SJ Audi 100 Won't Start (Vacuum Leak?)

[Huw Powell]

> TESTING OF POTENTIOMETER DURING STARTUP:
> Previously I'd tested the potentiometer resistance with the bonnet open.
> I'd found that The resistance between the bottom and the middle contact is
> about 2 kOhms at rest and rises to a max of about 13kOhms near full open
> falling slightly to 11kOhms at full open.  Today I decided to measure this
> resistance during an attempted start just to ensure that the plunger is
> actually moving.  The resistance moved from about 2 kOhms up to about 4 or 5
> kOhms. when it appeared that the engine was about to start and then as it
> sputtered the resistance fell back to 2kOhms.

Something about this has been bothering me since I read it... mostly 
because the pot. acts as a voltage divider on a 5v/G feed from the ECU.

Of course, measuring the varying resistance should be a fine way to see 
if it is clean and tracking properly, with the power off.

But while cranking/running etc., how can you measure a resistance that 
has voltage across it?

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/