Automotive Technology/Engine Vacuum Test

The vacuum gauge should be directly connected to the intake manifold. Desirable vacuum is 17 to 22 inches of vacuum.

Readings
 * Slightly low reading shows late ignition timing


 * Very low but stay shows intake manifold has a significant leak


 * if on idle, you slowly go back and forth 11 and 16, you have a fuel problem


 * burned and leaky valve fluctuate between 12 and 18


 * Weak valve springs fluctuate between 10 and 25


 * leaky Head Gasket between 7 and 20


 * sticking valve between 14 and 18


 * on acceleration and high rpm, if vacuum slowly rises, exhaust restriction