chrisgrant91
Full Access Member
what are the signs its going out.... it doesnt seem to being on as long as it should
glow plug controller
- Thread starter chrisgrant91
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chrisgrant91
Full Access Member
i couldnt tell ya...i havent had the truck too terribly long.. but from what ive glanced at they look newer. how do you tell?
argve
Resident Fruitcake
How the glow plug controller works is like this.
When power is applied to the circuit the controller is looking at the ratio of voltage dropped across the big zig zag piece of metal on the controller vs the voltage dropped across the glow plugs. Now you need to understand the glow plugs are all in parallel so they will have an extremely low resistance so their voltage drop will be very very low so the voltage drop across the zig zag is high then as the glow plugs heat up their resistance increases so they start to drop more voltage. The controller will shut off the power to the circuit when the voltage across the zig zag resistor get low enough.
Now if you have even just one bad glow plug the circuit will change in it's resistance value causing the resistance across the glow plug portion of the circuit to increase. Now remember that as they heat up their resistance increases so the controller assumes they are hot so it starts cycling them to keep them from burning up. So even just one bad glow plug will fool the controller into thinking that they have already heated up, causing a hard or no start condition.
How to check a glow plug...
Take a cold engine and your ohm meter and test the resistance of each glow plug - a cold glow plug will come in at around 1~2 ohms (almost a dead short). If it's shows a high resistance then that plug is bad.
Most here will tell you only to run Motorcraft Branded plugs or part number zd-9 from Autozone because both of these plugs are the same and they have the best track record of not swelling the tips when they go bad. If the tip swells then you have a problem on your hands of getting the plug out without breaking the tip off and parts of the glow plug being left in your combustion chamber. If the tip gets broken you need to the parts out of the cylinder BEFORE you start it because there isn't enough room in the chamber when the piston is at TDC for anything of that size to be in there so they will get pounded into the top of piston and could cause more damage than you want.
When power is applied to the circuit the controller is looking at the ratio of voltage dropped across the big zig zag piece of metal on the controller vs the voltage dropped across the glow plugs. Now you need to understand the glow plugs are all in parallel so they will have an extremely low resistance so their voltage drop will be very very low so the voltage drop across the zig zag is high then as the glow plugs heat up their resistance increases so they start to drop more voltage. The controller will shut off the power to the circuit when the voltage across the zig zag resistor get low enough.
Now if you have even just one bad glow plug the circuit will change in it's resistance value causing the resistance across the glow plug portion of the circuit to increase. Now remember that as they heat up their resistance increases so the controller assumes they are hot so it starts cycling them to keep them from burning up. So even just one bad glow plug will fool the controller into thinking that they have already heated up, causing a hard or no start condition.
How to check a glow plug...
Take a cold engine and your ohm meter and test the resistance of each glow plug - a cold glow plug will come in at around 1~2 ohms (almost a dead short). If it's shows a high resistance then that plug is bad.
Most here will tell you only to run Motorcraft Branded plugs or part number zd-9 from Autozone because both of these plugs are the same and they have the best track record of not swelling the tips when they go bad. If the tip swells then you have a problem on your hands of getting the plug out without breaking the tip off and parts of the glow plug being left in your combustion chamber. If the tip gets broken you need to the parts out of the cylinder BEFORE you start it because there isn't enough room in the chamber when the piston is at TDC for anything of that size to be in there so they will get pounded into the top of piston and could cause more damage than you want.
chrisgrant91
Full Access Member
is there a way you can tell if its swelled? like stop before you break it?... or are they super fragile? and when it comes down to it would you have to pull the head off?
sle2115
NRA LIFE MEMBER
Here is a good read for you - Zigg's Glow Plug Article
Great write up by Travis (argve) as well, a good explanation of how it all works. Zigg figured a way to possibly save head removal in his article above.
Great write up by Travis (argve) as well, a good explanation of how it all works. Zigg figured a way to possibly save head removal in his article above.
chrisgrant91
Full Access Member
that made alot of sense... but what im saying is... can you tell if they are gunna break? or is it just somtimes they do and somtimes they dont... or do you really have to wrench on them to break
jimraelee
Full Access Member
I recnently had a similar issue... short GP time. I found that small corosion around the terminals of the GP controller to be the fault... pulled the controller and wire brushed the connections, all was good after that. typical 7-10sec GP heat time.
chrisgrant91
Full Access Member
what do you probe to check ohms?
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