Fuel Injection - BOSCH AFC - EUROPEAN Models: Operation

Fuel under pressure from electric fuel pump, flows through a pulsation damper (some models) and fuel filter and is injected into intake manifold branch to mix with incoming air. Surplus fuel returns through a fuel pressure regulator to the fuel tank.

A pressure regulator controls fuel pressure so that a constant difference of 35 psi (2.55 kg/cm² ) exists between fuel pressure and intake manifold vacuum. To aid in cold engine starting, a cold start valve is activated by a thermo-time switch to increase quantity of fuel to be injected.

Each engine cylinder is supplied fuel by an injector. Ignition signal from ignition coil determines frequency of injections while the ECU determines length of each injection.

Air is drawn in through air cleaner and is measured by the airflow meter. Air then travels through throttle chamber and into intake manifold. A throttle valve in the chamber controls air flow while driving. At idle, throttle valve is almost closed and air is drawn through a by-pass port in throttle chamber. Idle speed adjusting screw controls quantity of air intake at idle. During warm-up operation, extra air is by-passed through air regulator to increase engine RPM.

The oxygen sensor, if equipped, detects the amount of oxygen in the exhaust gases. If sensor senses too much or too little oxygen in the exhaust gases, a change in voltage is produced in the sensor and is transmitted to the ECU. The ECU then changes the amount of fuel injected by using the modulating valve to vary the length of time injectors are on. This varying injection time leans or richens the air/fuel ratio, keeping the air/fuel ratio very close to the stoichiometric value of 14.5 to 1.