What is the method for measuring cylinder pressure?
2 Answers
The method for measuring cylinder pressure is as follows: 1. Run the engine until it reaches normal operating temperature, with coolant temperature between 85-95 degrees; 2. Remove all spark plugs or fuel injectors, and ground the high-voltage wires; 3. Fully depress the throttle to open the throttle valve completely; 4. Press the conical rubber adapter of the cylinder pressure gauge tightly into the spark plug hole of the cylinder being tested, or screw the threaded adapter into the spark plug hole; 5. Crank the starter for 2-3 seconds, read the measurement after the pointer stabilizes, then press the one-way valve to reset the pointer. Perform at least two measurements per cylinder; 6. Additionally, during the second measurement, you can inject a small amount of engine oil (20-30ml) into the spark plug hole before measuring the cylinder pressure again. If the cylinder compression pressure remains the same after oil injection, it can be determined that there is valve leakage.
I've been repairing cars for many years and am used to working with a cylinder compression tester. The car must be warmed up to normal operating temperature first, otherwise the readings won't be accurate. Remove all spark plugs and screw the tester tightly into the spark plug hole. Get an assistant to floor the accelerator or use a remote starter to crank the engine without ignition. Watch the pressure reading pop up on the gauge - you need to test each cylinder thoroughly. Normal readings typically range between 100-150 psi. If any cylinder shows significantly lower pressure (about 20% less than others), it usually indicates worn piston rings or faulty valve seals. Then I often perform a wet test by adding a bit of engine oil and retesting to see if pressure improves - this confirms whether it's ring leakage. If the difference is too large, repairs should be done promptly to prevent more serious engine damage. Basically, even compression readings mean the engine runs well. Don't skip regular testing.
