"cycling" glow plugs
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Mountain Pass
Joined: Jun 2004
Posts: 169
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"cycling" glow plugs
I have heard conflicting stories, is it effective to keep recycling or is it a waste? I could not plug my truck in last night as usual because the block heater was shorting out, I knew id suffer for it in the AM and i am. Thanks
Laughing Gas
Joined: Feb 2006
Posts: 947
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I don't know for sure but i have heard from a couple of people and read on this forum that you can leave the key in the run position for about 30 seconds, turn to the off position for about 30 secs, and then to the run for another 30 secs and then start.
Senior User
Joined: Oct 2004
Posts: 160
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From: King George, Virginia
From what I’ve read in the Factory Manual, the GPR cycles and does not just click on. You’ll hear a buzzing sound when it’s cold out. This buzzing sound of the GPR cycling will continue after the WTS light goes off. If the buzzing stops and you want some more Glow Plug action before starting, cycle the key and the GPR will start buzzing again. I find only one cycling is fine to start the truck, it was in the 20’s last night here. I can hear the buzzing in the truck. Hope this helps.
Senior User
Joined: Oct 2004
Posts: 376
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From: South Dakota
THis is out of the manual: Note Wait to Start "On" time (1-10sec.) is independent from Glow Plug Relay "On" time( up to 120 sec.) The Glow Plug (GP) light signal controls the WAIT TO START indicator light located on the instrument panel. When the light goes off, the engine is ready to be started. As a bulb check, the light comes on every time a key on reset occurs, even though the glow plug system is not commanded on. On-time normally varies between 1 and 10 seconds. WAIT TO START light on-time is independent of glow plug relay on-time because the glow plugs may stay on to improve performance until engine reaches operating temperature. I used to cycle the system, now I just wait for about 30 secs, unless it is really cold then I wait a little longer, and it has been starting fine.
Post Fiend
Joined: Feb 2006
Posts: 11,892
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From: Middle Tennessee
Originally Posted by nodakford
now I just wait for about 30 secs, unless it is really cold then I wait a little longer, and it has been starting fine.
Senior User
Joined: Oct 2004
Posts: 160
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From: King George, Virginia
The glow plugs do stay on longer than the WTS light, depending on the temperature. The cycling I was talking about was the square wave signal to the relay that causes it to buzz. The glow plugs come on for up to 120 seconds through rapid pulses of 12VDC to the relay. I can hear this in the cab if it’s cold out.
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Posting Guru
Joined: Jan 2006
Posts: 1,605
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From: Elkhorn, WI
you shouldnt have to cycle them at all. my truck started at 5 below zero with the key on for about 30 seconds and not plugged in. you might have a relay or some plugs going bad. i have never had to cycle my plugs more than once and thats with 210k on the engine and it gets cold up here in wisconsin
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Lead Driver
Joined: Oct 2004
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From: Columbia, MO
They turn on and stay on, for up to 120 seconds at first start. They don't "cycle" on and off. Have you ever started your truck with the door open, and notice that after a little while the lights suddenly get brighter? The GPR just turned off. But you never notice the lights go back dim, right?
The buzzing sound you hear is one of two pumps running - either the vaccum pump or the fuel pump. They will both run for a little while when you first start the truck, but shut off after about 30 seconds.
My theory on really cold starts is this, turn key on wait about 15 seconds, and start the truck. If your GP system is working ok, and your fuel is good, that should be all you need. It was about 7 degrees outside last night when I did this, and the truck started just fine. I had not had the block heater plugged in at all, and the truck had been sitting for the last 3-4 days without being run, temps all afternoon were in the teens. The truck was definately cold. Oh, and since my stock fuel bowl is gone, I also no longer have a fuel heater.
The buzzing sound you hear is one of two pumps running - either the vaccum pump or the fuel pump. They will both run for a little while when you first start the truck, but shut off after about 30 seconds.
My theory on really cold starts is this, turn key on wait about 15 seconds, and start the truck. If your GP system is working ok, and your fuel is good, that should be all you need. It was about 7 degrees outside last night when I did this, and the truck started just fine. I had not had the block heater plugged in at all, and the truck had been sitting for the last 3-4 days without being run, temps all afternoon were in the teens. The truck was definately cold. Oh, and since my stock fuel bowl is gone, I also no longer have a fuel heater.
Senior User
Joined: Oct 2004
Posts: 160
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From: King George, Virginia
I stand corrected. “Relay Cycling” After consulting the Hanes and Ford Factory Manual, it describes a “timed pulse function” for glow plug operation and these timed pulses can last up to 120 seconds depending on barometric pressure and oil temperature. The PCM determines how long the timed pulses are sent to the relay. Hanes has a warning “Operation of the glow plug system is completely automatic. Never bypass the timed pulse function of the glow plug system. A constant 12VDC will cause the glow plugs to overheat and fail”. I’m still not sure if they are considering a (up to) 120 second period a timed pulse or if the relay receives multiple short duration pulses during the glow plug on period. I do know when it’s really cold I hear a buzzing under the hood, I just figured from reading the tech pubs it was the GPR but I guess it could be the vacuum pump.
Postmaster
Joined: Jun 2005
Posts: 3,438
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From: New Hampshire
Wrong info?
Originally Posted by ponch37300
I don't know for sure but i have heard from a couple of people and read on this forum that you can leave the key in the run position for about 30 seconds, turn to the off position for about 30 secs, and then to the run for another 30 secs and then start.
Sorry but i may have passed on some faulty info i got on the forum last year at this time on cold starts and cycling the glow plugs. Turned out i had a weak GPR and by cycling it 2 or 3 times it seemed to help with quick cold weather starts. I've since replaced my GPR but kept the habit of cycling the GP's a few times. I'm going to follow JT's advice on the 15 second wait and try her then. Glad this issue came up and sorry if i passed on some wrong info(even though i get effective immediate starts). Nut
