Overfueling

Overfueling is the practice of adding more fuel to an engine than is required by its current operating conditions. This phenomenon can occur in various types of internal combustion engines, including gasoline, diesel, and fuel cell vehicles. The term is distinct from simply topping up a full tank; it refers to the supply of fuel to the intake system that exceeds the needs of the engine’s throttle position, engine load, and air-fuel ratio requirements.

Causes of overfueling include malfunctioning engine control units (ECUs), faulty fuel injectors, clogged air filters, and incorrect sensor readings such as those from the mass air flow sensor or oxygen sensor. In manual engines, a driver’s rapid throttle input or aggressive acceleration can also lead to brief periods of surplus fuel delivery. Overfueling is generally most prevalent in idling or low‑load situations when the engine must compensate for fluctuating air input.

The consequences of overfueling are twofold. First, it reduces fuel economy by unnecessarily consuming additional gallons or liters. Second, the excess fuel can lead to carbon deposits, icing of cold‑air intakes, and increased emissions of unburned hydrocarbons. In extreme cases, a sustained overfueling cycle can damage the catalytic converter or trigger the engine knocking protection system.

Preventive measures involve maintaining proper air‑fuel mixture control, regularly inspecting and cleaning intake components, ensuring accurate sensor calibration, and keeping the ECU firmware up to date. Diagnostics software can detect abnormal fuel pressure or injector timing, helping technicians rectify overfueling before it impacts performance or durability.