The air / fuel mixture must be at a perfect ratio of 14.7: 1 to keep the internal combustion engine running smoothly. The engine does not work properly and shows different symptoms when the relationship is disturbed. The car's rich problem arises when too much fuel goes into the combustion chamber. Fuel that is less than the desired level causes a lean car to drive.

Running Rich Vs Lean

The major difference lies in the ratio of the air-fuel mixture. The conditions depend on whether the fuel is more or less than the recommended amount.
What does rich mean? It happens when there is too much gas in the combustion chamber of the engine. What does running mean with leaning? It is
the state in which the combustion chamber does not have enough gas to burn.

It seems that a car that is rich or thin is the two sides of the same coin. The engine computer is mainly responsible for maintaining the right air-fuel mixture. Other components that play a role are the fuel injectors, the emission sensor and the massive air flow sensor.

Symptoms in a car that runs rich and lean

Reaching the perfect ratio - 14.7 parts air to 1 part fuel - is almost impossible for the engine. They usually travel a little rich, especially when they carry a load when the weather is cold and when they accelerate. But it becomes a problem when the fuel becomes too high or too low.

What kind of car leaves you with plenty of symptoms? Do they not differ from the warning signs of a 'lean' problem?

Well, both conditions affect the engine and prevent normal functions. Some of the most common similar symptoms are:

Check that the engine indicator light is on
Loss of engine power
Poor kilometer
Premature engine wear
Engine contamination
Excess CO2 emissions
Premature wear of the emission system
Dirty odor and black smoke from the exhaust
Overheated engine when the car is rich
Draw when the vehicle is running low-fat


Engine Running Rich Reasons

The ideal ratio of air to fuel mixture depends mainly on the amount of fuel in the combustion chamber. Some components, including an oxygen sensor, ECM, and catalyst, are essential for this process. So their fault causes the car to be rich or lean.

Possible reasons why the car is rich:

Oxygen sensor failure
Wrong ECU
Defective mass flow sensor
Dirty / clogged air filter
Blocked open injectors
Defective engine coolant temperature sensor
Retrofitted cooling system

Possible causes for a car that is leaning:

Low fuel
Poor pump controller
Clogged open EGR valve
Defective fuel pressure
Leakage in vacuum

Auto Running Rich: How To Fix It

So, how to repair a rich air fuel mixture or when is it lean? You can use these methods described here to fix a rich mixture problem:

1. Check the air channel flap

The flap inside the air duct is an actuator that acts as an enrichment. It must be partially closed when you start the engine and fully open after the car is heated. If the flap does not work, take the car to a mechanic to repair it.

2. Vacuum lines and hoses

Loose coupled or leaking vacuum lines and hoses can cause the vehicle to be rich. The leak indicates its presence with a hissing sound. But engine noise can dampen it, so you need to be careful.

3. Clean the mass flow sensor

A dirty mass flow sensor can also be a culprit. Remove it from the car and clean with a touch or mass flow cleaner. Reinstall the sensor after cleaning.

4. Acid sensor

If the vacuum lines, the mass flow sensor, and the air channel flap are in good condition, the interference must be with the oxygen sensor. You must replace it with a new one if the existing one is defective.

5. Replace spark plugs

Worn spark plugs can cause this problem. When the plugs cannot create sparks, the gas will not burn properly. As a result, carbon dioxide emissions are high and the engine feels rough. Replacing the plugs is an obvious option. But if this doesn't work, take the car to the service center for tuning.

Conclusion

Doing all of the above will probably correct the problems of the lean mixture. If you have changed one or two sensors, you can do the best car for a few minutes. It allows the engine computer system to get used to the new components and the new volume of air and fuel in the combustion chamber. But if the car still shows symptoms of running thin, take it to a mechanic or dealer. The blinking of the computer and the provision of information on the new air-fuel mixture to the system solves the problem.

Source:
http://www.eliancars.com/2019/02/auto-running-rich-things-you-should-know.html#more
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Kindly check point 4.