HFM-SFI quantity control function

S47.00-2500-06

1 Intake manifold

2 Throttle valve

3 Pressure regulator

4 Fuel tank

5 Fuel filter

6 Fuel rail

7 Intermediate flange

A37m18 Fuel pump

Y16 Injector 1

Y17 Injector 2

Y18 Injector 3

Y19 Injector 4

Y65 Injector 5

Y66 Injector 6

A Direction of travel

System overview

The two-stage pump housed in the fuel tank pumps the fuel at a maximum pressure of 4 bar through the fuel filter to the fuel rail. From the fuel rail the fuel flows to the injectors and to the pressure regulator. From there, the excess fuel flows back pressureless into the fuel tank.

Tasks of injected quantity control

- Basic harmonization by means of map

- Start control

- Post-start control

- Warming-up enrichment

- Acceleration enrichment

- Inertia fuel shutoff

- Limiting engine speed

- Lambda control (adaptive subsystem)

Fuel pump relay (K39)

It is actuated by the engine control module as soon as a speed signal is received from the engine. The fuel pump and the heater of the O2 sensor are then operated.

Fuel pressure control

The pressure regulator maintains the pressure difference between fuel pressure and intake manifold vacuum constant in all operating conditions; consequently, the quantity of fuel injected can be determined solely by the opening times of the injectors.

Lambda control

The heated O2 sensor (R22) informs the control module (A52) regarding the residual oxygen contents in the exhaust. The mixture is controlled in the idle speed and part load range on the basis of this signal to lambda = 1 in order to ensure the mixture composition for operation of the catalytic converter.

Depending on the voltage position of the O2 sensor, it signals whether a richer or leaner mixture is required. The change to the air-fuel ratio must not occur suddenly, however, otherwise the vehicle would tend to jerk.

Fuel injection

The injectors (Y16-Y19, Y65-Y66) are operated by the engine control module in line with the firing order. The quantity of fuel injected is controlled by the engine control module by means of the injection period which is defined in line with the operating state.

Fuel injection is performed sequentially, in other words for each cylinder at a defined point in time in line with the firing order.

Variations in the battery voltage which would affect the quantity of fuel injected, are compensated for by the engine control module over the injection time. The injection time is extended by the engine control module for full load and acceleration enrichment.