Honda Acura NSX 1991, Service Manual, Page: 200 / 1420

PGM-FI Control System
. System Description
INPUTS
Sensors
MAP Sensor
TW Sensor
TA Sensor
Throttle Angle Sensor
Oxygen Sensors
Valve Lift Sensor
Vehicle Speed Sensor
Ignition Timing Adjuster
Knock Sensers
A/T Signals
TCS Signals
Starter Signal
Alternator FR Signal
Air Conditioning Signal
A/T Shift Position Signal
M/T Neutral Switch Signal
M/T Clutch Switch Signal
Battery Voltage (IGN. 1)
Fuel Pump Terminal Voltage
VTEC Oil Pressure Switch
Signals
ELECTRONIC CONTROL UNIT
Injector Timing and Duration
Electronic Idle Control
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Other Control Functions
Ignition Timing Control
ECU Back-up Functions
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Injectors
Main Relay (Fuel Pump)
Fuel Pump Relay
Check Engine Light
EACV
A/C Compressor Clutch Relay
Igniter Unit
Purge Cut-Off Solenoid Valve
EGR Control Solenoid Valve
Chamber Volume Control Solenoid Valve
Radiator Fan Relay
Engine Compertment Fan Relay
VTEC Spool Valves
TCS Control Signals
Timing and Duration
The ECU contains memories for the basic discharge durations at various
basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors
to obtain the final discharge duration.
Electronic Air Control
Electronic Air Control Valve (EACV)
When the engine is cold, the is on, the transmission is in gear (A/T only) or the alternator is charging, the ECU
controls current to the EACV to correct idle speed.
Ignition Timing Control
The ECU contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing
is also adjusted for coolant temperature.
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A Knock Control System is also used. When detonation is detected by the knock sensor, the ignition timing is
retarded.
Other Control Functions
1 . Starting Control
When the engine is started, the ECU provides a rich mixture.
2. Fuel Pump Control
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When the ignition switch is initially turned on, the ECU supplies ground to the main relay which supplies current to
the fuel pump for two seconds to pressurize the fuel system.
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When the engine is running, the ECU supplies ground to the main relay which current to the fuel pump.
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When the engine is not running and the ignition is on, the ECU cuts ground to the main relay which cuts current
to the fuel pump.
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Excellent engine performance is achieved through the use of VTEC (Variable Valve Timing and Lift Electronic Con-
trol System), intake manifold chamber control and discharge volume control of the fuel pump.
3. Fuel Cut-off Control
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During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at
speeds over 1,500 rpm.
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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.
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