How to check the compression in the engine? Diagnosis of auto

The serviceability of all units and assemblies is the guarantee of the uninterrupted operation of any car. But if he suddenly began to lose power, or did not even start "hot", then it should be taken to the diagnosis of ICE. During this test, the pressure in the motor cylinders is measured using special equipment. This process is called compression testing. Of course, there is not always an opportunity to turn to professionals in the car service. So today we will look at how to test the compression in the engine on its own.

About compression

In general, this concept denotes the amount of air pressure in the cylinders of an internal combustion engine at the end point of the compression stroke, at the moment the crankshaft rotates by the starter. Diagnosis of the engine VAZ and many other domestic cars on compression makes it possible to more accurately determine the specific problem in the motor. In this case, the engine is not even partially disassembled.

Why does this value decrease over time?

The cause of the pressure decrease in the engine cylinders may be a malfunction of the gas distribution elements. But most often this is due to the natural wear and tear of the mechanisms of the piston group. But anyway, a decrease in pressure significantly affects the engine power and the total fuel consumption.

What else can influence the ICE compression?

In general, there are a lot of reasons for changing the pressure in the cylinders. Among them, the following points should be highlighted:

1. Throttle Position.
2. Wrong clearance in the valve actuator. It should be noted here that a small gap can lead to a later closure, as a result of which the pressure in the cylinders decreases significantly. Also, this can change the value of the angle of rotation of the crankshaft, as a result of which the compression will also significantly decrease.
3. Motor temperature. From this parameter depends the work of many engine elements, in particular, and the same valves. The lower the temperature, the smaller the gap. Accordingly, the pressure in the cylinders also decreases.
4. Various leaks in the details that seal the cavity of the combustion chamber.

Under what conditions of the engine will the compression be ideal? The probability of air leakage through various holes will be minimal only if:

• The cylinder will have an ideally round shape.
• Piston rings fit tightly to each other.
• On the working surface of the cylinder there are no longitudinal risks.
• The gap in the locks of the rings is close to zero.
• Valve plates are closest to the seats.

What is the measurement of the motor compression?

For this there is a special device. It is called a compressometer. At the moment, almost all of its models are equipped with special adapters for different engine models. Compressometer is most often used in "home" conditions, while on professional services for this use more advanced devices - compressors and motor testers.

What kind of malfunctions can be detected using a compressometer?

Using this device at home, you can independently determine a number of faults of the internal combustion engine. For example, if the compression does not increase, this may indicate that there are damages in the valve seats, through which air is vented. If on the scale there is a rapid increase in this value (for example, at the 1st compression stroke, the pressure level is equal to three atmospheres, and then it increases to eight), this indicates the wear of the piston grooves, rings or cylinder walls. When the damper is in the open position and the pressure parameters are changing, there is likely to be a seizure on the surface of the cylinders, or the valves in the engine are deformed. Also it can be coking of rings or a burnout of the valve and the piston. Well, if the data changes with a closed flap, it is worth paying attention to the condition of the walls of the combustion chamber. Cracks can form on it. In addition, the change in compression in this case indicates the "hanging" valves. Still it can be a burnout of a lining of a head of the block of cylinders.

How to check the compression in the engine with your own hands? About the devices

As we said earlier, for this you need to have a special instrument - a compressometer. With it, we measure the pressure level in each cylinder of the engine individually. In total, compressometers are of two types:

1. With threaded tip. For diagnosis, they screw into the candle hole.
2. With clamping lug. Here, the data is measured after the rubber tip is firmly pressed into the hole of the automobile candles.

By the way, the compression in a diesel engine is measured by instruments exclusively with threaded terminals. In addition, such compressometers do not require certain skills and skill in measuring pressure. The diagnostics of the car itself can be carried out both with an assistant, and alone.

Preparing the engine for measurements

Before you start measuring the compression, it is necessary to warm up the engine to operating temperature (not less than 80 degrees Celsius). Also, check the battery charge before use. If it is discharged, be sure to charge it before diagnosis. Another special role in measuring the compression is the serviceability of the starter. When he turns the engine at a frequency of less than 200 rpm, such a diagnosis of the car will simply be useless due to the large difference in the readings. If everything is all right for you, you can start work safely.

Instructions

So, how to check the compression in the engine with your own hands? To begin with, we need to unscrew all the candle wires, then take out all the candles in turn. And they should be decomposed in such a sequence that you can then screw each part into its place. Many motorists ask the question: "Why is it necessary to unscrew all the candles?" The answer to this question is very simple. The point is that checking the compression with twisted candles will not give an accurate result. All values will be only approximate, inaccurate or with large fluctuations. Therefore, in no case should you only twist one spark in the engine.

But back to work. How is the engine compression measured? After the candles for safety reasons, turn off all low-voltage wires from the coils. Further, if you have a carburetor engine and a mechanical type pump, remove the fuel hose. So we will close the supply of fuel to the cylinder. If you have an injector and an electric fuel pump, pull out the device relay or take out the power wires from all the injectors. After these manipulations, you can start measuring.

How to use the compressometer? First, you need to install its end in the candle hole, then press the gas pedal (until the throttle opens ) and start the starter to rotate the engine. So we do until the moment when the data on the scale of the compressor does not stop growing. After that, we record the data in a notebook and necessarily number the cylinder, the pressure in which we just measured. After that, we reset the parameters on the compressometer and move on to the next cylinder. We will diagnose it in the same way.

After the pressure is measured on all the cylinders, we collect all the elements in the reverse order and start analyzing the data.

Analyzing the data

In order to understand how good the result was given by the engine, you need to have an "operation manual" for your model and type of auto. There should be described the normative values of values for this type of engine. Often the normal compression of the VAZ 2107-2170 engine is from 9.5 to 10 atmospheres. In this case, a small spread in the values - up to 1 atmosphere. If the compression in your engine was approximately 8.5-11 atmospheres, this is an excellent indicator. But again, in order to make a more accurate calculation, you need to have a manual and documentation specifically for this engine model.

But if the values you received are below 8.5 atmospheres, then there are faults in the engine, which must be eliminated. In order to identify them, you need 10 milliliters of engine oil. We pour it into the cylinder and repeat it.

If the data obtained has significantly increased and even become an order of magnitude higher than the norm for subsequent measurements in the 2nd, 3rd and 4th cylinders, most likely you have a fault in the piston group. This may be the occurrence or wear of the rings. To eliminate this malfunction, it is necessary to make a full excavation of the engine. Well, if the level of pressure in the cylinders remains the same, then the problem lies in the valves, namely, in their poor fit. Sometimes it happens that the reason for the reduced compression is the burnout of the valves. Most often this happens because of cracks in the piston or a heavily worn gasket cylinder head. This completes the verification of engine compression.

How to find the exact place of failure?

For this we need a compressor. Then follow the instructions. First set the cylinder piston (which we check) to the BMT position. Next, put the car on a handbrake and turn on the 4th gear. After that, we start the compressor and pressurize the cylinder. In this case, you need to carefully look, where exactly there is a leakage of air. If you observe a hissing in the neighboring cylinders, most likely, there was a breakdown of the cylinder head gasket. In this case, it must be replaced. If such a sound was detected in the collector, then the problem is hidden in the inlet or outlet valve. To reveal a breakdown in the engine cooling system, you need to unscrew the expansion tank cap. If faults occur in the antifreeze, bubbles begin to form.

So, we found out how to check the compression in the engine by yourself.