Checking ignition advance

When the air conditioner is turned on, the engine experiences a speed drop because the compressor takes up power. This involves a drop in rpm, which is particularly evident during idling.

To overcome this condition, ECU, which is informed of the air conditioner «On» signal, arranges to restore nominal speed by increasing the air flow through the step motor.

When the power demand is identified (throttle valve position exceeds a threshold), the ECU inhibits air conditioner operation for a time interval stored in its memory (10 seconds).

CHECKING IGNITION ADVANCE

The ECU also processes the solid state electronic ignition control strategy.

The optimal advance angle is computed as follows:

1. A baseline advance angle is computed using a memory map whose input parameters are engine angular speed of rotation and absolute pressure measured in the inlet manifold. Two different one-dimensional tables are used when idling and under full load according to engine speed.
2. The resulting values are added to the associated coolant temperature correction throughout the entire period when the engine is warming up from cold.
3. The idling table value is further corrected in the case of a sudden drop in idle speed (e.g. due to activation of an appliance).
4. A negative correction is applied in the case of over-run and subsequent cut-off activation.
5. The advance angle is also subject to correction under the following conditions:
   • throttle transit;
   • return from cut-off due to throttle transit;
   • return from cut-off due to minimum rpm threshold.