Basic positions and fluctuations of the gauge needle when diagnosing engine malfunctions
1. Connect the vacuum gauge to the inlet pipeline. Start and warm up the engine to normal operating temperature.
2. Read the vacuum gauge readings:
- If the engine is in normal condition, the gauge reading should be 430-560 mm. rt. Art., and the needle of the vacuum gauge should be in place.
- Low continuous readings vacuum gauge indicate that the gasket between the intake manifold and the throttle body is damaged, the vacuum hose is damaged, the ignition timing is incorrectly set, or the valve timing is incorrectly set.
- If the vacuum gauge reading below the norm by 80 - 200 mm. rt. Art. and hesitate then the inlet pipe gasket near the inlet may be damaged or the injector may be defective.
- If the testimony constantly fall by 50 - 100 mm Hg. Art. relatively stable value, the valves may be damaged. In this case, it is necessary to measure the compression in the engine cylinders.
- If the testimony fall, but not regularly, then the valve may be stuck or there is a malfunction in the ignition.
- If the testimony oscillate rapidly with an amplitude of about 100 mm. rt. Art., at constant idle speed, and smoke comes out of the exhaust pipe, the valve guides may be damaged.
- If the testimony fluctuate rapidly with increasing idle speed, then 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 misfiring.
- Small fluctuations of about 25 mm Hg. Art. usually associated with failures in the ignition system.
- If the testimony fluctuate a lot then the cylinder head gasket or cylinder may be damaged.
- If the arrow moves slowly over a wide range of values, then the crankcase ventilation system may be clogged, the intake manifold gasket or the gasket between the throttle body and the pipeline is damaged.
3. Check how quickly the readings of the vacuum gauge are restored after a sharp and full opening of the throttle valve and returning it to its original position. If the engine is in normal condition, the reading drops to almost zero, then rises by about 130 mm. rt. Art. above normal and again decrease to the previous values at constant idle speed. If the reading recovers slowly and goes through a maximum after closing the throttle, then the piston rings may be damaged. If there is a long delay, then the exhaust system may be clogged.