Another use for Glow Plugs? Combustion Temp Sensors

[JOAT]

Ran across this thread on the bio-infopop. Something I had heard about years ago but forgot. That thread goes into many uses for the test, but I'll present it more from a simple diagnostic perspective.

Because of the different materials in glow plugs, they will produce a tiny voltage, varying at different temps. They also will have a change in resistance. By disconnecting the glow plugs from the main wiring while not being used, you can measure the millivolts or resistance change from terminal to ground. While it would be a wiring pain, once you had a base for each cylinder when the engine was running properly, you could compare those results when the engine started behaving odd.

Say at highway speeds you have a fictional resistance of say 2 ohms on each cylinders GP. You start noticing excessive white start up smoke and rough idle. If it were due to a broken nozzle spring, that cylinder would likely operate at a different temp, so the reading on that GP would change.

Just thought I'd throw that out there. I may at some point build a modified GP wiring harness so I can try it myself.

 

[Dieselpwrdredneck]

That is awsome, definatly something to ponder over
Good job on finding this

keep us updated

Neal

 

[dpantazis]

thermocouple

joat-
what you are describing is the gp behaving like a thermocouple.
might be worth 'sprementing with a DMM that has theromocouple capability to see what it actually does.

that asdide, how would we wire this up? a second wiring harness from the under the VC's?

dp

 

[lukecline]

im pretty sure jody tipton uses the gp holes for pressure reading equipment when he does cylinder pressure tuning. Im not sure if those also read temps, but i wouldnt be suprised if they do.

 

[JOAT]

joat-
what you are describing is the gp behaving like a thermocouple.
might be worth 'sprementing with a DMM that has theromocouple capability to see what it actually does.

that asdide, how would we wire this up? a second wiring harness from the under the VC's?

dp

Yeah, thermocouple for the milliamp reading, or a thermister for the resistance change.

I was thinking of re-routing each GP wire (external wiring) to a PCB with 8 mini relays. That way when the GP's are on, the relays allow full voltage to them, and when they are off, they would be disconnected from each other and could be read individually.

 

[Dieselpwrdredneck]

what would you use to read each individual GP at the same time, a data logger or data aquisition system?

 

[JOAT]

Depends how much $$$ you want to spend. Cheapest would be to just read one at a time.

I see you have a homemade breakout box in your sig. Does it break out the individual GP's too?
If so you could be ready to try it out

 

[Dieselpwrdredneck]

Unfortunatly it does not break out the GP's individually..... well not yet anyway , might be somethin to try in the future

Would this theory be true with any GP or just PSD GP's? I woud think any.

i would love to get a logger, someday

 

[JOAT]

Should be any Glow Plug.

 

[MADVAN]

Joat
Do you know max load of one GP?
8 mini relays might reak havoc on an allready crappy GP system.

Maybe an AIH for startup and gp's for temp testing.

Bill