In case of deceleration of power of the engine (at serviceable power supply systems and ignitions) carry out an inspection of a compression in cylinders (see subsection 3.1.3).

It is possible to determine a condition of the engine also by the vacuum gage. For obtaining 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 launch the engine and to warm up it up to the 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, that condition of the engine normal.

If pressure in an inlet collector is much lower than 430 mm of mercury., and the arrow of the vacuum gage is not mobile, the following malfunctions of the engine are possible: laying between an inlet collector and the case of a butterfly valve is damaged, the vacuum hose is damaged, are incorrectly determined the moment of ignition or phase of gas distribution.

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

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

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

If with a constant frequency of rotation of a bent shaft idling the arrow of the vacuum gage quickly fluctuates with an amplitude of change of indications about 100 mm of mercury., and from an exhaust pipe there is a black smoke — the 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, burned valves or there are admissions in ignition.

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

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

If the arrow slowly moves in the 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 full opening of a butterfly valve is how fast restored. For performance of this operation it is necessary to address the assistant who has to press against the stop an accelerator pedal, and then release it. When pressing a pedal pressure has to reduce almost to zero, and then increase approximately by 130 mm of mercury. higher than norm and quickly to return to normal value with the established frequency of rotation of a bent shaft idling. If pressure is restored slowly and its value passes through a maximum after closing of a butterfly valve, then it can demonstrate damage of piston rings. If the delay is longer, then the system of production of the fulfilled gases is littered.