[Vwdiesel] Monitoring GPs how it operates...

Shawn Wright swright at zuiko.sls.bc.ca
Thu Dec 23 10:52:59 EST 2004

On 23 Dec 2004 at 10:23, Mark Shepherd <mark at shepher.fsnet.co.uk> wrote:

>  As my descriptions are fairly 'piss poor' to say the least
> confusion is likely to reign which is why I'm going to
> explain operation (as I see it)...
> After car has started (or not) power to the glowplugs
> naturally turns off. These 4 circuits I'm introducing  now
> use the glowplugs as a route to earth and the 4 LEDs will
> glow if their +ves are powered up.
> Once the plug dies and its driving supply switches off there
> is now no earth and the LED goes out as the 'power dode'
> stops the LED doing a 'terminator' and re-routing through
> the other good GPs }8OD)
> Your  (my Patent) pretty display now shows only 3 out of 4
> LEDs glowing...Bingo :o) You can now say to your passenger
> service on no.2 cylinder required...


This sounds interesting, but I wonder how it will work if the GP does not fail "closed". 
I have at least 6 dead GPs in the garage now, and I'm pretty sure some of them 
failed with a high resistance in the 10k ohm range. This would equate to one mA of 
current - is this enough to light an LED? I don't know...I suppose if it did, it would be 
very dim.
It might be helpful to have stats on the failure modes of GPs, percentages of failed 
open vs failed high resistance.--
Shawn Wright
I.T. Manager
Shawnigan Lake School

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