[Vwdiesel] glow plug test -GP's as thermocouple sensors

[Sandy Cameron]

At 10:54 PM 5/3/05 -0400, you wrote:
  DID YOU KNOW that the glow plugs also act as a
>thermocouple?  You can put a DMM in low DC millivolts range DC between a
>glow plug and engine earth connection and actually measure a low voltage
>(~10-25 mV) which is indicative of cylinder compression (senses compression
>heat) during cranking, and also how well each cylinder is firing in relation
>to its neighbors!?  You can set up four inexpensive DMM displays and monitor
>a running engine in real time.  If a piece of crap goes through an injector
>and the cylinder stumbles you really see it instantly on the GP voltage
>output.  It would be interesting to put a 4 channel A/D converter on these
>'sensors' and gather data during a run.

THIS IS VERY INTERESTING!  I see cTc has/had dmms on sale for $10 this week
or last. 4 of them racked up would provide a very interesting performance
analyzer. I will try it.

I had a strange problem recently on goldie, simply solved once understood.
The glow plug "sensors" would have aced it instantly.

Missing on one cyl at idle
Head gasket replaced 2 months ago
problem got worse with time
I went with wrench in hand to slack off the injector unions one at a time to
identify the bad cyl. (the glow plug "sensor" would have done that for me)
There were no obvious leaks anywhere, but I noticed the back end of the pump
was a little "damp" with fuel. Checked the pump end unions and was able to
draw all of them up at least a quarter turn. Engine then idled perfectly.
There had been no drip. the amount of lost fuel that prevented firing on the
one cyl would evaporate before it could form a drip.

It sure doesn't take much to keep these things turning over at idle.

I am reasonably sure I tightened them properly after the head gasket job.
Cold flow of the unions, perhaps?

Sandy