Car Running Rich Explained and 5 Ways To Fix it

When you start your car every day, a series of things take place. The spark plugs ignite the engine, and the pistons and crankshaft begin to move. However, what makes most cars run is either fuel or gasoline.

For this to happen, your car needs to balance the ratio of fuel and air during combustion. A proportion of 14.7:1 is the best ratio. That is 14.7 parts air to 1 part fuel. It is not easy for your car to maintain this ratio. When it fails, and there is too much fuel getting in the engine for combustion, we say your car is running rich.

It means you are spending lots of fuel while driving. To prevent further loss of fuel, car manufacturers use sensors to control the fuel-air mixture. They place sensors on emission points, fuel injectors, and airflows.

Signs that your car is running rich

As long as you are behind the wheels, you and your vehicle should be one. Your car will send you signals that you should interpret accurately.

Check engine light

check engine light

Most cars nowadays have an onboard computer. If the check engine light of your vehicle comes on, it means your engine is running with difficulties. If your motor vehicle has an onboard computer, check for error P0172. This error means your exhaust tailpipe has gases rich in gasoline.

How it works is simple. In your Engine Control Unit (ECU), you will find instruments that collect and record data. The manifold absolute pressure monitors your engine’s fuel-air ratio. Other sensors include oxygen and mass airflow sensors. These sensors feed the ECU with information, and if there is a problem, the check engine light will turn on.

Pungent Smell

You will notice a strong smell coming from your exhaust tailpipe. A smell like rotten eggs. It shows the excess fuel is not getting burnt. The combustion process is not effective as fuel escapes the manifold into the exhaust pipe.

Your car has a catalytic converter that burns off excess fumes. But when the fuel mixture is excessively rich with fuel, there is little it can do to burn off all fumes.

High fuel consumption

You may notice that you are getting reduced gas mileage from your tank than usual. It is an indicator that you are burning more fuel than the car needs. However, it is normal for your car to use more fuel in winter. In cold temperatures, your engine runs a little costly than in warm conditions.

Poor engine performance

The engine is fascinating. It requires only four components to get it running. A combination of air, fuel, compression, and a spark. Weak engine performance can only mean one of these components is underperforming.

If you have a healthy spark and your compression is working fine, then this can mean two things. You have too much air or too much fuel is escaping your engine combustion chamber.

High levels of carbon monoxide emissions

adult driving car from the inside

Your car exhaust pipe produces small levels of Carbon monoxide when it runs. It is normal. And there is a set carbon monoxide emission test for all cars in most states. If your vehicle fails the emission test, it means your vehicle is running rich.

Carbon monoxide is harmful to your health. If it finds its way inside your car with limited air supply, it can affect you neurologically.

Rough idle

Sometimes when your car is idling, your RPM gauge will show erratic readings. Your vehicle will also have unnecessary vibrations. It is often a sign of poor engine performance. It means your car is running rich.

Spark plugs with soot deposits

spark plug with black corrosion

Carbon deposits form on the tail end of your spark plugs when your engine runs rich. The soot will eventually move to other engine parts and damage them. The catalytic converter is sensitive to impurities.

Carbon deposits come from unburnt fuel. The excess fuel has impurities when they enter the catalytic converter. Soon you will have to dismantle it to remove dirt or replace it.

Causes of Engine Running Late

If you suspect your engine is running rich, you should examine if the following devices are faulty.

Faulty Oxygen Sensors

Oxygen sensors are in the exhaust pipe. They detect the air to fuel mixture from the combustion. If the sensors pick an irregular mix, they relay the information to the ECU. The ECU corrects the imbalance in the subsequent engine combustions. A faulty sensor will not do this car will run rich.

Faulty Mass Air Flow Sensor

faulty mass air flow sensor

It is responsible for measuring the air that enters the engine. The sensor determines the amount of air to fuel mixture needed after each combustion. If it is blocked or faulty, your car engine will run rich.

Faulty manifold absolute pressure

Faulty manifold absolute pressure

It is an integral part of your engine. It relays information on the pressure inside the intake manifold. Like most sensors, it wears out with time. When faulty, it transmits incorrect data to the ECU. This action can result in low fuel economy and low engine performance, among other consequences.

Engine coolant temperature sensors

Engine coolant temperature sensors

A cold engine uses more fuel to run well. The engine coolant temperature sensor should measure the engine temperature. Then it determines how much fuel should go into the engine. If this is faulty, then your car will run rich because fuel is not regulated.

Fault in your fuel pressure regulator

This fault usually affects the combustion process and may cause the engine to lose its power. If you want to know if the problem is in the fuel pressure regulator, your car will show the following signs.

  • Your engine misfires and you lose acceleration
  • Fuel leakage
  • Black smoke from your exhaust pipe
  • Fuel leak from your exhaust pipe
  • Spark plugs covered in debris
  • Mileage drop
  • Check engine light
  • Gasoline smell coming from the oil dipstick
  • Fault in your cars intake temperature

If you are wondering when you should change your gasoline then check this article out – How long does gasoline last

When this happens, your car engine may occasionally produce a knocking sound. Or you will notice a drop in your acceleration power. If the temperature sensor is damaged, you should replace it immediately to avoid critical engine complications.

How to fix car running costly complications

The fuel-air mixture is easy to remedy. If you want, you can get to the root cause of the problem. You need to observe the performances of the following devices in your engine. Once you identify the fault, you can remedy before your engine stalls.

Check your car’s air duct flap

Your car’s air duct has a flap that acts as a choke for your engine. When you start your engine, the air duct should be partially open. It fully opens up only when the engine has warmed up. If it does not perform these functions, take your car to the mechanic.

Vacuum hoses and lines

If your vacuum lines are loosely connected, and the hose pipes are leaking, then your car will run rich. If it is a leak, then you will hear a hissing sound. If you suspect a vacuum leak keep your ears open for the hissing sound. Sometimes your engine sound may muffle it.

Cleaning the mass airflow sensor

Mass airflow sensors pick dust overtime. If they get blocked with impurities, they cause your car to run rich. You can clean the sensor yourself and reinstall it when done. It is not complicated to clean it by yourself. You can always call an expert for cleaning.

If cleaning does not work, try replacing the sensor with a new one.

The oxygen sensor

If you have checked the above devices and they show no signs of being defective, then the problem lies in your oxygen sensors. If it is faulty, then you must replace it with a new sensor. It is a sensitive area, and you should probably let your mechanic fix it or replace it.

Change your spark plugs

Worn out sparks plugs do not create sparks. It means that gas will not burn correctly. Therefore, your car’s carbon emission will be high, making your engine feel rough. Changing your plugs may solve this issue. If it doesn’t, then take your vehicle to a servicing shop.


The best way to solve a car running rich problem is to run diagnostics whenever you suspect it. However, the cheapest and effective way remains preventative maintenance. Your vehicle needs regular service and change of worn out moving parts. This way, your car is always running in top condition.

When your car runs rich, it is not alarming if you can accurately identify the cause. As you have seen, there are many reasons why your vehicle can run rich. These are some of the problems you can tackle after you make successful diagnostics. Some require a professional to identify and remedy.

Keeping up with all these signs may be difficult. If so, always have your vehicle manual with you to understand more about your car. To avoid further damage to your vehicle’s engine, only change defective parts that you know.

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