Acura NSX 1991 Manual page 229

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PGM-FI System
System Description
3. Fuel Cut-off Control
• During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at
speeds over 1,500 rpm.
• Fuel cut-off action also takes place when engine speed exceeds, 8,300 rpm, regardless of the position of the throttle
valve, to protect the engine from over-revving.
4. A/C Compressor Clutch Relay
When the ECM receives a demand for cooling from the air conditioning system, it delays the compressor from being
energized, and enriches the mixture to assure smooth translation to the A/C mode.
5. Evaporative Emission (EVAP) Purge Control Solenoid Valve
When the engine coolant temperature is below 153°F (67°C), the ECM controls the EVAP purge control solenoid valve
which cuts vacuum to the EVAP purge control canister diaphragm.
6. Intake Air Bypass (IAB) Control Solenoid Valve
When the engine speed is below 4,800 rpm, the IAB control solenoid valve is activated by a signal from the ECM. Intake
air then flows through the smaller chamber, and high torque is delivered. To increase air flow at engine speeds higher
than 4,800 rpm, the solenoid valve is deactivated by the ECM, and the intake air flows through the larger chamber.
7. Exhaust Gas Recirculation (EGR) Control Solenoid Valve
When the EGR is required for control of oxides of nitrogen (NOx) emissions, the ECM supplies ground to the EGR
control solenoid valve which supplies regulated vacuum to the EGR valve.
ECM Fail-safe/Back-up Functions
1. Fail-Safe Function
When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed
valve for that sensor that allows the engine to continue to run.
2. Back-up Function
When an abnormality occurs in the ECM itself, the fuel injectors are controlled by a back-up circuit independent of the
system in order to permit minimal driving.
3. Self-diagnosis Function [Malfunction Indicator Lamp (MIL)]
When an abnormality occurs in a signal from a sensor, the ECM lights the MIL and stores the diagnostic trouble code
in erasable memory. When the ignition is initially turned on, the ECM supplies ground for the MIL for two seconds to
check the MIL bulb condition.
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