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Checking the engine by means of the vacuum gauge

Using the gauge, you can get information about the state of the engine and determine that the broken cylinder head gasket, damaged power supply system, piston rings or valves, improperly adjusted fuel injection system, etc. Unfortunately, the gauge readings can be misinterpreted, so these measurements should be used in conjunction with other methods of checking the engine. For the correct definition is important as the absolute value of the vacuum reading, and their rate of change.

Options for reading the gauge in the diagnosis of malfunctions of the engine

Connect the vacuum gauge to the intake manifold. Start and warm up the engine to normal operating temperature.

Consider the testimony of the gauge.

• If the engine is in normal condition, the gauge readings should be constant at 430 ÷ 560 mm Hg. Art.
• Low constant gauge readings indicate damage to the gasket between the intake manifold and the throttle body, vacuum hose is damaged, improperly installed ignition point or improperly installed timing phases.
• If the gauge readings below normal at 80 ÷ 200 mm Hg. Art. and fluctuate, it may be damaged gasket intake pipe near the inlet or faulty injector.
• If the readings are constantly falling on the 50 ÷ 100 mm Hg. Art. relatively stable values, it may be damaged valves. In this case, measure the cylinder compressions (see. Section Checking compression pressure).
• If the readings are falling, but not regularly, then maybe it jammed valve or a malfunction occurs in the ignition.
• If the permanent idle readings rapidly oscillate with an amplitude of about 100 mm Hg. Art., and from the exhaust smoke, possibly damaged valve guides.
• If the readings fluctuate rapidly with increasing idle speed, it may be damaged intake manifold gasket or cylinder head gasket, weakened valve springs, valves or burned there is a failure in the ignition.
• Small fluctuations around 25 mm Hg. Art. normally associated with failures in the ignition system.
• If the readings vary greatly, it may be damaged cylinder head gasket or cylinder.
• If the needle is slowly moving in a wide range of values, it is possible that the controlled system is clogged crankcase ventilation, intake manifold gasket is damaged or the seal between the throttle body and the pipe.

Check how fast the gauge readings are restored after a sharp and wide open throttle position and its return to its original position. If the engine is in a normal state, indications fall almost to zero, and then increases by about 130 mm Hg. Art. above the norm and again decrease to former values at constant idle. If the readings are restored slowly and pass through a maximum after closing the throttle, then maybe damaged piston rings. If there is a long delay, it may be clogged exhaust system.