What Causes the Fuel Trim System to Run Too Rich?
2 Answers
Fuel trim system running too rich can be caused by the following reasons: 1. High fuel mixture ratio: The engine's fuel mixture ratio is high due to slight leakage of the fuel injector, failure of the water temperature sensor, or possible faults in the air flow meter and oxygen sensor. 2. Insufficient cylinder pressure: The engine's cylinder pressure is insufficient, and the compression ratio is too small. However, this can usually be detected by listening to the engine's performance. If not, measuring the cylinder pressure will help. Additionally, low cylinder pressure is typically a mechanical issue, such as problems with the piston, rings, cylinder, or valves. 3. Weak high-voltage spark: This can be caused by spark plugs with carbon deposits, small gaps, poor performance, or issues like leakage or misfiring.
A rich fuel trim system is generally caused by an imbalance in the air-fuel ratio. When the computer detects that the mixture is too rich, it adjusts the correction value. I've encountered this issue before, and the most common cause is a faulty oxygen sensor. If the sensor is aged or dirty, it can't accurately read the exhaust data, leading the computer to mistakenly inject more fuel. Another reason could be a dirty or obstructed mass airflow sensor, which measures less air, making the computer think the mixture is lean and thus enriching the fuel. Additionally, high fuel pressure due to issues with the fuel pump or pressure regulator can cause excessive fuel injection. Leaking fuel injectors can also directly result in over-fueling. Improper sealing in the intake system might trigger false readings, but these issues should be diagnosed with a scan tool for accurate fault codes. If you notice a sudden increase in fuel consumption or reduced power while driving, be alert and don't delay. Start with simple checks, like cleaning the sensors, and if that doesn't work, take it to a professional shop.
