How to test glow plugs?

[jim x 3]

Tim, where did you get the test you recommend? I have never heard of that (I do find it interesting though). I know the gps resistance changes under load and have always kinda wondered how to check it. I do wonder about the setup though. 12v / .3 ohms = 40 amps, which is above the limit of my dvom (internal fuse is 10 amp).

punk

Punk,

Just like an incandescent light bulb, our GPs have a positive temperature coefficient, meaning the resistance thru the GP rises with temperature. So as the GP heats up, the resistance rapidly rises. Your equation above won't hold (for very long). But Tim's method is goofy nonetheless (and he has his meter hooked up backwards).

Regards,

 

[punkmechanic]

I think his methodology (i.e. theory) is sound. I was just wondering where he learned it. I was new to diesels 3 years ago, but between vw, the ford dealer Im at now, school (uti for anyone that is interested) and all the sidework and research I cant really call myself a nooby anymore. That said I learn something new everyday (hence the reason I love being a tech, never gets old).

I was rolling his method over in my head and I think an amp clamp type device (magnetic inductance reading) would work and could actually test the varing resistance as the gp heated.

on a similaiar note I have always wondered if a programer could be set up to read real time ohm load on a gp, during engine operation. Sounds crazy but, by doing this you could use the gp as a thermocouple in each cylinder. I doubt it would be real precise but a half second on time every "x" amount of time could give you a digital readout (via the programmer) of each cylinder's (aproximate) egt. Seems like a good way to monitor which injector is going down when you notice a miss and smoke.

Not sure if it would work or not. Gonna have my buddy that deals with computers look into what kind of programmer would be capable of it, and see what happens to gp resistance at various temps (blow torch + old yet decent gp = "testing 1 2 3)

punk

 

[Agnem]

For me, I've never had the test light method let me down. I just replaced these 5 the other night. I only had 3 glow plugs that would light the test light brightly. These 5 were completely dark.

One of them is a little scary looking. Thanks to WMO, these boys died young.

You must be registered for see images

 

[jim x 3]

I think his methodology (i.e. theory) is sound. I was just wondering where he learned it. I was new to diesels 3 years ago, but between vw, the ford dealer Im at now, school (uti for anyone that is interested) and all the sidework and research I cant really call myself a nooby anymore. That said I learn something new everyday (hence the reason I love being a tech, never gets old).

I was rolling his method over in my head and I think an amp clamp type device (magnetic inductance reading) would work and could actually test the varing resistance as the gp heated.

on a similaiar note I have always wondered if a programer could be set up to read real time ohm load on a gp, during engine operation. Sounds crazy but, by doing this you could use the gp as a thermocouple in each cylinder. I doubt it would be real precise but a half second on time every "x" amount of time could give you a digital readout (via the programmer) of each cylinder's (aproximate) egt. Seems like a good way to monitor which injector is going down when you notice a miss and smoke.

Not sure if it would work or not. Gonna have my buddy that deals with computers look into what kind of programmer would be capable of it, and see what happens to gp resistance at various temps (blow torch + old yet decent gp = "testing 1 2 3)

punk

Punk,

Yes Tim's theory was correct.

An amp clamp would work - but you would need to be quick to measure - analog meter would be better than digital.

And yes, the (unpowered) GPs would vary grossly in resistance according to their ambient temperature. But to use them to monitor cylinder temp, you would need to calibrate to a specific GP brand and part (and there may still be considerable variation) and the GP wiring would need to change so that you can measure individual GP resistance (for per cylinder temps) instead of an average for the entire bank or engine. And this is what the GP controller does (it actually measures voltage drop thru the shunt, which is a measure of amps thru the GPs, which is related to average GP resistance and temp) to determine how to power the GPs. And this is why it gets confused when some GPs are bad - system resistance is higher than normal for a given temp.

Regards,

 

[jonathan]

hook them up to a battery charger the neg to the part were a socket goes the hot on top if they light up they work thats what i did and found out 4 of mine were bad