8-VALVE 1.4
ENGINE
FIAT PUNTO TRAINING OUTLINE
Fiat Auto S.p.A.
After Sales Training
4.5.7 Operation during deceleration
Two strategies overlap during this engine utilization phase:
• a transient strategy, to keep the fuel amount supplied to the engine stoichiometric (less
pollution); this phase is recognized by the control unit when the throttle potentiometer
signal shifts from a high voltage value to a lower one
• a strategy for soft “escorting” to a lower engine speed in order to implement the variation
of delivered torque (reduced exhaust brake).
4.5.8 Atmospheric correction
The atmospheric pressure varies depending on the altitude; this causes such a volumetric
efficiency variation that requires a correction of the base ratio (injection time).
The injection time correction will depend on the altitude variation and will be automatically
updated by the electronic control unit every time the engine is switched off and also under
certain throttle position and revs number conditions (typically with low engine speed and
throttle opened to a large extent) (dynamic atmospheric correction adjustment).
Cut-off operation
The cut-off (fuel cut-off) strategy is implemented when the control unit recognizes the
accelerator pedal released position: pedal percent value = 0% and engine speed of more than
approximately 1,350 r.p.m. (this value is approximate and varies depending on a few
parameters, the most significant of which are essentially the temperature and the running
condition).
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The recognition of the accelerator pedal non-released condition and engine speed of less than
1,270 r.p.m. (approximate value varying according to the various models) enables engine feed
again.