What is Cylinder Pressure?
3 Answers
Cylinder pressure refers to the magnitude of compression force when the piston reaches the top dead center at the end of the compression stroke. Insufficient cylinder pressure indicates reduced cylinder sealing, which will lead to decreased engine power, difficulty in starting, and unstable engine operation if individual cylinders lack sufficient pressure. For gasoline engines, the cylinder pressure typically ranges from 8 to 11 bar, while for diesel engines, it ranges from 12 to 16 bar. Specific values should be referenced according to the manual. Methods for checking the cylinder compression pressure of a gasoline engine: 1. The engine temperature should be between 80-90°C, and the battery discharge level should not be below 50%. 2. Remove all spark plugs and fully open the throttle and choke valves of the carburetor. 3. Press the rubber head of the cylinder pressure gauge firmly into the spark plug hole of the cylinder to be tested and hold it in place. 4. Use the starter to rotate the crankshaft for 3-5 seconds at a speed of 150-180 rpm, and record the pressure value indicated by the gauge. Repeat the measurement twice and check the remaining cylinders in sequence. 5. If the cylinder pressure is below the specified value, add 20-30g of fresh engine oil to the top of the piston and recheck the pressure. If the pressure rises significantly, it indicates severe wear of the piston rings and cylinder. If the pressure remains the same as before, it suggests air leakage at the valves or cylinder gasket, and further inspection is required.
When we drive, cylinder pressure is the air pressure generated inside the engine when compressing air and fuel, which directly affects vehicle starting and power. I feel that when the engine accelerates smoothly, the pressure is within the ideal range; if the pressure is low, the car may have difficulty starting, insufficient power, and increased fuel consumption. Issues like rough cold starts or lack of power when climbing hills may require checking the cylinder pressure. Typically, the pressure value should be within the standard range. If it's too low, it could be due to poor sealing, worn piston rings, or valve problems. Regular maintenance is recommended to avoid major repairs.
In the field of maintenance, I often use a pressure gauge to measure the engine cylinder pressure. The operation is simple: remove the spark plug, connect the specialized gauge, start the engine, and take the reading. Normal values vary by vehicle model; low readings may indicate piston ring leakage, stuck valves, or a blown head gasket. Unstable pressure can lead to incomplete combustion and excessive emissions. After diagnosis, replacing the faulty parts can repair the issue, saving fuel costs and improving engine longevity.
