What does running rich or lean mean?

Almost all motor vehicles run on petrol or diesel fuel and require a mixture of air and fuel in order to burn optimally in the engine. If your vehicle is “running rich”, that means that there is too much fuel and not enough air in your engine. If there is too much air and not enough fuel, then your car is “running lean”.

What’s the big deal?
Both of these conditions can result in poor mileage on your vehicle as well as engine damage if left untreated for an extended period of time. A vehicle running rich will result in the vehicle running hot and will clog up the catalytist resulting in the honeycomb inside it becoming degraded. If the vehicle is running lean, it could resulting in a car that jerks, making your driving experience quite unpleasant.

How do I know?
There are many tell-tale signs as to whether your vehicle is running rich or lean, we have detailed some in a table below:

Running Rich Running Lean
If your exhaust sputters with smoke If your exhaust sputters without smoke
If your exhaust is wet on the inside and smells like fuel Clanking sounds within the engine
Low fuel economy Degraded throttle response
Rich gasoline smells Vehicle jerking while driving

What causes an engine to run rich or lean?

Running too rich could be as a result of:

  • Dirty air filter
  • Stuck open injectors
  • Bad oxygen sensors
  • Faulty ECU
  • Bad Mass Airflow sensor
  • Retrofitted cooling system (Thermostat removed, Fan running direct, double cell radiator)
  • Bad Engine Coolant Temperature (ECT) Sensor

Running lean could be as a result of:

  • Bad fuel pressure
  • Vacuum leak
  • Stuck open EGR valve
  • pump regulator
  • Insufficient fuel

If you think your car is running rich or lean, contact BGA Auto and get it looked at as soon as possible to avoid any long term damage to your engine.