down on the top of the connector latch and pry gently with a screwdriver.
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Disconnecting VC harness connector.
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Another photo of it loose.

· There will be 9 pins on the valve cover gasket where you removed the connector. The two pins furthest forward and the two pins furthest back are for your glow plugs.
· With your multimeter set to resistance (ohms) and low range (single digits) if not autoranging, clip the negative (black) lead to a good ground point.
· Probe each of the 4 outer pins individually with the positive (red) lead, noting the resistance. Good glow plugs will have a resistance between 0.6 and 2 ohms. If you get infinite resistance on any glow plug, that one is either bad or the connector under the valve cover has come loose.
 

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Good Post. Keep em coming..... And thanks for taking the time to share that..... /ubbthreads/images/graemlins/biggrin.gif
 

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Oooohhhhh. This is awesome. We've had Ford diesels for years, and are just now trying to figure out what we can do on our own! (I'm sick of paying the "stealer" his crazy rates) This kind of troubleshooting is AWESOME! Please, please, please keep it coming!!
Is there any way to post diagrams? I know, I should just get the repair manual...... But I'm still looking for the fuel filter....
 

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Discussion Starter #4 (Edited)
But I'm still looking for the fuel filter....
LOL /ubbthreads/images/graemlins/biggrin.gif /ubbthreads/images/graemlins/biggrin.gif

I know what you mean. The owner's manual on my 99 doesn't even tell you where the filter is. /ubbthreads/images/graemlins/mad.gif

I eventually found it under the "Powerstroke" cover on top of the engine. We were all noobies once. /ubbthreads/images/graemlins/grin.gif
 

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[ QUOTE ]
[ QUOTE ]
But I'm still looking for the fuel filter....

[/ QUOTE ]

LOL /ubbthreads/images/graemlins/biggrin.gif /ubbthreads/images/graemlins/biggrin.gif

I know what you mean. The owner's manual on my 99 doesn't even tell you where the filter is. /ubbthreads/images/graemlins/mad.gif

I eventually found it under the "Powerstroke" cover on top of the engine. We were all noobies once. /ubbthreads/images/graemlins/grin.gif

[/ QUOTE ]

This is information that needs to be added to the beginning of the otherwise great write-up in the "The TheDieselStop.com 1999-up FAQ" I copied this off and had it in hand when I went to R&R the fuel filter but my wife and I both looked for quite some time before I figured out where it was located.
 

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Thanks "klhansen" and "8V92TTA" for the great write-ups and the additional diagrams. I'll add all this info to my "book" of PSD knowledge for use in the future. /ubbthreads/images/graemlins/cool.gif
 

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KLH, so how do ya know if your GPR is faulty? Thanks!
 

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Will it still start in warm weather with a faulty GPR? Do they completely fail or get tempermental??? Good Stuff /ubbthreads/images/graemlins/cool.gif
 

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What if you have a CA truck and have the Glow Plug Controller instead of the Glow Plug Relay? How would I go about testing this thing? It has 2 pigtail plugs goin into it...Thanks!
 

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Discussion Starter #12
[ QUOTE ]
What if you have a CA truck and have the Glow Plug Controller instead of the Glow Plug Relay? How would I go about testing this thing? It has 2 pigtail plugs goin into it...Thanks!

[/ QUOTE ]

As far as I know, the GP Controller talks to the PCM and throw codes whenever it has a problem, so you best approach there would be to scan it with a good scan tool. You might be able to pull the GP harness off and monitor the GP pins on the harness (front two and back two) for voltage at first Key On similar to the GPR testing. I think the GP controller contains a series of solid state relays, one for each GP.

Sorry, don't have any direct experience with those animals.
 

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[ QUOTE ]
To check Glow Plugs.
· Remove the electrical connector on the inboard side of valve cover at the gasket.

[/ QUOTE ]

Ok, I probably picked the worst day to try to do this because it is COLD here. How in the #[email protected]% do you get the connector off? I was not able to get it off and was afraid of breaking it.
 

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Discussion Starter #14
They are tough little buggers, and hard to get to.

Push down on the lump on the center of the connector to release the hooks just to each side of that lump and at the same time use a small screwdriver to gently pry the connector apart at each end. Stick the screwdriver in at the joint where the seal is and twist.

Hope that helps. I'll be getting at mine in the next couple of days and will try to post a picture.
 

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[ QUOTE ]
They are tough little buggers, and hard to get to.

Push down on the lump on the center of the connector to release the hooks just to each side of that lump and at the same time use a small screwdriver to gently pry the connector apart at each end. Stick the screwdriver in at the joint where the seal is and twist.

Hope that helps. I'll be getting at mine in the next couple of days and will try to post a picture.

[/ QUOTE ]

Mine was being difficult to get off, but I discovered I could just stick the multimeter's probe in next to the wire to get a reading, without unplugging the connector.
 

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You can just take your multimeter put the leads in the top of the connector. You don't even have to take the plug off.
 

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Discussion Starter #17
[ QUOTE ]
You can just take your multimeter put the leads in the top of the connector. You don't even have to take the plug off.

[/ QUOTE ]

If you're talking about sticking the multimeter lead down beside the wire going through the seal, I think I'd avoid doing that. Those seals are there to keep moisture out of the connectors. If you damage a seal, you may find that the terminals will get corroded, causing at best a bad connection, and at worst a toasted external connector.

I've been trying to find a source for the external connector, but haven't been successful. About the only other way to repair that is a $500 engine harness. /ubbthreads/images/graemlins/eek.gif
 

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[ QUOTE ]
You can just take your multimeter put the leads in the top of the connector. You don't even have to take the plug off.

[/ QUOTE ]
I don't think that works anyway. All the leads come back to a common point so it won't really tell you anything unless all the plugs were bad.
 

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Discussion Starter #19
[ QUOTE ]
[ QUOTE ]
You can just take your multimeter put the leads in the top of the connector. You don't even have to take the plug off.

[/ QUOTE ]
I don't think that works anyway. All the leads come back to a common point so it won't really tell you anything unless all the plugs were bad.

[/ QUOTE ]

Exactly right, I forgot about that. /ubbthreads/images/graemlins/crazy.gif

OTC makes a tool that's a connector with each wire brought out to a test point to check GP's and injectors, but they want $75 for it. Pulling the connector is much cheaper and works just as well.
 

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Great write up! One quick comment, when my GPR went bad, it was intermittent.
I would turn the key on, wait to start, and try to start it. at first, once out of 10 times it wouldn't start right up, and I'd repeat the process.
Eventually, it wouldn't start no matter what.

Only reason I mention this, is using your great testing techniques, you might "luck in" and test it when it was working.
The 99 and up GPR is like 25 bucks at the local parts store, and the local parts store DOES stock them, and it takes under an hour to replace it.

Hint hint.

When in doubt, change it.
 
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