How to Measure Cylinder Pressure?
2 Answers
To measure cylinder pressure, follow these steps: 1. Use compressed air to clean the dirt around the spark plugs, then remove all spark plugs. For gasoline engines, also disconnect the ignition system's secondary high-voltage wires and securely ground them to prevent electric shock or fire. 2. Insert the conical rubber tip of the dedicated cylinder pressure gauge into the spark plug hole of the cylinder being measured, ensuring it is properly aligned and tightly sealed. 3. Fully open the throttle (and the choke if equipped), then use the starter to rotate the crankshaft for 3 to 5 seconds (at least 4 compression strokes). Stop rotating once the pressure gauge needle indicates and maintains the maximum pressure reading. 4. Remove the pressure gauge, record the reading, and press the one-way valve to reset the gauge to zero. Repeat this process for each cylinder, measuring each cylinder at least twice. Calculate the arithmetic mean of the measurements for each cylinder and compare the results with standard values to analyze and assess the cylinder's working condition.
My last experience measuring cylinder pressure myself left a deep impression. You need to prepare a dedicated cylinder pressure gauge, wait for the engine to completely cool down, and remove all spark plugs to avoid damaging components. Before testing, disconnect the ignition coil plug or remove the fuel injector fuse to prevent fuel injection during cranking. Locate the correct spark plug hole and connect the pressure gauge head, ensuring it's tightly screwed to prevent air leaks. Have an assistant fully depress the accelerator pedal to keep the throttle wide open. Then crank the starter for about 5 seconds until the pressure gauge needle stabilizes at the maximum reading. I've tested many vehicles - normal cylinder pressure typically ranges between 980kPa to 1270kPa, with adjacent cylinders showing no more than 10% difference. If you encounter significantly low readings, add a few drops of oil into the cylinder and retest. If the reading improves, it indicates piston ring issues; no change suggests valve sealing problems. Remember to test every cylinder - only by comparing data can you identify the true fault.
