[Vwdiesel] Monitoring GPs how it operates...with just 4 LEDs

[Mark Shepherd]

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 d Iode'
> 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...

Mark,

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

Shawn everyone of my 12 glowplugs that have failed have
failed open circuit. Whilst this is not many in the scheme
of things; from my point of view its all of them... I am
relying on the indication of a failed GP to be opencircuit/
high resistance which would cause the LED to extinguish as
its relying on the 1 ohm GP to make the circuit. Whilst
power is glowing GP the LED terminals would both be at
12volts ish and so unlit. this would also show cycling  of
GPs by long interval 'flashing' .

Miser