Fuel injection, basic function

The current air mass/combustion is divided by 14.7 and sent to box 2. The unit is now mg fuel/combustion.

Fig 1: Illustration For Steps 1-8

Courtesy of SAAB-SCANIA OF AMERICA, INC.

In the case of a cold engine, shortly after starting, rapid load changes, knocking or high loads, the current value is multiplied by a compensation factor.

The closed loop value is used as a multiplier. The value is sent to box 4.

Multiply by the value for purge adaptation. The value is sent to box 5.

The multiplicative adaptation value is used as a multiplier and the new value is sent to box 6.

The additive adaptation value is added and the new value is moved to box 7.

If the engine has not yet started, starting fuel is selected. The value is sent to box 8.

The fuel quantity/combustion is the amount of petrol to be supplied to the engine. The value is sent to box 9.

Fig 2: Illustration For Steps 8-13

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Converts the value to the time during which the injector must be open and the new value is sent to box 10.

Injection takes place twice/combustion until the camshaft position has been found. Injection duration is divided by two. The value is sent to box 11.

Adds the injector time delay, which is voltage dependent. The value is sent to box 12.

The value is sent to box 13 unless fuel shut-off is active.

At a determined crankshaft angle, the microprocessor will control the transistor for the injector that is next in the firing order.