What Causes An Engine Run Lean?

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and hhigh pressure gases produced by combustion applies direct force to some component of the engine.

Internal Combustion

Lean burn refers to the use of lean mixtures in an internal combustion engine. There are five factors that could cause a lean mixture to occur.

1. Fuel System

A malfunctioning fuel system can reduce the amount of fuel coming into the engine, causing a run lean condition. A clogged fuel filter can reduce both fuel delivery and fuel pressure. Low fuel pressure will reduce the fuel flow rate at the fuel injectors.

2. Oxygen Sensor

O2 Sensors are used to monitor the amount of oxygen in the engine's exhaust. The on-board computer uses the information from the O2 sensor to make the air/ fuel mixutre richer or leaner. If the oxygen sensor malfunctions, it can send the computer incorrect information about the current state of the exhaust.

3. Air Mass Flow Sensor

The air mass flow sensor monitors and tells the on-board computer how much air is entering the engine. As the air flow into the engine increases, the sensor sends a signal to the on-board computer to increase the amount of fuel being delivered to the engine. If the sensor does not send an accurate signal, the air flow could increase without a corresponding increase in fuel.

4. Computer Malfunction

On-board computers monitor every aspect of the engine's operation - but that doesn't mean that the computer cannot develop problems. Any electronic device can malfunction. The computer could fail to send appropriate fuel delivery signals to the fuel injectors, which would cause the engine to run lean.

5. Air Leaks

Engines have a sea of hoses of various shapes & sizes. These hoses do not last forever. Constant exposure to high heat will eventually cause a hose to deteriorate. If this hose is not replaced, it will cause an air leak. When an air leak occurs, excess air finds its way into the engine.

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