Measuring the pressure at the end of cylinder compression can indirectly determine the cylinder's sealing condition. Factors affecting cylinder sealing include the sealing of the cylinder piston assembly, the sealing of the valves and valve seats, and the sealing of the cylinder gasket.

(Cylinder Measurement Tools)

　　1. Testing Tools

　　The cylinder pressure gauge is a specialized tool for measuring cylinder compression pressure, generally composed of a gauge head, a conduit, a one-way valve, and connectors. The cylinder pressure gauge connectors include threaded pipe connectors and tapered or stepped rubber connectors. The threaded pipe connector is used for measuring gasoline engines and can be screwed into the spark plug or injector threaded hole. The rubber connector is used for measuring diesel engines and can be pressed tightly into the spark plug or injector hole. When the one-way valve of the pressure gauge is closed, it can hold the measured cylinder compression pressure reading; when the valve is opened, the gauge needle returns to zero for the next measurement.

　　① The engine should be operated until it reaches normal working temperature: water-cooled engines at 75~95℃ water temperature, air-cooled engines at 80~90℃ oil temperature.

　　② Remove all spark plugs or injectors (for diesel engines).

　　③ Press the tapered rubber connector of the cylinder pressure gauge tightly into the spark plug hole of the cylinder being tested, or screw the threaded pipe connector onto the spark plug hole.

　　④ Use the starter to rotate the crankshaft for 3~5 seconds. After the needle stabilizes, read the value, then press the one-way valve to reset the needle to zero. Each cylinder should be measured at least twice.

　　⑤ Test each cylinder in sequence according to the above method.

　　Tips:

　　① When testing engine cylinder pressure, do not start the engine to avoid damaging the cylinder pressure gauge.

　　② Before testing, for gasoline engines, disconnect the distributor central high-voltage wire or remove the fuel pump relay. For diesel engines, loosen the injector high-pressure oil pipe connector to cut off fuel supply to the cylinder, allowing the engine to operate without ignition.

　　2. Analysis of Test Results

　　After measuring cylinder pressure, judgments are usually made based on the following situations:

　　① If the pressure readings of a cylinder fluctuate significantly over 2~3 measurements, it indicates that the valve sometimes does not close tightly.

　　② If the pressure readings of two adjacent cylinders are low or very low while other cylinders are normal, it is due to leakage in the cylinder gasket between the two adjacent cylinders or loose cylinder head bolts.

　　③ If one or several cylinders have low pressure readings, inject an appropriate amount (generally 20~30mL) of lubricating oil into the spark plug or injector hole, then measure the cylinder compression pressure again and compare the two results. If the second measurement is higher and close to the standard value, it indicates poor cylinder sealing caused by excessive wear of the cylinder, piston rings, piston, or issues such as piston ring misalignment, seizure, breakage, or cylinder wall scratches. If the second measurement is similar to the first, the poor sealing is due to intake/exhaust valves or cylinder gasket leakage.

　　④ If one or several cylinders have high pressure, and the vehicle experiences overheating or knocking during driving, it is due to excessive carbon deposits or changes in compression ratio caused by cylinder bore enlargement after several major repairs.

　　⑤ After major repairs, cylinder pressure should meet the original design specifications: the difference between each cylinder's pressure and the average pressure of all cylinders should be less than 8% for gasoline engines and less than 10% for diesel engines.