7 Engine Running Rich: Causes and Symptoms (Easy Diagnosis).

The combustion of fuel/air mixture is what powers car engines. The spark plugs provide the ignition spark. The spark will move the crankshaft and pistons.

But inefficiencies could cause fuel to burn more than it is necessary to power the engine. If this occurs, the engine may be running too rich.

Running a car with high fuel consumption means your vehicle is consuming a lot more fuel. It is important to get your engine working as richly as possible.

Is it a sign that an engine is running well?

When a car is running rich, it means the engine is injecting too much fuel and too little air for perfect combustion. Unlucky drivers may experience high fuel bills and costly damage to parts such as the catalyst.

You should take immediate action if you notice that your engine is getting too rich.

Engine running rich: 7 causes

Faulty O2 or MAF sensors are two of the leading causes for engine richness. You can also have it caused by a bad coolant temp sensor, IAT sensors, or a defective fuel pressure regulator.

Because there are so many parts to an engine that can affect fuel mixture, rich engine could result in many things.

This will likely not be enough to fix the problem.

1. Faulty MAF Sensor

The most frequent reason for an engine running high is a bad MAF sensor.

MAF sensors determine how much air is entering an engine. Then, they calculate what proportion of fuel and air should be used. This sensor can fail or become dirty, causing the engine to be too rich or lean. 

The MAF sensor can be faulty and will incorrectly calculate how much air is entering your engine. This could lead to excessive or insufficient fuel being added.

2. Faulty O2 Sensor

For detecting the oxygen-fuel mixture, O2 sensors will be located at the exhaust pipes.

The O2 sensor will inform the engine control unit to increase fuel consumption if it detects a lean mixture.

If this is faulty and telling the engine control module to add more fuel, even if the air-fuel ratio is good – it may cause a rich fuel mixture. An O2 sensor that is defective can make the engine run too rich.

3. Faulty MAP sensor

You may find a car with a MAP sensor rather than a MAF sensor. In some cases, you may have both MAF and MAP sensors.

The MAP sensor determines the amount of air and fuel mixture based upon the pressure inside the intake manifold. If you have a MAP sensor, it’s absolutely worth checking this part.

The diagnostic tool makes it easy to identify the MAP sensor. It can be checked for pressure when the engine is not running. That pressure should match ours.

4. Temperature sensor for engine coolant temperature fault

The engine will not run well if it is too cold. It is the engine coolant temperature sensor‘s job to measure the coolant’s temperature to identify when it should add extra fuel to the engine.

A faulty engine coolant temperature sensor can cause a mixture to be too thick.

5. Faulty Temperature Sensor

Based on the temperature in the intake, the sensor determines whether additional fuel should be added to the engine.

The MAF sensor often includes an intake temperature sensor. It cannot be removed separately.

6. Faulty Fuel Pressure Regulator

Failing fuel pressure regulators can cause fuel pressure to rise or fall too much. The result can be a mixture which is too high or low.

Also, make sure to examine the vacuum line connecting to the fuel pressure regulator for any leaks.

7. Faulty Injector

These injectors regulate the flow of the fuel into the engine. One injector that isn't flowing properly or has become stuck can cause an engine to have a rich mixture.

Engine Running Rich Symptoms

A Check Engine Light on the dashboard is one of the most obvious signs that your engine may be running lean. Another sign could include a large monthly fuel bill and an indicator light that says "Engine Running Rich". Other signs include a black smoke or fuel smell coming out of the exhaust.

These are some of the most common symptoms you need to be aware of, but they're not all. This is a detailed listing of symptoms that indicate an engine that's running smoothly.

1. Check engine light

If the fuel/air ratio exceeds 10%, the engine will light up.

All sensors are controlled by the engine control module. If one sensor fails, the dashboard will display a check engine light.

2. The exhaust smells of fuel

Excess fuel in the combustion chambers means some will not ignite fully if it is too much.

Although the catalytic convert can remove some fuel, excess fuel will be sent to the exhaust. Unburnt fuel smells like rotten eggs.

3. Keep your tank full

A poor fuel economy is one sign that your engine may be running low. The car doesn't need to use all of the fuel it is being provided with. You will spend less on gasoline in winter and when your car is carrying heavy load.

4. Poor engine performance

For your car’s engine performance to be normal, there has to be the right amount of fuel/air mixture. It is assumed that the vehicle will run faster if it has too much fuel. As the fuel that is left over does not burn, this is false.

Low car performance can be caused by problems in the fuel/air ratio. You'll also notice that your RPMs are always moving in an abnormal manner when the car is unattended.

5. Exhaust smoke:

Poor emissions will result from a rich engine. Black smoke will be produced by a rich mixture of fuel and air, which can then leak out through your exhaust pipes.

If it looks by your exhaust pipe like you have a diesel engine, but you don’t – then it is really time to check the air-fuel mixture.

6. Carbon monoxide high content

Carbon monoxide can be a hazardous exhaust gas. Catalytic converters work overtime to eliminate carbon monoxide from the exhaust. When your car’s engine is running rich, it means that you are producing more gas.

Poor ventilation can lead to this dangerous situation. This could also mean that you may not pass state-sanctioned emission tests.

7. No spark plugs

The bottom of your spark plugs will become blackened if you have a rich engine. These deposits can prevent them from working efficiently. Further damage can be caused by the soot getting into other parts of your engine.

Unburnt fuel will eventually find its way into the catalytic convertor, where it will block it due to the high number of impurities. You will eventually have to take it apart and rebuild it.

Engine Running Rich Diagnosis

It is not easy to diagnose an engine running on its own. If you don't want to spend money just on replacing the parts, it is often difficult.

It is the same way that a professional does it. You might also need additional tools.

1. Check for any related codes by connecting an OBD2 scanner. Start diagnosing the problem at that sensor if you discover any additional trouble codes.
2. You can check the O2 sensor live data. Is it indicating that the fuel level is declining all the time? It is likely that this sensor is not to blame.
3. You can connect one of the emission testers or external air fuel meters to check your actual air-fuelmeter. If it shows that the fuel mixture is lean, while the O2 sensor is telling us that the engine is rich and removing fuel – there is a problem with your O2 sensor, and it needs to be replaced.
4. Verify the temperatures of temperature sensors such as air temperature and coolant.
5. Make sure to check the values of any MAF sensors or MAP sensors you may have. If the sensor is defective, replace it.
6. Verify that you have the correct fuel pressure. If the pressure is excessive, check the fuel pressure regulator and the vacuum hose.

Commonly Asked Questions