mankypro
Learning Slowly...
Other than hard starts or not starts at all is there a whay to determine the status of a glow plug without removing it?
Determing the status of a glow plug while it's still in the vehicle
- Thread starter mankypro
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LUCKY_LARUE60
Full Access Member
Test light, one end to neg side of battery the other to glow plug with wire off. If light lights up it's good, if no light then it's bad, works every time.
Jim
Jim
KR69IDI
Full Access Member
Are you sure about this? Shouldn't one side of the test light be on the pos batt post. and the other to the glow plug terminal with the wire unplugged.
LUCKY_LARUE60
Full Access Member
mankypro
Learning Slowly...
May I ask about the electrical theory behind this?
Think of it as a light bulb with a very heavy duty filament. If the filament is in good condition the resistance is minimal (the <2 ohms deal). If the filament is broken the resistance will be infinity. If the filament is 'starting to wear out' the resistance will go up and therefore you'll have a higher reading but not infinity. The test light method will work but you have to make sure you watch how 'bright' the test light is on each glow plug (the intensity needs to be the same) since a weak plug will not be as bright as a good one.
reklund
Full Access Member
A glow plug is simply a conductor. If it is working properly, it will provide a path to ground through the glow plug. As electricity flows through the glow plug, the resistance of the heating element creates heat, warming the pre-chamber. Applying voltage with a test light is simply observing if the ground is good. Good ground means the glow plug is either shorted or heating up normally. Typically, these glow plugs go "open" when the fail, meaning there is NO path to ground, and the plug needs to be replaced.
Think of the glow plug just like a light bulb. All a light bulb does is "glow" due to the resistance in the element. The electricity flowing through the resistor creates heat, which you see as light being emitted from the bulb. If the element is broken, the light bulb doesn't work, since there is no way for the electricity to flow back to ground. Same thing goes on with the glow plugs in our trucks.
Did I word that correctly?
Ryan
Think of the glow plug just like a light bulb. All a light bulb does is "glow" due to the resistance in the element. The electricity flowing through the resistor creates heat, which you see as light being emitted from the bulb. If the element is broken, the light bulb doesn't work, since there is no way for the electricity to flow back to ground. Same thing goes on with the glow plugs in our trucks.
Did I word that correctly?
Ryan
Last edited:
IMHO you did
mankypro
Learning Slowly...
Thank you for the awesome 'splanations!
JwS
Full Access Member
My experience was that this is not always reliable, I checked my glowplugs more than once and carefully, and all tested good, but my controller still didn't cycle right (too short). I cleaned and checked all other connections, and was thinking I needed a new controller, but I figured I'd change the GP's first just to be sure, I did that and it then worked like it should, and still does!
JwS
JwS
mankypro
Learning Slowly...
The reason I'm asking is because I just switched out all the gp's on my truck with the heavy duty ac delcos. The truck being new to me has never sounded or fired up as smartly (and it fired up easily before this) or had the acceleration I now have. It's like having a new vehicle. I had 7 dead plugs - didn't even know it.
jimraelee
Full Access Member
WOW 7 bad, I'm suprised you even started that thing without a bbq burning under that engine...
Diesel JD
Full Access Member
They'll start like that if they have good compression. One or two is sometimes enough with the 6.9 system. You have the heavy duty AC delcos, did you get the 12V ones? How much did they cost and how long are you leaving them on.
mankypro
Learning Slowly...
I'm still using the controller as I haven't gotten around to hot wiring the momentary switch as I don't have a good idea of how to do it yet. The stealer ship replaced the controller. The plugs were $22.00 ea
I really want to get that switch wired in tomorrow - I'm online right now trying to find someone who has documented the process so I can follow it.
I really want to get that switch wired in tomorrow - I'm online right now trying to find someone who has documented the process so I can follow it.
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