BMW 3 Series E30

since 1983-1994 release

Repair and operation of the car

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, 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.

Before start of the engine carefully check a condition of blades of the fan (existence on them of damages or cracks). In operating time of the engine you do not bring a hand too close to the fan, you hold the device on sufficient removal from the fan and do not stand on one line with the rotating krylchatka.

Check the indication of the vacuum gage. On the serviceable engine the vacuum gage has to show depression of 430-560 mm Hg, 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.

and. Too low level of depression usually indicates leakage 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.

. 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.

century. If the arrow regularly deviates on 50–100 mm Hg, then leakage of valves is the reason. For confirmation of this conclusion check a compression in engine cylinders.

. 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.

. 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).

e. 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.

. 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.

h. 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.

and. Sharply open a butterfly valve and when turns of the engine reach 2500 about / mines 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.