glow plug issues
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New User
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glow plug issues
So i have a 99 f-250 XLT Super Duty with the 7.3L Powerstroke. Its been a pain to start in the cold morning here in nevada and ive had a glow plug issue for quite a while just tired of putting money into it only to have the same problem reoccur so im coming to the internet for help. Had a fuel knock awhile back in cylinder 8 (driver side rear so im told) and was told glow plugs were bad, so i had them changed and everything cleared up for awhile. then i stopped driving the truck for awhile because of the outrageous fuel prices. When i went last november to use it as my daily again, it wouldnt start in the mornings unless it was plugged in or sprayed a ton of starting fluid into the airbox. I heard from a friend that the harness itself is known to go bad and basically grounds the wiring out causing the glow plugs not to activate. Ive also read on here that the relay is known to go out in them. Not sure what to do, any help would be appreciated
Cargo Master
Joined: May 2010
Posts: 3,047
Likes: 9
From: Snohomish, WA
Check out My Glowplug System Page There is the information you need along with a couple videos showing how to perform basic checks.
Cargo Master
Joined: Aug 2009
Posts: 2,137
Likes: 13
From: Glendive, MT
Welcome aboard!
I check my starting system every year about this time just to make sure it is ready for winter. I start by load testing the batteries. Then on to your issue. There is a nine pin connector in each valve cover. Pull that connector and ohm the pins. They are as follows:
Glow Plug
Glow Plug
Injector
Injector
Injector Common
Injector
Injector
Glow Plug
Glow Plug
Glow Plug to ground should ohm out between .7 and 1.0 ohms. A reading of 0 indicates a shorted plug or wire under the valve cover (very rare). A high reading indicates a poor connection under the valve cover.
Injector to common should be approx 3-5 ohms or close to that. They should all be close to even.
Then plug the connectors back in and check voltage drop across the glow pulg relay. With the engine off and cold you should have battery voltage across the 2 large poles of the relay. Have a helper turn the key on but do not start. The voltage across the two large poles should drop to less than 1 volt. If it is higher, the contacts inside the relay are getting bad and the relay needs to be replaced.
I check my starting system every year about this time just to make sure it is ready for winter. I start by load testing the batteries. Then on to your issue. There is a nine pin connector in each valve cover. Pull that connector and ohm the pins. They are as follows:
Glow Plug
Glow Plug
Injector
Injector
Injector Common
Injector
Injector
Glow Plug
Glow Plug
Glow Plug to ground should ohm out between .7 and 1.0 ohms. A reading of 0 indicates a shorted plug or wire under the valve cover (very rare). A high reading indicates a poor connection under the valve cover.
Injector to common should be approx 3-5 ohms or close to that. They should all be close to even.
Then plug the connectors back in and check voltage drop across the glow pulg relay. With the engine off and cold you should have battery voltage across the 2 large poles of the relay. Have a helper turn the key on but do not start. The voltage across the two large poles should drop to less than 1 volt. If it is higher, the contacts inside the relay are getting bad and the relay needs to be replaced.
Lead Driver
Joined: Sep 2005
Posts: 9,399
Likes: 188
From: Norco,CA
I had that problem in my 99 f350 and it was the relay. It would click but didn't have the volts to the glow plugs. There cheap, give it a try. I could tell you how to check it but just replace it. If the glow plugs are new, and motorcraft, not AC plugs you should be fine.
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New User
Joined: Oct 2014
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Alright I'll test it Sunday since I work tomorrow but if the glow plugs are bad and pulling the too many amps across them won't the pcm tell the relay not to engage? Not to familiar with the computer stuff. This is the newest vehicle I've ever owned. Most of my other trucks are late 70s early 80s
i ain't rite
Joined: Mar 2005
Posts: 65,446
Likes: 5,517
From: Marlboro Mental Hospital.
first thing i would do is test the relay. it can be bad and the in dash indicator will still come on.
then when you change the relay put a small light or led in the dash hooked up to the relay output to show you if the relay is actually working.
then when you change the relay put a small light or led in the dash hooked up to the relay output to show you if the relay is actually working.
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I understand starting fluud is awful for the motor. I've rebuilt plenty of CAT engines that have had cans of starting fluid sprayed into them. But when it's either a shot of starting fluid or my job im choosing the fluid dude. What I was getting at is if the pcm is reading that the glow plugs are pulling to many amps across them won't the pcm keep the relay from engaging to protect the engine?
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Lead Driver
Joined: Jun 2004
Posts: 6,311
Likes: 578
From: Amarillo, TEXAS!
No. It will not. IF it's a CA emissions engine, it would set the MIL, and that's about it. On a glow plug-equipped engine, ether goes beyond just being bad for the engine. It can cause a new window to be installed in the engine block. If you must use it, disable the glow plug system entirely first.
Elder User
Joined: Sep 2011
Posts: 979
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From: Vancouver
No. It will not. IF it's a CA emissions engine, it would set the MIL, and that's about it. On a glow plug-equipped engine, ether goes beyond just being bad for the engine. It can cause a new window to be installed in the engine block. If you must use it, disable the glow plug system entirely first.
If you see one of the terminals on the glow plug relay looking black or overheated, replace the relay whether it tests okay or not.
Larry
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Tested the relay last night after work and I got 0v on the right side of the relay so I went and got a new relay today ($55 @ AutoZone, the only parts store that stocks them) and installed it. When the key is on I can actually hear the relay buzzing unlike the old one. Thanks for the help everyone the real test comes tomorrow, weather man says it's supposed to be about 40 degrees tomorrow morning so I'll give it a test
Lead Driver
Joined: Jun 2007
Posts: 7,760
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From: Hampton, Maryland.
Turn the key forward and let it sit like that for 30-45 secs before trying to start. The WTS light is basically an idiot light and is not an indicator of how long the GP's stay energized. They can stay on for 90 seconds or more in certain situations. Let them get heat in the cylinder for a little while, if the relay was the fix, she'll start much easier with that extra time for the GP's to work.
i ain't rite
Joined: Mar 2005
Posts: 65,446
Likes: 5,517
From: Marlboro Mental Hospital.
Turn the key forward and let it sit like that for 30-45 secs before trying to start. The WTS light is basically an idiot light and is not an indicator of how long the GP's stay energized. They can stay on for 90 seconds or more in certain situations. Let them get heat in the cylinder for a little while, if the relay was the fix, she'll start much easier with that extra time for the GP's to work.
Lead Driver
Joined: Jun 2007
Posts: 7,760
Likes: 27
From: Hampton, Maryland.
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