Intermittent Glow Plug cycle
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Senior User
Joined: May 2008
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From: Bentonville, AR
Intermittent Glow Plug cycle
Why does my glow plug come on for about 3 seconds and go off...about once a minute.
I turn on the key.
Glow plug light goes out.
I crank the truck over...starts like a champ.
While sitting there idling the glow plug light comes on, the lights dim from the electrical load and goes off after about 3 seconds.
I also did notice my temp guage is not registering yet.
Why is the glow plug intermittent.
Thanks,
Tim
I turn on the key.
Glow plug light goes out.
I crank the truck over...starts like a champ.
While sitting there idling the glow plug light comes on, the lights dim from the electrical load and goes off after about 3 seconds.
I also did notice my temp guage is not registering yet.
Why is the glow plug intermittent.
Thanks,
Tim
Senior User
Joined: Feb 2007
Posts: 119
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my '92 does the same thing. the guy i bought it from put a heavy duty push button switch inline with the glow plug relay so when you turn the key on you hit the switch, the g/p light lights up then goes off after 10 seconds then release the switch. i couldn't figure out why he did it. so i took the switch out and hooked the relay up like it should be. thats when i noticed the relay would come on sporratically. as the engine is running i can see the ammeter drop for a second or so whenever the relay comes on. i put the switch back in.
i assume it's a bad relay. the relay is something like $129 from oreilly. i haven't had the time or money to replace it. i plan to before it gets cold. in the summer time i don't need it once i've started the engine for the day.
if anyone has any other ideas i'm all ears. i'd hate to replace a good $130 relay.
i assume it's a bad relay. the relay is something like $129 from oreilly. i haven't had the time or money to replace it. i plan to before it gets cold. in the summer time i don't need it once i've started the engine for the day.
if anyone has any other ideas i'm all ears. i'd hate to replace a good $130 relay.
Junior User
Joined: Jan 2008
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From: portsmouth n.h.
well timcos the glow plug system can be hard if you dont understand how it works, turning the key to the on position, heats up the plugs red hot to heat the fuel to make it combust easier, after the truck starts, the glow plugs dont stay red hot once you let off the key and the engine starts, they cycle in order to keep the fuel warm, in the winter mine will cycle a few times intermitintly for a few seconds, then shut off, totally normal, if it doesnt start after the light goes out and repeted cycles of the plugs is nessary to start, then it could be plugs or maby the wire harness, the tips wich connect to the plugs seem to corrode up here in new hampshire
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for me the plugs come on and off indefinately. i drove all over town for an hour with the glow plugs cycling sporratically. there didn't seem to be a ryme or reason. i just put the bypass swith back in place and put it on the back burner.
part of me is thinking why did the previous owner pay a mechanic to run a bypass switch for the glow plug controller when the crontroller is only $130 from the auto parts store. part of me is thinking he replaced it and it wasn't the problem and rather than dump more money in an (at the time) eight or 9 year old truck he'd have them bypass the relay. but maybe at the time relays cost more than they do now.
part of me is thinking why did the previous owner pay a mechanic to run a bypass switch for the glow plug controller when the crontroller is only $130 from the auto parts store. part of me is thinking he replaced it and it wasn't the problem and rather than dump more money in an (at the time) eight or 9 year old truck he'd have them bypass the relay. but maybe at the time relays cost more than they do now.
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Senior User
Joined: May 2008
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From: Bentonville, AR
I sat in the truck for about 10 minutes...it did this the entire time. Maybe if I let it run longer it would stop.
Once the engine is warmed up I do not see the need for the glow plugs to come one. I could be wrong but I wanted to throw it out there for anyone to comment.
I certainly understand the need for glow plugs in the winter (or cold summer mornings).
Tim
Once the engine is warmed up I do not see the need for the glow plugs to come one. I could be wrong but I wanted to throw it out there for anyone to comment.
I certainly understand the need for glow plugs in the winter (or cold summer mornings).
Tim
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Post Fiend
Joined: Nov 2003
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From: Nutter Fort, WV
It was common for the 86 and older control module to fail and turn the glow plugs on when not needed.
The system is rather complex, and trouble shooting is a nightmare.
Glow, after glow timer, latching relay, coolant temp sensor, relay to name a few components all in different locations with different inputs.
87 and newer systems, about all that could turn the glow plugs on when not needed would be a controller failure, much simpler to diagnose.
The system is rather complex, and trouble shooting is a nightmare.
Glow, after glow timer, latching relay, coolant temp sensor, relay to name a few components all in different locations with different inputs.
87 and newer systems, about all that could turn the glow plugs on when not needed would be a controller failure, much simpler to diagnose.
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just so i'm straight on this, the glow plug controller is infact that "starter solenoid" looking thing just between the engine and the firewall, under the air filer? that's all that controlls the glow plugs? it measures g/p temperature and whatever else? i just want to make sure because it seems so simple of a device to perform all those funtions. is there a thermocouple or something inside each glow plug that sends the temperatur to the controller? sorry to ask so many questions. just wanna make sure i have all the facts before i tear into somthing
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
timcos,
On the older systems, you should see after glow when the temps are around 30 degrees or lower.
At temps in the 80's, something is wrong.
Something tells me that when temps do drop, the glow plugs will be on almost constantly, which will result in very short glow plug life.
tpolley, the glow plug relay and controller is located at the rear of the intake manifold on 87 and newer engines.
The controller is solid state, and it measures the resistance change in the glow plug circuit as the glow plugs heat.
The way it measures the resistance change is what makes the newer systems so sensetive to burnt out glow plugs.
One burnt plug changes the resistance of the circuit and makes it short cycle.
On the older systems, you should see after glow when the temps are around 30 degrees or lower.
At temps in the 80's, something is wrong.
Something tells me that when temps do drop, the glow plugs will be on almost constantly, which will result in very short glow plug life.
tpolley, the glow plug relay and controller is located at the rear of the intake manifold on 87 and newer engines.
The controller is solid state, and it measures the resistance change in the glow plug circuit as the glow plugs heat.
The way it measures the resistance change is what makes the newer systems so sensetive to burnt out glow plugs.
One burnt plug changes the resistance of the circuit and makes it short cycle.
Senior User
Joined: Dec 2007
Posts: 108
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From: Colorado Springs, CO
I had the opposite happen tonight, my after-glow didn't after-glow, though I'm used to it happening. I am having hard starting trouble, and am wondering about an ohm test on the glow plugs. When I tested them the ohm meter would zero out about 1/4" from the body, but would not zero out on the tip. I remember before putting them in I ohm tested them and they zero'd out all the way to the tip. Will a glow plug that is still good not zero out at the tip once used, or are all the glow plugs bad and need replaced? Thanx
Tuned
Joined: Jun 2008
Posts: 293
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From: Huntsville,Ont.
Get a circuit tester the kind that hooks to your battery, clip the end of the lead to pos on the battery and take the lead off the glow plug, touch the probe to the terminal and if it lights, the plug is likely good.
A continuity tester is a better way to do it.
But a bad plug is a bad plug, no in between.
A continuity tester is a better way to do it.
But a bad plug is a bad plug, no in between.
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
When you use an ohm meter, it has to be a decen meter to get a good reading.
.5 to 1 ohm is very close to a dead short.
A cheap meter will probably just show a dead short or 0 ohms.
When you test a plug, one lead on the connector and the other on the threads where it screws into the head.
.5 to 1 ohm is very close to a dead short.
A cheap meter will probably just show a dead short or 0 ohms.
When you test a plug, one lead on the connector and the other on the threads where it screws into the head.
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