21 Aug, 19

Car Engine Running Rich – What Are The Common Symptoms?

When you think about mixtures, whether it’s for a cake or for a chemistry experiment, there will almost always be a set amount of each material needed to create the expected end result. Any deviations from that set amount could result in either a botched up cake or an explosive chemical reaction.


Similarly, the ratio of fuel and air in the engine’s combustion process is referred to as the vehicle’s fuel mixture and there is a certain amount of each element needed for the combustion engine to run smoothly. When there is an issue with the air-fuel ratio, your vehicle can be in either of these states:

  • Running ‘Rich’ – If there is too much fuel being injected into the combustion chamber and there is not enough air, your vehicle will be running ‘rich’.
  • Running ‘Lean’ – When there is more air than fuel, your vehicle will be running ‘lean’.

Essentially, the fuel mixture is controlled by the engine control unit (ECU), through these components: oxygen sensors, emission sensors, fuel injectors, and mass air flow sensors (MAF sensors). In the event that your vehicle is running rich, there are a few signs you will recognise and will alert you that there may be an issue. Below are the top seven reasons your vehicle might be running rich.


The Check Engine Light Is Flashing

Engine MIL Light OnIf there is a flashing check engine light on your dashboard and you use an OBDII scanner to find any trouble codes, it will usually show the diagnostic trouble code P0172. This means that there is too much fuel being injected into the combustion chamber and therefore, more fuel is present in the exhaust gases being released from the exhaust system.


The Engine control unit (ECU) has lots of parts, including an oxygen sensor, the mass airflow sensor and the manifold absolute pressure, which is used to monitor the engine’s air-to-fuel ratio. When a problem is detected by these sensors, they will inform the vehicles ECU and in turn, the engine light will come on to alert the driver.


Pungent Smell

One of the first signs you may notice is a funny kind of smell coming from the exhaust, which can resemble rotten eggs. This will happen when the fuel is not being burned adequately in the combustion engine. This means the extra fuel will be escaping into the exhaust manifold and then it will come out of the tailpipe. The catalytic converter’s job is to burn off any excess exhaust fumes, however, when the fuel mixture is too rich, even it will struggle to burn it all.


Bad Fuel Efficiency

You might notice that you are putting more petrol into your vehicle and not getting as much mileage out of your vehicle than you used to get. This might indicate that your engine is running rich because you are burning more fuel then you need to, for the car to operate properly. In the cold winter months, your vehicle will generally run richer than usual. This means that if your car has a lower MPG (miles per gallon) in the winter than the summer, it is normal.


Engine Performance is Poor

A combination of fuel, air, compression and a spark creates power in the petrol engine – without these components, your engine will not be able to start up or generate any power. Weak engine performance would mean that an issue exists with one of the components.


As we have mentioned, the fuel-air mixture needs to be at the correct ratio for combustion to run smoothly and in turn, for engine performance to be good. If you have low engine power it could mean that there is too much fuel being injected into the combustion chamber or alternatively, too much air and not enough fuel. This could occur, regardless of a working spark or normal compression.


High Carbon Monoxide Emissions

An exhaust pipe naturally removes a specific level of carbon monoxide, but if your engine is running too rich then the levels will be higher than usual. If this is the case, then the vehicle will fail to pass an emissions test when it is being serviced or taken for its MOT test. Too much carbon monoxide is a serious issue and can put your health at risk, especially because it can seep into the car while you are driving. Serious neurological damage could occur to anyone even if they breathed in these fumes for a few minutes.


Rough Idle Engine

A rich fuel mixture could be the reason that your engine is rough idling, and the vehicle will feel rougher and vibrate more when the engine is running. If your engine is running, but your vehicle is stationary and the RPM’s on the tachometer starts to act a little erratic and jump around, there is a problem with your engine running rich. You may also feel your engine running rough when you are driving.


Clogged up or Fouled Parts

There are two symptoms you should be aware of when there is too much fuel in the combustion chamber. Firstly, if your engine is in a ‘rich’ state, your spark plugs may have become carbon-fouled and you can observe this when you look at them, as there will be black, dry soot on the bottom of them. Consequently, this can affect your engine performance.


Furthermore, the purpose of your catalytic converter is to burn any excess fuel before it reaches the tailpipe, therefore, eventually, the converter will become clogged, if your engine has been running rich for a lengthy period of time. Also, the interior honeycomb structure will begin to degrade, which will result in you needing a costly catalytic converter replacement.


How Sinspeed Can Help

Do any of the symptoms above seem familiar and you suspect your engine is running rich? If so, book your vehicle in with Sinspeed today! We can diagnose what is causing the incorrect fuel-air ratio and provide the necessary repairs. Due to your rich engine, if further damage has been caused, such as fouled car spark plugs or you’re experiencing catalytic converter problems, we can offer repair services for these too. Don’t delay, either fill in our easy online form or give us a direct call on 0203 815 9441.

Tags : Air Flow Sensor, Car Engine Running Rich, Engine Light Is Flashing, Fouled Spark Plugs, Idle Engine, Rich Fuel Mixture.
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