5 Symptoms of a Car Engine Running Rich

(Updated on April 22, 2020)

The internal combustion chamber of an engine requires there to be just the right amount of fuel and air mixed together before ignition. The engine control unit is the main computer of the vehicle which oversees all the actions related to the engine. It controls the air flow sensors, emissions sensors, oxygen intake, and fuel injectors. If the computer or any one of these components were to malfunction, it could possibly cause the wrong amount of fuel to be injected into the combustion chamber. In situations where there is too much fuel injected into the chamber and not enough room for oxygen, this would be known as having a “rich fuel mixture.”

The Top 5 Symptoms

A rich fuel mixture in the internal combustion chamber is never a good thing. It will cause a variety of problems for the engine. The symptoms of these problems will be easy to spot if you simply know which ones to look for. Below are the top 5 symptoms that you will experience if you have a rich fuel mixture in your engine.

Need immediate help for your car problem? Chat online with an expert:

Bad Gas Mileage – When you have too much fuel being injected into the combustion chamber, your miles per gallon rate is going to decrease. Then you will find yourself going to the gas station more often to fill up your gas tank. If you want to get your gas mileage to go back to normal, then you have to solve your rich fuel mixture problem.

Check Engine Light – The easiest symptom to spot will be the “Check Engine” light on your dashboard. If this light were to illuminate, it will mean there is some type of issue going on in your engine. It won’t necessarily mean that you have a rich fuel mixture, but that can be one possibility. Look to see if there is an error code that comes up, such as P0172. In many cars, this code indicates that there is too much gasoline in the exhaust gases that are leaving the combustion chamber.

High Emissions – A rich fuel mixture will form an abundance of carbon emissions from your engine. You may notice this problem if you take your car to get an emissions test. If you don’t live in a state which requires one, you should get your emissions tested if you experience any of the other symptoms.

Rough Idle – A rough idling engine can be caused by many things, but a rich fuel mixture is one of them. This symptom will be noticeable because your car will be bouncy as you’re driving. Plus, as the engine runs, there will be a very rough feel to it. Pay attention to the tachometer as you’re driving normally because the needle should be moving all over the place if there is a rough idle problem.

Weak Performance – The balance of fuel and air must be present before they are mixed together and ignited. If you have too much fuel and not enough air, then it will reduce the performance of your engine. You may still get an ignition from the spark and have steady compression, but the overall performance of the vehicle will be worse. You will notice this the most as you’re driving.

Read also: 5 Symptoms of a Bad Diesel Glow Plug in Your Car


A rich fuel mixture is a problem that cannot be postponed for too long. Even if you are able to tolerate a weaker performance and low gas efficiency, think about the components of your engine. An abundance of fuel in the combustion chamber is going to cause these components to get extra hot. If these conditions continue for too long, it could very well cause permanent damage to your engine’s components. Then you will need to spend thousands of dollars to replace them. It is so much easier to just address the fuel abundance problem in the early stages. This will reduce your costs as much as possible.

Leave a Comment