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Needle position Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 22 Oct 2002 12:44:22
In Reply to: If yellow/white when engine is off ->Atmp Pressure (+), roman, Tue, 22 Oct 2002 09:05:41 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With the car off, the needle should point to the gap between the white and yellow bands. That's atmospheric pressure. Depending on the barometric pressure that day, it might shade a hair towards the upper or lower part of that gap. But unless you're on top of a mountain or the eye of a hurricane, it'll be right at that gap.
If it isn't pointing to that gap with the engine off, there is a mechanical problem with the gauge. No vaccum leak will affect it, because with the engine off, all parts of the system are at atmospheric.
With the engine idling, the needle should be in the white. Actually, quite far into the white. With the engine idling, you have very high manifold vacuum. The other time the needle will be in the white is if you're driving along and you take your foot off the gas pedal. With the throttle plate closed, the engine acts as a pump, pulling vacuum in the manifold. The max vacuum would be going down hill at speed, in gear, with your foot off the throttle.
Driving along, the needle will fluctuate between the top of the white and somewhere into the yellow.
If the gauge isn't moving and points to the white/yellow gap all the time, then the hose has fallen off the gauge. If the gauge always points to 12O'clock, it's a mechanical problem. If it moves, but just not to where you expect it, it could be hoses or a mechanical gauge problem.
Good luck!
posted by 192.249....
, Mon, 21 Oct 2002 20:02:19, Tue, 22 Oct 2002 12:44:22 <-- Viewing This Message
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