Jan 232017

2008 Nissan QashqaiIs this Normal?


This is a perfect example of a properly functioning engine rev limiter.

Rev Limiter

A rev limiter is a device fitted to an internal combustion engine to restrict its maximum rotational speed. Rev limiters are pre-programmed into the car’s Engine Control Unit, except aftermarket units, which are packaged as a separate micro-controller. Cars need a limiter because it prevents the engine from operating above a pre-determined RPM level known as the redline.

Limiters usually work by cutting off a necessary component needed for the combustion processes, although some will change ignition timing. Commonly, rev limiters control the spark or the fuel injectors to the engine.

Types of Control

Spark Control

Ignition Control rev limiting systems work by interrupting the power that is distributed to the spark plugs. Once the car reaches the redline, the engine stops the spark. This is not very common in production cars because it is bad for emissions, as the system still injects fuel into the cylinder and consequently releases unburnt fuel out the exhaust pipe. This type of limiting can also affect the temperatures in the exhaust, causing premature wear on the catalytic converter.

Fuel Control

Fuel-cutting rev limiters are the most common because they are better for emissions, and wear less on engine components. These systems usually start to lean out the engine at redline by cutting fuel to the injectors.

Source: Wikipedia

 Leave a Reply