Fuel vapour recovery:

the oxygen probe (or "Lambda" probe) informs the control unit of the quantity of oxygen present during exhaust and therefore of the correct air-fuel metering.

The optimal mixture is obtained by the Lambda coefficient = 1 (intake air = thermoetical quantity of air required for combustion). The electrical signal that the probe sends to the control unit undergoes an abrupt variation when the composition of the mixture deviates from lambda = 1. When the mixture is "lean", the control unit increases the quantity of fuel, when the mixture is "rich" the fuel is decreased: in this way the engine functions as near as possible to the ideal lambda value.

The signal from the Lambda probe is processed inside the control unit by an integrator which prevents abrupt swings.

The probe is heated by an electrical resistance in order to be able to to reach the correct operating temperature (approx. 300°C) as quickly as possible.

This probe therefore makes it possible to regulate the supply of fuel to the engine both retroactively and with precision.

This also permits operation within the limits dictated by the laws regarding vehicle emissions.

In addition, this mechanism makes it possible to compensate for altitude as the variations in air density, via the Lambda probe, adjust the delivery by the injectors separately from the air flow meter which detects variations more slowly.

For information regarding the Lambda probe refer to the relative paragraph in this group.

Fuel vapour recovery:

the petrol vapours, originating from the petrol tank are collected in a fuel vapour filter (canister) by the opening of a solenoid valve and are then sent to the intake to be bumed.

This solenoid valve is opened by the control unit only when the petrol vapours are in fact present in the canister and only when the engine is under loading conditions. This makes it possible to to convey the vapours to the engine intake without disturbing the operation of the engine.

The control unit compensates for this extra quantity of petrol with a reduction in the fuel supplied to the injectors. Refer to the relative paragraph in this group for information regarding fuel vapour recovery.

Conection to the air-conditioning compressor:

the control unit is connected to the air conditioning system so that the idle r.p.m. can be adjusted to the increased power which occurs each time the compressor cuts in.

When increased engine performance is requested (hard acceleration), the control unit momentarily interrupts the supply to the compressor (7-10 seconds).

Connection with the Alfa Romeo CODE system:

on cars fitted with the Alfa Romeo CODE system, as soon as the Motronic control unit receives the signal that the key has been turned to MARCIA, it "asks" the above-mentioned system for consent to start the engine: this consent is given only if the Alfa Romeo CODE control unit recognizes the code of the key engaged in the ignition switch as correct.

This dialogue between the control units takes place on diagnosis line K already used for the Alfa Romeo Tester (see specific paragraph).

N.B.: Before doing any work on the system it is advisable to read the corresponding chapter.