Posted by gary on May 01, 2000 at 16:58:16:
In Reply to: manifold vacuum problems posted by m clark on April 29, 2000 at 00:09:42:
I agree with Steve. Ignition timing (especially retarded) will definitely
drop the numbers. The idle reading
should be around 18-20. On hard deceleration (coasting downhill) it will
go up and on full-throttle uphills it will go down.
Grinding up a hill in a high gear is bad for main bearings and things and will drop that gauge
to almost zero. That's why they put the gauge there. It is supposed to be an
indicator of abuse. Low readings are considered "bad". They also indicate heavy fuel consumption.
I would worry about two things;the idle reading and driver habits.
A tired engine will also read low at idle. If a general tuneup will not bring the
gauge past 15 and the gauge is accurate and there aren't any leaks then it's time
to check compression. Very low readings up hills indicate a heavy foot in too high a
gear.