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Why Your Engine is Running Lean & How To Fix It

Your vehicle’s engine is a rather fickle element. The engine’s air-to-fuel ratio is one of the components that must be precise every time in order to create the power to move your vehicle; if they aren’t, it means your engine could run lean or rich.

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. Learn why your engine is running lean and how to address the issue before it’s too late.

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

While determining the cause of a lean-running engine may be more difficult than one that is running rich, it is vital to locate the cause of the issue. Some symptoms that your vehicle may be exhibiting if your engine is running lean include:

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

Causes of Engines Running Lean

When an engine is starved for fuel, your vehicle will exhibit symptoms that will affect its performance. While you may be able to tolerate some inconsistencies while driving, you shouldn’t ignore the issue 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 a result of a lack of fuel getting to the engine. So, it’s reasonable to assume the trouble may lie with the fuel system. An obstruction in the fuel filter or a failed fuel pump can reduce 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 technician will need to run a series of tests of the fuel system to determine the cause and make repairs.

  • Air Seepage

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

  • Sensors

Any sensor that measures fuel pressure or airflow can result in lean conditions. This includes 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 engine. Failure of any of these sensors will result in your check engine light illuminating. A technician will need 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 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 technician 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 computer will receive inaccurate data, forcing the engine into a lean state. In most cars, if the oxygen sensor malfunctions, it will trigger the check engine light to come on. A technician will need to review the codes stored in the computer that have caused the check engine light to come on. If the oxygen sensor has failed, a replacement should be in order.

Whether your engine is running lean, rich, or giving you some sort of trouble, visit your local Sun Auto Service for a FREE Engine Diagnosis Scan. Our knowledgeable technicians 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 technicians can help with that, too!

Our friendly service advisors 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 one of our many Sun Auto Service locations 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 2-year/24,000-mile nationwide warranty.