An engine that is running lean is one that is not receiving enough fuel. 

If your engine is receiving lots of air and little fuel, it means the air-to-fuel mixture is too light. 

A motorist notices the engine is running lean when some signs begin to manifest. 

According to James Mugaga, a mechanic, when the engine starts vibrating, it is a sign it is receiving little fuel compared to the air it needs to operate effectively, hence running lean.

Bad performance in the sense that your vehicle will cut down on power because the vehicle’s system is receiving less fuel for it to generate enough power to function effectively.

And because of the above, the engine might struggle to start because the fuel-to-air mixture cannot support combustion. You might have problems keeping the vehicle going when it starts.

What causes engines to run lean?

Fuel filter 

Charles Semukuutu of Victoria Motors Limited says a clogged fuel filter can make an engine run lean but can also present other complications like misfiring. 

“Because you have multiple cylinders, fuel distribution is not the same. If you have four cylinders, fuel supply comes from the left or right side of the engine. You might find the one that receives first or last receives the most. That leads to misfiring,” he explains, adding that the clogging means fuel pressure gets compromised.

Mugaga notes that a clogged fuel filter is one of the reasons an engine might run lean; because it cleans up all the dirt in the fuel, it gets dirty with time to the point it can’t perform its function.

The fuel injectors 

These are valves charged with getting fuel into the engine’s combustion chamber. They might also be dirty forcing the engine to run lean. 

They are delicate that they don’t soldier on for long after encountering dirt; a little dirt can stop them from working. As much as they can be cleaned, most times they will call for replacement.

The fuel pump 

When faulty, this will not let enough fuel into the combustion chamber because of the inability to fetch enough from the fuel tank. 

Therefore, the fuel-to-air ratio will not balance forcing the engine to struggle with lots of air and little fuel, hence running lean. 

However, Semukuutu says mechanically, the chances of an engine running lean because of a faulty fuel pump is low.

Oxygen sensor

Semukuutu says an engine can run lean when the vehicle is in high gears because when the oxygen sensor is not on, the control unit does not get a report on how to regulate the fuel mixture so they vehicle operates like it should. 

Remember when there is too much oxygen compared to fuel, the engine loses power.