Glow plugs not turning on . - Diesel Forum - TheDieselStop.com
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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 10-28-2006, 02:33 PM   #1 (permalink)
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Glow plugs not turning on .

Over the last couple weeks I have been having a hard start problems.
Normally after it sits over night , but not always.

I have noticed that when it starts without problems, when I turn the key to the on pos. the voltage gets yanked down some by the glowplugs being on.

When it wont start, the voltage never pulls down. It will crank with no problems put never fire. Today I put a jumper on one of the glow plug relays and watched the voltage. It pulled down as I acspected.
I tried to start it and it fired a couple time but it wasnt having it cuz the other bank of the motor didnt have the glow plugs on a I assume.

Could someone tell me what controls the GP relays.
Or, is there any advice on where I should start.
Ive gave up and come back 5 min. later just to try it and they start working again and it fires up with no problem.
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Old 10-28-2006, 06:48 PM   #2 (permalink)
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Re: Glow plugs not turning on .

Welcome to TheDieselStop [img]/ubbthreads/images/graemlins/smile.gif[/img]

Check Here for the scoop on the glow plug system.

There's only one Glow Plug Relay, so if you jumpered the right one, all your GP's should have worked, not just one bank.

The relay toward the front is the Intake Air Heater relay, and would also cause the voltage to pull down. It heats the intake air for extended idling in cold conditions, but not for starting. If you heated it up with your jumper, it would help starting, but not nearly as effective as the glow plugs.

Your GPR probably has bad contacts and works intermittently if it started OK 5 minutes later.
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Old 10-28-2006, 07:51 PM   #3 (permalink)
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Re: Glow plugs not turning on .

thanks for the reply and the link. Very helpfull.
I went to my buddies shop and printed off schematics and troubleshooting info for the GP circuit. Im glad you stated which relay is the GP relay cuz the pictures and schematics just say "top right of engine". That dont help when they are next to each other on the same side of the engine.
I learned the computer feeds power to the GP relay activation circuit and then the GP controller grounds the GP relay activation circuit.
Pretty goofy.

I will be playin with it tommorow.

Again, thanks for the info.
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Old 10-28-2006, 08:24 PM   #4 (permalink)
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Re: Glow plugs not turning on .

[ QUOTE ]
I learned the computer feeds power to the GP relay activation circuit and then the GP controller grounds the GP relay activation circuit.
Pretty goofy.

[/ QUOTE ]

Not really that goofy, The control circuit of the GPR is fed power thru a key-on hot circuit, and the circuit is completed (to ground) by an electronic switch in the PCM. That's what pulls in the relay.

The GP controller only exists on some California trucks and most (all?) Excursions, and if you have a GP controller, then you won't have a GPR.

Glad I could help out.
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First truck -- 1929 Model A Ford pickup, restored from ground up. Wish I still had it!
99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version), AIS, coolant filter w/"hokum" bracket, regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.

Hard or no-start? Check Here
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