Measurement of depression is reliable and rather cheap way of diagnostics of the engine. According to indications of the vacuum gage it is possible to gain an impression about a condition of piston group, about tightness of laying of a head of the block of the cylinders which are soaking up and final collectors, correctness of adjustments of a power supply system of the engine and production of exhaust gases, the capacity of exhaust gases, a condition of valves (their sticking or a burn-out) and springs of valves, and also to check correctness of adjustment of the moment of ignition and preservation of phases of gas distribution during the operation of the engine.

Unfortunately, it is difficult to interpret indications of the vacuum gage and results of the analysis of indications can be wrong therefore, it is expedient to unite vacuum diagnostics with other methods.

Initial factors on which indications of the vacuum gage are analyzed and draw the most exact conclusions about a condition of the engine, absolute instrument reading and the nature of the movement of an arrow of the device (dynamics of indications) are. The scale of the majority of vacuum gages is graduated in mm. рт. column. In process of depression increase (and according to pressure drop) instrument reading increases. On each 300 m above sea level absolute indications of the vacuum gage will differ approximately on 25 mm Hg.

Attach the vacuum gage directly to the soaking-up collector (See a photo), but not to other openings through which vacuum, is created by the channel of a certain length separated from a collector (for example, to openings before a butterfly valve).

Before tests completely warm up the engine. Block wheels and put the car on the emergency brake. At position of the lever of gear shifting in neutral situation (or in situation Park on cars with automatic transmission) start the engine and leave to idle.

Check the indication of the vacuum gage. On the serviceable engine the vacuum gage has to show depression 430 - 560 мм.рттст., and the arrow of the device has to be not mobile almost.

Below the description of character of indications of the vacuum gage and a technique of definition of a condition of the engine on their basis follows.

1. Too low level of depression usually indicates  not tightness of laying between' the soaking-up collector and the camera of a butterfly valve, a vacuum hose, and also too late ignition or for the wrong moment of opening and closing of valves. Before uncovering a gear belt and to check combination of adjusting tags check installation of ignition by means of a stroboscope and remove all other possible causes, being guided by the check techniques described in the present Chapter.

2.  If indications of the vacuum gage    are 75 - 200 mm Hg lower than normal and are unstable (the arrow twitches), then it indicates a leak in laying on an entrance of the soaking-up collector or on malfunction of a nozzle.

3. If the arrow regularly deviates on 50 - 100 mm Hg, then not tightness of valves is the reason. For confirmation of this conclusion check a compression in engine cylinders.

4. The arrow irregularly deviates towards low indications, or shaking shows low depression. The increased resistance to the movement of valves, or interruptions in operation of cylinders is a probable cause. Check a compression in cylinders and examine candles.

5. If idling the arrow quickly fluctuates within 100 mm Hg, and operation of the engine is followed by smoke from the muffler, then the directing plugs of valves are worn-out. For check of this conclusion it is necessary to carry out tests of combustion chambers for tightness (with an air rating). If the arrow quickly fluctuates and  increase in turns of the engine is at the same time observed, then it is necessary to check tightness of laying of the soaking-up collector, elasticity of springs of valves. Such indications can be also caused by a burn-out of valves and interruptions in operation of cylinders (failures of ignition).

6. Weak fluctuations of an arrow (within 20-30 mm Hg in both parties) indicate unstable work of ignition. Check all provided installations and adjustments, if necessary connect the analyzer of system of ignition to the engine.

7.  At big fluctuations of an arrow check a compression in cylinders, or carry out tests for tightness as can be causes of defect the idle cylinder, or violation of tightness of laying of a head of cylinders.

8. If instrument readings slowly change in the wide range, then check purity of pipelines of system of compulsory ventilation of a case, correctness of adjustment of gas mixture, tightness of laying of the case of a butterfly valve, or the soaking-up collector.

9. Sharply open a butterfly valve and when turns of the engine reach 2500 rpm release the gate. The gate has to come back to a starting position slowly. Indications of the vacuum gage have to reduce almost to zero, then increase and exceed the control indications corresponding to stationary idling approximately on 125 mm Hg then depression has to be restored at the previous level. If depression is restored slowly, and at sharp opening of the gate excess of the control indication is absent, then wear of piston rings can be the reason. At extremely slow restoration of depression check purity of a final path (as a rule the muffler or the catalytic converter). The easiest way of such check consists in disconnection of an exhaust path before the suspicious site and in test repetition.

3.6 Use of the rolled compression measuring instrument in comparison with those devices which for ensuring tightness at measurement nestle by hand is more preferable. Make sure that the butterfly valve is enshrined in completely open provision

1. Results of check of a compression in cylinders of the engine allow to judge a condition of group of details in the top part of the engine (pistons, rings, valves and laying of a head of the block of cylinders). Namely, reduction of a compression can be caused by leakage of combustion chambers owing to wear of piston rings, damage of heads of valves and saddles, a progar of laying of a head of the block of cylinders.

2. Begin with the fact that clear sites near spark plugs for what blow compressed air (in the absence of the compressor blow sites automobile, or even bicycle, the pump). It is necessary  to exclude hit of dirt in cylinders at measurement of a compression.

3. Turn out spark plugs (see Gl.1).

4. Completely open a butterfly valve and enshrine in such provision.

5. Disconnect the central high-voltage wire from an ignition distributor cover, connect it to weight on the block of cylinders. For reliability execute connection with weight by means of the special short-circuiting wire piece with clips of alligator type on both ends. Also will not prevent to remove a safety lock of electronic system of injection of fuel on the assembly block that will provide

blackout of the electric fuel pump at measurement of a compression.

6. Insert the compression measuring instrument into an opening for a candle.

7. Include a starter and turn the crankshaft on several turns, monitoring indications of the manometer of the measuring instrument of a compression. On the serviceable engine pressure has to increase quickly. Low pressure after the first piston stroke and slow increase at the subsequent steps of compression indicates wear piston a track. If after the first piston stroke pressure low, and at the subsequent steps of compression does not increase, then leak in valves is the reason or leakage of laying of a head of the block of cylinders [can also be the reason formation of cracks in a head). Decrease in a compression can be also caused by deposits of a deposit on heads of valves. Write down the greatest value of a compression.

8. Repeat the procedure of measurement for other cylinders, compare results to standard data.

9. Through an opening for a candle enter into each cylinder a little oil for the engine (about three full spray butterdishes), then repeat tests.

10. If after oil introduction the compression raised, then it is possible to draw an unambiguous conclusion that piston rings are worn-out. If the compression increases slightly, then leak happens via valves, or laying of a head of the block of cylinders. Leak via valves can be caused by a burn-out of saddles and/or facets of valves, and also deformation of cores of valves, or formation of cracks on them.

11. If the compression equally low only in two next cylinders, then is the most probable cause a laying burn-out between these cylinders. Emergence in combustion chambers or in a case of the crankshaft of the block of cylinders of traces of cooling liquid will be confirmation of this conclusion.

12. If value of a compression in one of cylinders is 20 percent lower, than in other cylinders and the engine unstably idles, then wear of a cam of the cam-shaft operating the final valve can be the cause.

13. If value of a compression exceeds norm, then the combustion chamber is covered with deposits of a deposit. In this case the head of cylinders should be removed and removed a deposit.

14. If the compression in all cylinders low, or strongly differs for different cylinders, then it is necessary to carry out tests of combustion chambers for tightness for what it is necessary to address in a specialized workshop. As a result of tests places of leaks have to be precisely established and the quantitative characteristic of leak is given.

If the decision on dismantle of the engine for carrying out capital repairs, or repair of the main knots was made, then it is necessary to hold certain preparatory activities.

It is extremely important to plan the place in which works will be performed. Undoubtedly, the best place is the workshop. It is very important to have the equipped working platform, and also the place for storage of the car. If there is neither workshop, nor a garage, then also the pure concrete or asphalted platform will be required at least equal.

Washing of a motor compartment and the power unit before dismantle will allow to keep the tool clean and the constant working condition.

Also the floor elevator or a telfer will be necessary. Make sure that these devices have a stock on loading capacity and are capable to lift the engine with transmission. Observance of security measures plays here a paramount role as raising of the engine from the car - operation potentially dangerous.

If works on dismantle of the engine are carried out by the inexperienced person, then the assistant is necessary. Consult and ask to help the persons having experience in such works. There is a set of examples of that as attempts to alone execute dismantle of the engine with raising of the last of a motor compartment came to an end unsuccessfully.

In advance plan the actions. Before beginning works hire or buy all necessary tools and the equipment. To some devices ensuring safety at dismantle and installation of the engine and also

decrease in labor costs the jack cart of sufficient loading capacity, a full set of keys and mandrels, wooden blocks, rags and solvent for cleaning of inevitable pools from the spilled working liquids of the engine belong (besides the elevator). If the elevator is hired, then agree about it in advance, having performed all works in which this mechanism is not required. It will allow to save money and time.

Keep in mind that considerable time you will not be able to use the car. For performance of some works inaccessible in house conditions due to the lack of the special equipment, it is necessary to address in a workshop of car service. These enterprises work according to the schedule and will be expedient to consult there before dismantle of the engine precisely to estimate expenses of time for repair and restoration of details.

Always at dismantle and installation of the power unit be very attentive. Rash actions can be the cause of serious injuries. In advance consider the actions. Do not feel sorry on it for time because the main thing - work without injuries.