Vacuum gauge
Typical vacuum gauge readings
1. Low constant pressure
2. Low fluctuating pressure
3. Regular pressure surges
4. Random pressure surges
5. Rapid vibration of the arrow
6. Strong pressure fluctuations
7. Constant decrease in pressure
Connect the meter to the intake manifold. Warm up the engine and let it idle.
If the engine is in good condition, the gauge should read 17-22 inches and the needle should twitch evenly.
If the meter readings are lower than required, the following are likely causes: a leaking gasket between the intake manifold and the carburetor or throttle body, a leaking vacuum hose, or an out-of-adjustment of the ignition timing or camshaft rotation angle.
If the meter readings are 8 inches below normal, the intake manifold gasket is leaking or the injector is faulty.
If the needle drops 2 inches below the normal mark at regular intervals, the valves are leaking.
If the arrow jerks downwards very unevenly, the valve is stuck or the spark plugs are faulty.
Four inch needle vibration and exhaust fumes - valve guides are worn.
Rapid vibration when increasing engine speed - a leaking intake manifold or head gasket, worn valve springs, burnt valves, or faulty spark plugs.
A slight twitching of the arrow near the normal 1 inch mark indicates problems with the ignition.
Strong twitching of the needle - the cylinder head gasket is damaged.
If the needle slowly moves over large distances, the fuel is not mixed correctly, or the intake manifold or throttle body gasket is leaking.
Increase the RPM to 2500 and turn off the engine, the needle should drop to almost zero, then rise 5 inches above the normal mark and return to the normal mark.
If this does not happen, then the piston rings are worn out.
If there is a long delay, the exhaust system is clogged.
[The article is copied from the resource: www.MazBook.ru]