Fuel injection, basic function

Fig 1: Illustration For Steps 1-6

Courtesy of SAAB-SCANIA OF AMERICA, INC.

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

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

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

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

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

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

Fig 2: Illustration For Steps 7-10

Courtesy of SAAB-SCANIA OF AMERICA, INC.

More fuel is added if SAI is active.

Starting fuel mass is selected if the engine has not been started.

Fig 3: Illustration For Steps 11-17

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fuel mass/combustion is the fuel mass to be supplied to the engine for each combustion.

Converts fuel mass to nozzle opening duration in ms.

Before the engine has been synchronized, i.e. the camshaft position has been detected by the ignition system, fuel will be injected twice per combustion. The injection duration calculated in block 12 is divided by two.

Voltage dependent needle lift duration is added to the injection duration. This compensates for the delay between the current in the injector coil being activated and the fuel arriving.

Fuel shut-off can come into question under certain conditions, e.g. when engine braking, car immobilized. Injection duration is then zero.

ECM controls the injector that is about to deliver fuel, the sequence depends on the firing order. The crankshaft angle during which injection takes place depends on the prevailing operating conditions.