What Causes High Cylinder Pressure?
4 Answers
The main reason for excessively high cylinder pressure is excessive carbon buildup in the combustion chamber, which requires cleaning. During engine repair, excessive grinding of the mating surface between the cylinder block and cylinder head can reduce the combustion chamber volume, resulting in an excessively high compression ratio and consequently high cylinder pressure. This issue can be resolved by replacing the cylinder gasket or cylinder head. Below is the method for measuring cylinder pressure using a cylinder pressure gauge: 1. Run the engine until it reaches normal operating temperature; for water-cooled engines, the coolant temperature should be between 75-95°C. 2. Remove all spark plugs or fuel injectors (for diesel engines). 3. Fully open the throttle and choke valves. 4. Press the conical rubber adapter of the cylinder pressure gauge firmly into the spark plug hole of the cylinder being tested, or screw the threaded adapter into the spark plug hole. 5. Use the starter to rotate the crankshaft for 3-5 seconds. Read the measurement once the pointer stabilizes, then press the one-way valve to reset the pointer to zero. Each cylinder should be measured at least twice. 6. Repeat the above steps sequentially for each cylinder.
When I repair cars and encounter high cylinder pressure, it's mostly due to thick carbon buildup in the combustion chamber. The carbon deposits form a hard shell on top of the piston, reducing compression space and naturally causing cylinder pressure to spike. This makes the car shake or produce strange noises when driven. Another common cause is valve timing deviation; if the valves don't seal properly or their opening/closing timing is off, air leaks out, increasing compression force. A malfunctioning cooling system is also problematic—engine overheating leads to expansion, raising cylinder pressure. Poor fuel quality can also cause residue accumulation. During diagnosis, I use a cylinder pressure tester to check data, then inspect valve clearance and piston ring seals. High cylinder pressure can easily lead to knocking, and in severe cases, connecting rod fractures or cylinder head deformation. I always remind car owners to clean carbon deposits regularly and check the coolant and fuel system every six months. This helps avoid major repairs and extends engine life.
My car used to have really high cylinder pressure, and I could feel the engine jerking while driving. Later, I found out it was due to severe carbon buildup. Those black deposits in the combustion chamber took up space, increasing the compression ratio and causing high pressure. Valve issues also made things worse; if they didn't close tightly, air couldn't escape, and cylinder pressure would spike. Insufficient coolant or a broken fan made the engine overheat like an oven, causing parts to expand and increase pressure. I tried using fuel additives to clean the carbon deposits myself, which helped a bit but wasn't enough. Eventually, I had a mechanic check the valve clearance. If high cylinder pressure isn't addressed, not only will the knocking noise get louder, but it could also damage the cylinder walls. Now, I get the intake system cleaned every few tens of thousands of miles, use high-quality fuel, and regularly check the coolant level. Spending a bit on maintenance is better than having to replace the entire engine.
Hey, high cylinder pressure is mostly caused by severe engine carbon buildup. When the combustion chamber is filled with carbon deposits, the compression pressure skyrockets, making the car run unsteadily. Poor valve sealing or timing issues can cause air leaks, increasing cylinder pressure. An inefficient cooling system leading to engine overheating and expansion also contributes to high pressure. Improper fuel can leave residues that accumulate. I recommend checking for carbon deposits first; cleaning them might solve the problem. High cylinder pressure can cause knocking and damage components, so don't delay if issues arise. Using quality fuel and regular maintenance can prevent this.
