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The Oracle
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343 Posts
Discussion Starter #1
how do i go about checking it to see if its still good...gonna be doing the plugs soon and wanted to check that so i could replace it at the same time if needed....


thanks again guys
 

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TDG MAFIA MEMBER #77
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940 Posts
I would check the GPR before diving into the plugs. You can get a new GPR 109 at NAPA for around $30 -40.

These are instructions for 99-03 7.3 PSD's. The differences between the 94-94 and the 99-03 are noted at the bottom in blue.

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.
· Locate the GPR – Its 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 one of the large posts.
· 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.

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.
· 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.



The difference is the relay on the 94-97 PSD's will be on the passenger side valve cover.

Your truck will have 2 connectors per valve cover instead of one, so the glow plugs will be the outer wires on each plug (2 wires per connecter)



Good luck!
 

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When your turn the key on to start the glow plugs, does the volt gauge peg to the left and then return to the middle after a few seconds. If so, the GPR is working fine. I just changed my plugs and she lit fin in 10 degree temps.
 

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Senior Member
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TooLoudTooBad said:
I would check the GPR before diving into the plugs. You can get a new GPR 109 at NAPA for around $30 -40.

These are instructions for 99-03 7.3 PSD's. The differences between the 94-94 and the 99-03 are noted at the bottom in blue.

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.
· Locate the GPR – Its 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 one of the large posts.
· 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.

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.
· 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.



The difference is the relay on the 94-97 PSD's will be on the passenger side valve cover.

Your truck will have 2 connectors per valve cover instead of one, so the glow plugs will be the outer wires on each plug (2 wires per connecter)



Good luck!
Nice write up :Thumbup:

The only thing I didn't see is that you sould check the voltage of both large terminals on the GPR while the glow plugs are running. If the voltage reading differs more than 1 Volt then your relay is getting old and has some resistance in the contacts and is using up some of the voltage that could be sent to the plugs.
Typically you will see a .3 ot .5 volt difference between the two terminals.
 

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The Oracle
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Discussion Starter #5
i'll probably just replace it too....might as well

im gonna be in there doing injector orings, thats why im doing the glow plugs too.....(and harnesses)
 

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TDG MAFIA MEMBER #77
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Good idea!

I guess I would change them out too if I was already in there. What injectors are you putting in?
 

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Thats what I did. Went to stage 1 injectors, new glow plugs and new relay while I was doing it.

Check out rockauto.com They have AC Delco glow plugs for 8 bucks each IIRC.
 

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The Oracle
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343 Posts
Discussion Starter #8
no new injectors....just doing the o-rings
 

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TDG MAFIA MEMBER #77
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AutoZone might still carry the MotorCraft glow plugs. About $10.00 each a few years ago.
 

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The Oracle
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343 Posts
Discussion Starter #10
i got some autolites from NAPA for $10 each
 

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Member
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a guy i work with has a 2003 7.3 with 200,000 miles on it and when its about low 30's into the 20's it will crank but not start could the GPR be the problem ? how often should you change the glow plugs??
 

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youngPSD said:
a guy i work with has a 2003 7.3 with 200,000 miles on it and when its about low 30's into the 20's it will crank but not start could the GPR be the problem ? how often should you change the glow plugs??
Definitly check the GPR as described in a previous post. You could have an issue with a GP but I would cover all bases first - check battery voltage at that temp, and ohm check the GP at the valve cover gasket harness (also explained earlier). If everything comes out good there post up again and I can get a spec on the amp draw that the GP should be using while they are opperating (cant remember exactly right now).
 

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Senior Member
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youngPSD said:
a guy i work with has a 2003 7.3 with 200,000 miles on it and when its about low 30's into the 20's it will crank but not start could the GPR be the problem ? how often should you change the glow plugs??
Definitly check the GPR as described in a previous post. You could have an issue with a GP but I would cover all bases first - check battery voltage at 10-20 deg. (bad batteries possibly), and ohm check the GP at the valve cover gasket harness (also explained earlier). If everything comes out good there post up again and I can get a spec on the amp draw that the GP should be using while they are opperating (cant remember exactly right now).
 
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