3.1. Vacuum gauge readings options for engine fault diagnostics
2. Connect a vacuum gauge to the intake manifold. Start and warm up the engine to normal operating temperature.
3. Read the vacuum gauge readings.
If the engine is in normal condition, the vacuum gauge readings should be constant and be 430÷560 mm Hg.
Low constant vacuum readings indicate a damaged gasket between the intake manifold and the throttle body, a damaged vacuum hose, incorrectly set ignition timing, or incorrectly set valve timing.
If the vacuum gauge readings are 80÷200 mm Hg below the norm and fluctuate, then the intake manifold gasket near the inlet may be damaged or the injector may be faulty.
If the readings constantly drop by 50÷100 mmHg relative to the stable value, then the valves may be damaged. In this case, you should measure the compression in the engine cylinders (see Section 2).
(Information published on the website: Skodabook.ru)
If the readings drop, but not regularly, then the valve may be stuck or there is an ignition failure.
If the readings fluctuate rapidly with an amplitude of about 100 mmHg at constant idle speed and smoke comes out of the exhaust pipe, the valve guides may be damaged.
If the reading fluctuates rapidly as the idle speed increases, the intake manifold gasket or cylinder head gasket may be damaged, the valve springs may be weak, the valves may be burnt, or the ignition may be malfunctioning.
Small fluctuations of about 25 mm Hg are usually associated with problems in the ignition system.
If the readings fluctuate greatly, the cylinder head gasket or cylinder may be damaged.
If the needle moves slowly over a wide range of values, the crankcase ventilation system may be clogged, the intake manifold gasket or the gasket between the throttle body and the manifold may be damaged.
4. Check how quickly the vacuum gauge readings are restored after a sharp and full opening of the throttle valve and its return to its original position. If the engine is in normal condition, the readings drop to almost zero, then rise to about 130 mmHg above normal and drop again to the previous values at constant idle speed. If the readings recover slowly and go through the maximum after the throttle valve is closed, then the piston rings may be damaged. If there is a long delay, the exhaust system may be clogged.