Circuit/System Description

To minimize engine vibrations at idle the engine control module can detect even small variations in engine speed and compensates these variations by adjusting the amount of injected fuel for each cylinder individually. This smooth-running control works only inside calibrated limits. The engine control module calculates the injected fuel quantity in two different ways:

• Fuel quantity based on the time the injector was turned on.
• Fuel quantity based on the increase in crankshaft speed when a specific cylinder fires.

Values that differ too much indicate that the injector is not working properly or that something is mechanically wrong with the cylinder.