Glow Plugs
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New User
Joined: Feb 2012
Posts: 24
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From: Cleveland, AL
Glow Plugs
I need some help with glow plugs. My 1987 F-250 6.9l cranks great with the warmer plugged in but will not start if I dont plug it in. The "wait to start" light seems to be working fine except for the few times that it has come on or blinked on while I was driving.
So far, I have done the following:
1. Replaced the glow plug relay.
2. Bypassed the connector with the two hot leads that lead to the relay.
3. Tested the glowplugs for continuity using the "resistance alarm"
4. Tested the glowplugs by attatching the red lead to the positive side of battery and touching each glow plug tip which gave me 12.59 volts on all.
5. Ran a new ground wire from the neg of battery to the block where the the black ground wire from the relay controller is landed.
Voltage:
I have 12.59 volts to the LINE side of the relay.
The ingition is bringing the proper voltage to the relay.
I am reading about 6 volts on the load side of the relay constantly when the key comes on. The voltage is not dropping.
I am also reading 6 volts on the connector to the glow plugs.
Still no starting without plugging in. Any more advice??
So far, I have done the following:
1. Replaced the glow plug relay.
2. Bypassed the connector with the two hot leads that lead to the relay.
3. Tested the glowplugs for continuity using the "resistance alarm"
4. Tested the glowplugs by attatching the red lead to the positive side of battery and touching each glow plug tip which gave me 12.59 volts on all.
5. Ran a new ground wire from the neg of battery to the block where the the black ground wire from the relay controller is landed.
Voltage:
I have 12.59 volts to the LINE side of the relay.
The ingition is bringing the proper voltage to the relay.
I am reading about 6 volts on the load side of the relay constantly when the key comes on. The voltage is not dropping.
I am also reading 6 volts on the connector to the glow plugs.
Still no starting without plugging in. Any more advice??
Lead Driver
Joined: Mar 2006
Posts: 5,098
Likes: 1,504
From: western SD
How long does the WTS light come on when you first turn the key? I should burn for up to 15 sec. with the new style controler, depending on temps. Have you checked to make sure all the GPs are good? One bad GP can cause a shorter warm up of the GPs.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
Likes: 4
From: 8600 ft in Colo
You've got 6v on the load side of the relay anytime the key is on? Even after the controller stops cycling the plugs? What voltage in on the power supply side? Disconnect the white wire from the controller to the relay, and see if there's still voltage on the load side with the key on.
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New User
Joined: Feb 2012
Posts: 24
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From: Cleveland, AL
PHY:
Im getting 12.59 volts on the hot side of the relay. Without the white wire attatched, I am still getting between 5.6 to 6.2 volts.
I am only getting power to the ingition side (small post with red wires) when the key is on which is correct and the relay is only transferring power when the key is on, but the voltage is constant on the relay side when the key is on.
Im getting 12.59 volts on the hot side of the relay. Without the white wire attatched, I am still getting between 5.6 to 6.2 volts.
I am only getting power to the ingition side (small post with red wires) when the key is on which is correct and the relay is only transferring power when the key is on, but the voltage is constant on the relay side when the key is on.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
Likes: 4
From: 8600 ft in Colo
Disconnect the glow plug wires from the z-bracket & see if the 6v is coming from the relay or the wires. It's probably from the relay, but there could be some shorted wiring...
Assuming it's coming from the relay, and the white wire is disconnected from the relay, then the relay is bad...
Assuming it's coming from the relay, and the white wire is disconnected from the relay, then the relay is bad...
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New User
Joined: Feb 2012
Posts: 24
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From: Cleveland, AL
Farmert:
Thanks for replying. The glow plugs appear to be fine. I checked them two different ways listed in the original post #'s 4 and 5. Do you know of another test I can do?
Thanks for replying. The glow plugs appear to be fine. I checked them two different ways listed in the original post #'s 4 and 5. Do you know of another test I can do?
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Methanoholic
Joined: Mar 2009
Posts: 6,442
Likes: 8
From: Maine (NorCal Native)
A Ohm meter is the only way to ensure the GP's are good ... The tests you have performed are suspect to miss diagnosis and should only be used for a preliminary test.
They should Ohm out between .5 and 1.
However, I suspect the relay is bad ... Both large terminals should have close to 12v (maybe as low as 10v) for up to 15 seconds after the key is turned on, then it will cycle ...
Also this sporadic "Blink" of the WTS while driving is concerning!
Short in the wiring ...
-Enjoy
fh : )_~
They should Ohm out between .5 and 1.
However, I suspect the relay is bad ... Both large terminals should have close to 12v (maybe as low as 10v) for up to 15 seconds after the key is turned on, then it will cycle ...
Also this sporadic "Blink" of the WTS while driving is concerning!
Short in the wiring ...
-Enjoy
fh : )_~
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Your glow plugs and their electrical system should have nothing whatsoever to do with whether your engine "cranks" or not. Yes, they may well determine whether or not your engine starts in cold weather, but they should not determine whether or not it "cranks".
You have a wiring problem.
By the way, I don't trust any of the multimeters I own to accurately measure ohms in the range of 0.5 to 1 ohm. They're just not designed to do that. Best way to test glow plug operation would be to remove them & connect them to their designed voltage. Other methods only give second-hand info.
You have a wiring problem.
By the way, I don't trust any of the multimeters I own to accurately measure ohms in the range of 0.5 to 1 ohm. They're just not designed to do that. Best way to test glow plug operation would be to remove them & connect them to their designed voltage. Other methods only give second-hand info.
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New User
Joined: Feb 2012
Posts: 24
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From: Cleveland, AL
ARTFD:
Are you saying that the glow plug system has nothing to do with heating the block and starting (cranking) the engine in cold weather?
I have read many threads on here that state differently. Plus my voltage readings and electrical experience are also pointing to glow plug issues. Do you know of any other reasons my truck starts (cranks) fine with the warmer pluged in, but will not crank with the engine cold?
Are you saying that the glow plug system has nothing to do with heating the block and starting (cranking) the engine in cold weather?
I have read many threads on here that state differently. Plus my voltage readings and electrical experience are also pointing to glow plug issues. Do you know of any other reasons my truck starts (cranks) fine with the warmer pluged in, but will not crank with the engine cold?
Methanoholic
Joined: Mar 2009
Posts: 6,442
Likes: 8
From: Maine (NorCal Native)
I believe there is some confusion over your use of "cranks" ...
Typically the term "Cranks" means the motor turns over with the starter.
It appears you use the term "Cranks" for the typical term "Starts".
-Enjoy
fh : )_~
Typically the term "Cranks" means the motor turns over with the starter.
It appears you use the term "Cranks" for the typical term "Starts".
-Enjoy
fh : )_~
