Verify Glow Plud Test
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
Verify Glow Plud Test
I just want to verify my diagnosis of bad glow plugs. This is a 2000 F250, build date 8/99. Cold start problems, relay is fine, have two and both pass power when PCM demands it and cycle off after 1.5 to 2 minutes when cold. I disconnected the left valve cover plug and checked the two outer connectors on each end with a trouble light. Both outside pins lit the light while both of the adjacent inside pins did not light up. I thought it odd that both inside glow plugs would test bad but this would explain mt problem.
Is this test valid? I don't want to order expensive unnecessary parts?
Lewis
Is this test valid? I don't want to order expensive unnecessary parts?
Lewis
Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,112
From: Rio Rico, AZ.
I just want to verify my diagnosis of bad glow plugs. This is a 2000 F250, build date 8/99. Cold start problems, relay is fine, have two and both pass power when PCM demands it and cycle off after 1.5 to 2 minutes when cold. I disconnected the left valve cover plug and checked the two outer connectors on each end with a trouble light. Both outside pins lit the light while both of the adjacent inside pins did not light up. I thought it odd that both inside glow plugs would test bad but this would explain mt problem.
Is this test valid? I don't want to order expensive unnecessary parts?
Lewis
Is this test valid? I don't want to order expensive unnecessary parts?
Lewis
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
The voltage is identical on both posts when the relay is activated, just tested it and was 11.67volts on both. The resistance on both outer pins is .8 ohms, the adjacent inside pins are both open. My main question is are the outer 4 pins on the connector each hooked to a glow plug? It that's the case I've got two on that bank that are burned out. I know on the earlier model 7.3 they only had two pins on the connector for each bank and I don't know when they changed to 4 Glow plug pins per bank. I assume mine has the 4 pin set up because the wiring on the harness side has larger wire and connectors on the outer 4 on the plug.
It's a Van Gogh
Joined: Feb 2010
Posts: 7,802
Likes: 1,333
From: Elk Grove, CA
A quick cheap test is monitor voltage from your cigar lighter. Typically the voltage will drop close to a full volt when the GPs are energized. You'll see the voltage pop up that 1 volt when the GPs turn off. Stand to reason if the voltage only pops up say half a volt that would indicate some GPs not working.
Which is the type of loosey goosey diagnostics that works for me, and mostly makes other people laugh.
But I'll attach a diagram for ya.
If you buy GPs get them from Riff Raff or some other reliable place. There are counterfeits out there.
Which is the type of loosey goosey diagnostics that works for me, and mostly makes other people laugh.
But I'll attach a diagram for ya.
If you buy GPs get them from Riff Raff or some other reliable place. There are counterfeits out there.
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
Thanks for the diagram, it looks like the outer 2 pins on each plug carry high voltage to the glow plugs. My battery voltage drop with the relay engaged is ~3/4 of a volt. Unfortunately the plug circuit from the valve cover plug on test open for 50% of the left bank. I'm too lazy to remove all the goodies for the right bank to test the resistance so I'll assume at least one of them is bad. Looks like RiffRaff will get some more business, I'll be replacing all the glow plugs, under cover harness, and valve gaskets just to be safe, pretty sure these are 23 year old original parts.
I hope I don't need it but does anybody have any tips or tricks for removing stuck Glow plugs?
Lewis
I hope I don't need it but does anybody have any tips or tricks for removing stuck Glow plugs?
Lewis
Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,112
From: Rio Rico, AZ.
In the 40 years that I was a tech, I've only had one glow plug sieze up. Not really a life threatening situation, you just have one cylinder that won't ignite on a cold winter day's start. Once it's running on the other seven, it will heat up and start firing within minutes or even seconds, depending on conditions. Sometimes it's better to just leave it in, lot's of work to get it out, up to and sometimes including removing the cylinder head to get after it.
Logistics Pro
Joined: May 2017
Posts: 4,667
Likes: 1,455
From: Muskogee, Ok
Hopefully they aren't stuck.
They get torqued to 14 foot pounds.
They require a 10mm deep well 1/4" drive socket. A 3/8" drive will be too wide to fit between the rocker.
Use a piece of 3/16" vacuum tube about 6" long to retrieve them once they are loose, and also to thread in the new ones. The tubing will shove over the end of the glow plugs. That or use chopsticks, your fingers won't fit
They get torqued to 14 foot pounds.
They require a 10mm deep well 1/4" drive socket. A 3/8" drive will be too wide to fit between the rocker.
Use a piece of 3/16" vacuum tube about 6" long to retrieve them once they are loose, and also to thread in the new ones. The tubing will shove over the end of the glow plugs. That or use chopsticks, your fingers won't fit
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Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,112
From: Rio Rico, AZ.
Yes, a 1/4" drive socket is a must have with this job. The shoulder of the 3/8" drive will jam itself against the push rod and make a cross threading scenario for the glow plug.
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Thanks for the diagram, it looks like the outer 2 pins on each plug carry high voltage to the glow plugs. My battery voltage drop with the relay engaged is ~3/4 of a volt. Unfortunately the plug circuit from the valve cover plug on test open for 50% of the left bank. I'm too lazy to remove all the goodies for the right bank to test the resistance so I'll assume at least one of them is bad. Looks like RiffRaff will get some more business, I'll be replacing all the glow plugs, under cover harness, and valve gaskets just to be safe, pretty sure these are 23 year old original parts.
I hope I don't need it but does anybody have any tips or tricks for removing stuck Glow plugs?
Lewis
I hope I don't need it but does anybody have any tips or tricks for removing stuck Glow plugs?
Lewis
The plugs when new are supposed to be around .5 or .6 Ohms. Yes each of the two outer pins (the larger ones) on the 9-pin connecters at the valve cover gaskets are for an individual glow plug. I think ohm testing them at the 42-pin connector is a good way to troubleshoot the plug and it's nearby wiring, but hooking up a test light to the + battery terminal and probing the outer pins on the valve cover gasket will show if the plug is either dead or the UVCH wiring is a problem. If all 8 of them light up at the valve cover gasket pins and your relay tests good then probably everything is okay. There would have to be wiring issues somewhere between those two points for any of them to still not work with the relay energized.
Taking them out with the motor warm I have heard is a good trick to avoid having any get stuck in there.
5th Wheeling
Joined: Aug 2023
Posts: 40
Likes: 15
From: Colorado
Yes sounds like your relay is fine. In my experience a minimal voltage drop of .1 or .2 volts across the relay is normal with it energized. 0 would be ideal but is always some loss. A dead one wont even light up a test light on one side.
The plugs when new are supposed to be around .5 or .6 Ohms. Yes each of the two outer pins (the larger ones) on the 9-pin connecters at the valve cover gaskets are for an individual glow plug. I think ohm testing them at the 42-pin connector is a good way to troubleshoot the plug and it's nearby wiring, but hooking up a test light to the + battery terminal and probing the outer pins on the valve cover gasket will show if the plug is either dead or the UVCH wiring is a problem. If all 8 of them light up at the valve cover gasket pins and your relay tests good then probably everything is okay. There would have to be wiring issues somewhere between those two points for any of them to still not work with the relay energized.
https://www.youtube.com/watch?v=WeVeCvQgolw
https://www.youtube.com/watch?v=oywYccXgZHE
Taking them out with the motor warm I have heard is a good trick to avoid having any get stuck in there.
The plugs when new are supposed to be around .5 or .6 Ohms. Yes each of the two outer pins (the larger ones) on the 9-pin connecters at the valve cover gaskets are for an individual glow plug. I think ohm testing them at the 42-pin connector is a good way to troubleshoot the plug and it's nearby wiring, but hooking up a test light to the + battery terminal and probing the outer pins on the valve cover gasket will show if the plug is either dead or the UVCH wiring is a problem. If all 8 of them light up at the valve cover gasket pins and your relay tests good then probably everything is okay. There would have to be wiring issues somewhere between those two points for any of them to still not work with the relay energized.
https://www.youtube.com/watch?v=WeVeCvQgolw
https://www.youtube.com/watch?v=oywYccXgZHE
Taking them out with the motor warm I have heard is a good trick to avoid having any get stuck in there.
Injector resistance can be checked all the way back at the IDM
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
I appreciated the help. According to all my tests the fault lies under the valve covers. I should have the glow plugs, under cover harness, and gasket tomorrow from RiffRaff and will start on it then. Deer season just opened and I don't want to get stuck 40 miles away with a no start problem, It's not too bad here on the ranch where I can always tow it back with a tractor if need be. My worry at this point is a stuck plug or a build up on the glow plug tips that would make removal difficult or impossible. We'll see shortly, keep your fingers crossed.
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