Depression measurement is reliable and rather inexpensive way of diagnostics of the engine. Under vacuum gauge indications it is possible to receive representation about a condition of piston group, about tightness of a lining of a head of the block of cylinders, inlet and final collectors, correctness of adjustments of power supply systems and release of the fulfilled gases, throughput of the fulfilled gases, a condition of valves (them залипания or burn-outs) and springs of valves and also to check up correctness of adjustment of the moment of ignition and phases timing at engine work.
Unfortunately, vacuum gauge indications are difficult for interpreting, and results of the analysis of indications can be erroneous, therefore vacuum diagnostics expediently unite with other methods.
Initial factors on which indications of the vacuum gauge are analyzed and the most exact conclusions about an engine condition become, the absolute instrument reading and character of movement of an arrow of the device (dynamics of indications) are. The scale of the majority of vacuum gauges scaled in mm hg In process of depression increase (and accordingly pressure drop) an instrument reading increases. On each 300 m above sea level absolute indications of the vacuum gauge will differ approximately on 25 mm hg
Attach the vacuum gauge directly to an inlet collector, but not to other apertures through which the vacuum, by the channel of certain length separated from a collector (for example, to apertures before throttle заслонкой is created).
Before the beginning of tests warm up the engine to working temperature. Block wheels and tighten a lay brake. Establish the gear change lever in neutral position (or in position Park on cars with an automatic transmission), start up the engine and leave it to work on frequency of idling.
Before engine start-up carefully check up a condition of blades of the fan of a radiator (absence on them of damages or cracks). In an operating time of the engine do not bring a hand too close to the fan, hold the device on sufficient removal from the fan and do not stand on one line with rotating impeller.
Check up the vacuum gauge indication. On the serviceable engine the vacuum gauge should show depression of 430-560 mm hg, and the arrow of the device should be almost motionless.
The description of character of indications of the vacuum gauge and technique of definition of a condition of the engine on their basis is more low spent.
Too low level of depression usually specifies on негерметичность linings between an inlet collector and throttle knot, a vacuum hose, and also in too later ignition or for the wrong moment of opening and closing of valves. Before removing covers of a gear belt and to check up combination of adjusting labels check up installation of ignition by means of a stroboscope.
If vacuum gauge indications on 75 200 mm hg below normal also are unstable (the arrow twitches) it specifies on негерметичность linings on an input of an inlet collector or in malfunction of an atomizer.
If the arrow regularly deviates on 50–100 mm hg the reason is негерметичность valves. For acknowledgement of this conclusion check up a compression in engine cylinders.
If the arrow irregularly deviates towards low indications or shakes, it specifies in low depression. A plausible reason is the raised resistance to movement of valves or faults in work of cylinders. Check up a compression in cylinders and examine spark plugs.
If idling the arrow quickly fluctuates within 100 mm hg, and engine work is accompanied by a smoke from the muffler then, directing plugs of valves are worn out. For check of it it is necessary to conduct tests of chambers of combustion for tightness (with air rating). If the arrow quickly fluctuates and the increase in frequency of rotation of the engine it is necessary to check up tightness of a lining of an inlet collector and elasticity of springs of valves is simultaneously observed. Such indications also can be caused a burn-out of valves and faults in work of cylinders (ignition failures).
Weak fluctuations of an arrow (within 20–30 mm hg in both parties) specify in unstable work of system of ignition. Check up all provided installations and adjustments, if necessary connect to the engine the analyzer of system of ignition.
At the big fluctuations of an arrow check up a compression in cylinders, or conduct tests for tightness as the idle cylinder or infringement of tightness of a lining of a head of the block of cylinders can be causes of defect.
If instrument readings slowly vary in a wide range check up cleanliness of pipelines of system of compulsory ventilation картера (PCV), correctness of adjustment of a fuel mix, tightness of linings of throttle knot or an inlet collector.
Sharply open throttle заслонку and when frequency of rotation of the engine will reach 2500 mines-1, release заслонку. Заслонка should come back slowly in a starting position. Vacuum gauge indications should fall almost to zero, then increase and exceed the control indications corresponding to work on frequency of rotation of idling, approximately on 125 mm hg then depression should be restored at former level. If depression is restored slowly, and at sharp opening заслонки excess of the control indication is absent, the reason deterioration of piston rings can be. At the slowest restoration of depression check up cleanliness of a final path (as a rule, the muffler or catalytic the converter). The most simple way of such check consists in separation of elements of system of release before a suspicious site and in test repetition.