How to know
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Lead Driver
Joined: Jun 2006
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From: Near Yosemite CA
How to know
I am going to work on a 95 F-350 PSD with 311k on her, the glow plugs (system) does not work, if not plugged in has a REALLY hard time starting... where do I start to figure out what isn't doing its job? What is common, GPR, timer, or glow plugs going out. Wait to start light comes on,,,, if that means anything.
Senior User
Joined: Nov 2000
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From: Drayton, ND
I would lean towards the GPR. With the hood up, drivers door open, radio and fan off, you should hear it click when you turn the key on. The GPR click indicates that it is allowing 12 volts to the glow plugs. You should be able to take measurements to show that it is outputting 12 volts for sure. The glow plugs themselves are checked easiest by measuring their resistance.
Mine has one bad gp, but will still start at 10F, without much trouble, confirmed the other day. I do like to leave the key on for awhile after the "wait to start" light goes out.
Mine has one bad gp, but will still start at 10F, without much trouble, confirmed the other day. I do like to leave the key on for awhile after the "wait to start" light goes out.
Post Fiend
Joined: Apr 2004
Posts: 12,835
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From: Silver Lake Dunes, MI
yep what travis said. use a test light to check glow plug relay. it should have power on both large terminals when the truck is cold and the key is first turned on. If that tests good then use an ohm meter to test the glowplugs from the valve cover plugs(5 pins on each connector, 2 connector per valve cover, the outside terminals on each side are the glow plug terminal) Hook ground side of ohm meter to battery ground and touch positive lead to connector pins. should be 3 ohms or less. 1 ohm is ideal
FTE Leadership Emeritus
Joined: May 2001
Posts: 13,653
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From: Cabot, Arkansas
With 311,000 miles I wouldn't bother testing anything. Replace the relay and the plugs and be done with it.
The WTS light working means the PCM is sending it's signal, so in effect the "timer" is good.
The WTS light working means the PCM is sending it's signal, so in effect the "timer" is good.
Fleet Mechanic
Joined: Oct 2003
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From: CentralEastern Utah
Plugs are +/- 10 bucks each. Make sure you get motorcraft beru plugs. Do not get autolites. Changing them is'nt too bad. Hardest part is pulling the valve covers.
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Fleet Mechanic
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Senior User
Joined: Nov 2000
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From: Drayton, ND
Somebody has to play devil's advocate, but it's entirely possible that some of those parts may have been changed not too long ago. Plus, the benefit of troubleshooting and identifying the broken part is a bonus, for those who have not done it before.
Posting Guru
Joined: Nov 2006
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From: Herndon KY
I am with cookie, the peace of mind of having brand new stuff is worth the 120 bucks. Also IMO if you don't know when your GP's were changed last you need to change them now!! There are way to many guys that are breaking those things off, all it takes is one to have to much carbon and you are in for a lot of work and expense.
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