Understanding EFI Fuel Management
EFI computers have several modes of operation. These modes are determined by the output power needed from the engine's operating conditions:
Closed Loop Mode
The ECU measures teh air/fuel ratio (A/F) from the O2 (or lambda) sensor. THe ECU works to maintain a constance A/F ratio (14.7:1). This ratio is optimal for the catalytic converter to reduce exhaust emisions correctioly. Also, an 14.7 A/F ratio is the ideal sweet spot for the lambda sensor to work accurately, and this gives a good feedback signal.
Open Loop Mode
This differs from closed loop mode as the lambda sensor signal is ignored. The ECU controls the fuel injectors wihtout feedback that the calculated fuel delivery rate matches what the engine receives. Without feedback, the loop is open, there by giving the term "open loop."
Power Enrichment Mode
This only occurs at Widoe Open Throttle (WOT) and is only determined by the Throttle Position Sensor (TPS) from about 60% wot onwards. The ECU in this mode, ignores the lambda sensor and forces a richer A/F ratio than 14.7:1. This is becuase engines develop more power with a slightly richer mix. This is the area that modifiers are most concerned with.
Lean Cruise Mode
This mode can only used be used at light loads when the vehicle speed is above a certain value, for example 100kph cruising. The ECU instructs a leaner A/F ratio, increases spark advance, and occasionally returns to closed loop mode to assess itself.
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