Is Your Engine Running Lean & How To Fix It

Your car’s engine is a complex machine. The cars engines air-to-fuel ratio is one of the components that needs to be precise every time in order to make the power to move your vehicle; if they aren’t, it means your cars engine could run lean or rich.

Learn why your engine is running lean and how to address the issue before it’s too late. A rich-running engine is caused by excess fuel and lack of air, whereas an engine running lean is the exact opposite – the engine lacks enough fuel or there is an excess of air. These conditions can cause trouble down the line, potentially causing knocking or leading to complete engine failure if not resolved.

Symptoms of a Lean Enginehand on a steering wheel of a car

While finding out the cause of a lean-running engine may be more difficult than one that is running rich, it is important to find the cause of the problem. Some symptoms that your car may be exhibiting if your engine is running lean include:

Poor performance
Low power
Start-up trouble
Check engine light on

Causes of Engines Running Lean

When a car engine is starved for fuel, your vehicle will exhibit symptoms that will affect its performance. You may be able to live with some inconsistencies while driving, you shouldn’t ignore the problem as it may result in serious and permanent engine damage. Here are some causes of lean engine conditions and how they can be resolved:

Fuel System Troubles

Lean conditions are caused by a lack of fuel getting to the engine. So, it’s reasonable to assume the trouble may be with the fuel system. An obstruction in the fuel filter or a faulty fuel pump can lower fuel pressure and hinder fuel delivery. Low fuel pressure significantly reduces the rate of flow in the fuel injectors that produces the lean condition. A mechanic will need to run a series of tests of the fuel system to find the the cause and make repairs.

Air Seepage

Vacuum leaks may occur in the intake manifold, where air is pulled in from outside the car. The cause may be related to a leak or weakness within any of the lines or hoses or leaking intake manifold gaskets. A mechanic will preform an air leak performance tests to determine if this is the cause. Once identified, the hose, line, or gaskets will need to be replaced.


Any sensor that measures fuel pressure or airflow can result in lean conditions. Including the intake air temperature sensor, manifold air pressure sensor (MAP), and the EGR (exhaust gas recirculation) sensor. An EGR that is trapped in an open position will mirror the same behaviors as a severe vacuum leak; It allows too much air from the exhaust to haphazardly go back into the car’s engine. Failure of any of these sensors will result in your check engine light illuminating. A mechanic needs to access the computer to view the codes that triggered the check engine light and make repairs or replacements as necessary.

Mass Airflow Sensor (MAF)

Often referred to as the MAF, this sensor monitors and communicates to the car’s internal computer how much air is entering the engine by a wire in the intake system. As air flows by the sensor, the computer calculates how much air is entering the car’s engine. The MAF will begin to fail due to contaminants that build up over time, which alter the computer’s ability to produce the correct calculations. To resolve this issue, a mechanic will clean the mass airflow sensor or replace it based on its condition.

Oxygen Sensor

The oxygen sensor monitors the level of oxygen from the engine’s exhaust. The car’s computer uses this data to regulate how long the fuel injectors need to stay open and how much fuel to release. If the oxygen sensor fails, the car’s computer will receive inaccurate data, forcing the engine run lean. In most cars, if the oxygen sensor fails, it will trigger the check engine light. A mechanic will need to check the codes stored in the car’s computer that have caused the check engine light to come on. If the oxygen sensor has malfunctioned, a replacement should be done.

Whether your vehicle’s engine is running lean, rich, or giving you some sort of problem, our car repair shop for a FREE Engine Diagnosis Scan. Our certified mechanic will scan your on-board computer for diagnostic codes at no charge to you. When further diagnostics or repairs are needed to resolve your engine’s issue, our ASE-certified mechanics can help with that, too!

Our ASE-certified mechanics will guide you throughout the entire process, from your first call to when your car is returned to you. You’ll feel confident in visiting because we’re committed to providing top-quality service and repairs, excellent customer service, and work that is guaranteed in writing and backed by an incredible 1-year/12,000-mile warranty.