Calculation of Fuel Injection Time

To determine how much fuel has to be injected into each intake manifold, the control module calculates the air mass drawn into each cylinder.

The calculation is performed as follows:
- Three cylinders have sucked in air during one complete engine revolution.
- The control module knows how much air has passed through the mass air flow sensor during one engine revolution.
- The air mass drawn into each cylinder is therefore one-third of the total measured.

The control module keeps the injector open exactly as long as necessary for the correct amount of fuel to be injected in relation to the air mass drawn into the cylinder.

The injection times are corrected by means of the oxygen sensors so that Lambda = 1 is obtained. Lambda control is disengaged under heavy acceleration and full-load enrichment takes place to ensure maximum performance. A richer mixture is obtained when the accelerator is depressed and a leaner mixture when the accelerator is released. Coolant temperature dependent fuel enrichment takes place when the engine is started from cold and during the warm-up period before lambda control is activated.

With a hot engine and normal battery voltage, injection times vary between about 3.0 ms at idling speed and about 18 ms at wide open throttle.