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Vacuum Gauge - What is it telling me? 200

posted by  someone claiming to be jorn on  Sun Jan 25 19:52 CST 2004 [RELATED]

Well you measure the air pressure between the throttle valve and inlet valves (the inlet manifold pressure).

At idle or under low load the engine is sucking for air, while the throttle is near closed, a low pressure (vacuum) is the result. When the engine is under load it gets plenty of air as the throttle is wide open, the pressure is high or near outside air pressure. Install a turbo and the pressure is higher than outside air pressure.

There is some pulsation as the pistons move up and down and the inlet valves open etc, but it should not be that much. My guess is that you see some air resonance due the other items hooked up to the vac hose you chose.

You could have some serious leakage past the inletvalve, blowing exhaust back into the inlet manifold, but your engine should run really unstable...

There are spare threaded holes in the manifold, go the junkyard and unscrew a fitting from a B2XX engine, fit it on your car and connect up. Should be steady.

Reg,

Jorn






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