In case of decrease in engine capacity (at serviceable power supply systems and ignitions) inspect a compression in cylinders (see подразд. 3.1.3).

To define a condition of the engine it is possible also by means of the vacuum gage. For receiving the correct results this way of check is recommended to be combined with other ways. Before check it is necessary to connect a vacuum gage hose to an inlet collector, to start up the engine and to warm up it to normal working temperature.

If pressure in an inlet collector makes 430–560 mm of mercury., and the arrow of the vacuum gage is in rest, an engine condition the normal.

If pressure in an inlet collector is much lower than 430 mm of mercury., and the arrow of the vacuum gage is motionless, the following malfunctions of the engine are possible: laying between an inlet collector and the butterfly valve case is damaged, the vacuum hose is damaged, the moment of ignition or a gazoraspredeleniye phase are incorrectly established.

If indications of the vacuum gage are lower than norm on 80–200 mm of mercury. and his shooter hesitates, that, possibly, laying of an inlet collector is damaged or the injection system is faulty.

If pressure falls on 50–100 mm of mercury., and then comes back to a reference value with some periodicity, it can testify to valve damage. In this case it is necessary to measure a compression in cylinders.

If pressure falls, but is irregular, jamming of the valve or admissions in ignition can be the possible reason for that.

If at constant frequency of rotation of a cranked shaft idling the arrow of the vacuum gage quickly fluctuates with amplitude of change of indications about 100 mm of mercury., and from an exhaust pipe there is a black smoke — directing plugs of valves are damaged. If the arrow quickly fluctuates at increase in frequency of rotation — laying of an inlet collector or laying of a head of the block of cylinders is damaged, springs of valves are weakened, valves scorched or there are admissions in ignition.

Small fluctuations of pressure about 25 mm of mercury. are usually connected with failures in ignition system.

At arrow fluctuation with big amplitude — laying of a head of the block of cylinders or the cylinder are damaged.

If the arrow slowly moves in a wide range — the system of ventilation of a case is littered, laying of an inlet collector or laying between the case of a butterfly valve and an inlet collector is damaged.

Check, pressure in an inlet collector after complete opening of a butterfly valve is how fast restored. For performance of this operation it is necessary to address to the assistant, which should press against the stop an accelerator pedal, and then release it. By pedal pressing pressure should fall almost to zero, and then increase approximately by 130 mm of mercury. higher than norm and quickly to return to normal value at the established frequency of rotation of a cranked shaft idling. If pressure is restored slowly and its value passes through a maximum after butterfly valve closing, it can testify to damage of piston rings. If the delay is longer, the system of production of the fulfilled gases is littered.