What is the reason for excessive oil in the combustion system of the first exhaust cylinder in a Focus?
3 Answers
Ford Focus cylinder combustion system excessive oil may be caused by incomplete engine combustion, requiring inspection and cleaning of engine carbon deposits to improve combustion efficiency. Below is extended information on cylinders: 1. Single-acting cylinder: Only one end has a piston rod, with air supplied from one side of the piston to generate pressure, which pushes the piston to extend, returning via spring or gravity; 2. Double-acting cylinder: Alternating air supply from both sides of the piston, outputting force in one or two directions; 3. Diaphragm cylinder: Uses a diaphragm instead of a piston, outputting force in one direction only, reset by spring. It has good sealing performance but short stroke; 4. Impact cylinder: A new type of component that converts compressed gas pressure energy into high-speed (10-20 m/s) kinetic energy of the piston for work. The impact cylinder adds a cover with a nozzle and drain port.
I've repaired many Focus models, and there are quite a few common reasons for excessive oil in the first exhaust cylinder. A leaking fuel injector is the prime suspect—if oil keeps leaking in, of course, the level will rise. Sensors can also malfunction; for example, a faulty oxygen sensor might falsely report low air levels, forcing the engine to inject more fuel. A malfunctioning mass air flow sensor can miscalculate the air intake, also leading to excessive fuel injection. An ECU programming error could also be to blame—if it sends wrong commands, fuel injection becomes uncontrolled. Worn piston rings or poor cylinder sealing can allow engine oil to mix in, causing the combustion chamber to smoke from excess oil. Additionally, if the fuel pressure regulator gets stuck, fuel pressure rises too high, naturally leading to over-injection. These issues can range from increased fuel consumption and excessive emissions to spark plug carbon buildup and engine knocking. I once saw a case where replacing the fuel injectors and sensors solved the problem. Regular maintenance should include cleaning the fuel system and timely sensor replacements—don’t wait until the problem worsens. Ignoring this issue will eventually leave the car stranded, so I recommend professional diagnosis at a specialized shop.
My old Focus had this issue before, where the first cylinder had excessive fuel, which was quite annoying. The reason could be dirty or clogged fuel injectors, causing them to leak and spray too much fuel. Another possibility is an ECU misconfiguration, where the car forcibly injects excessive fuel, leading to incomplete combustion. If the air filter hasn't been replaced and is clogged, insufficient airflow can trick the computer into injecting extra fuel. I once tried to save money by not replacing the filter, and it resulted in excessive fuel in the cylinder and black smoke. A faulty oxygen sensor is even worse—it sends incorrect signals, forcing the engine to dump excessive fuel. Additionally, issues with the fuel pump or fuel lines, such as high pressure, can also cause this. I remember the car shaking badly with skyrocketing fuel consumption, and later diagnostics revealed a sensor malfunction—it only stabilized after repairs. Ignoring these minor issues can lead to severe carbon buildup in the engine over time, making the car sluggish and costly to run. The key is early diagnosis and repair—don’t wait until it won’t start to fix it.
