1991 ACURA NSX air conditioning

Description
Electronic Control System (cont'd)
TRANSMISSION CONTROL MODULE (TCM)

ENGINE
CONTROL
MODULE
(ECM) Shift Control

Lock-up

Control

TCS Control Unit
EPS Control Unit Engine RPM
Air Conditioning Signal Brake Switch Signal
Vehicle Speed Sensor Signal
Mainshaft Speed Sensor Signal
Countershaft Speed Sensor Signal

Self-Diagnosis
Function

Self-Diagnosis Indicator

INTERLOCK
CONTROL UNIT
Lock-up Control Solenoid
Valve B
Lock-up Control Solenoid
Valve A Shift Control Solenoid

Valve B

Shift Control Solenoid
Valve A

Linear Solenoid
Throttle Position
Sensor Signal
Engine Coolant

Temperature
Sensor Signal
Accet Pedal

Angle Signal

Service Check
Connector
ProCarManuals.com

PGM-FI Control System

System Description
INPUTS ELECTRONIC CONTROL UNIT OUTPUTSCRANK/CYL SensorsMAP Sensor
TW Sensor
TA Sensor
Throttle Angle Sensor Oxygen SensorsEGR Valve Lift Sensor
Vehicle Speed Sensor
Ignition Timing Adjuster
Knock Sensers
A/T Fl 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

Injector Timing and Duration
Electronic Idle Control
Other Control Functions Ignition Timing Control
ECU Back-up Functions 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 Compartment Fan Relay
VTEC Spool Valves
TCS Control Signals
Injector Tinning and Duration

The ECU contains memories for the basic discharge durations at various engine speeds and manifold pressures. The

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 A/C compressor is on, the transmission is in gear (A/T only) or the alternator is charging, the ECU
controls current to the EACV to maintain 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.
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
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.

When the engine is running, the ECU supplies ground to the mam relay which supplies current to the fuel pump.

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.
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 During deceleration with the throttle valve closed, current to the 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.ProCarManuals.com

4. A/C Compressor Clutch Relay

When the ECU receives a demand for cooling from the air conditioning system (compressor control unit), it delays

the compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.

5. Purge Cut-off Solenoid Valve

When the coolant temperature is below 70 °C (158 °F), the ECU supplies a ground to the purge cut-off solenoid valve

which cuts vacuum to the purge control valve.

6. Chamber Volume Control Solenoid Valve (CVCSV)

When the engine rpm is below 4,800 rpm the CVCSV is activated by a signal from the ECU, intake air flows through

a smaller chamber, then high torque is delivered. At speeds higher than 4,800 rpm, both solenoid valves are deac-

tivated by the ECU, and intake air flows through the a larger chamber in order to increase airflow.

7. EGR Control Solenoid Valve (EGR CSV)

When the EGR is required for control of oxides of nitrogen (NOx) emissions, the ECU supplies ground to the EGR CSV

which supplies regulated vacuum to the EGR valve.

ECU Back-up Functions

1. Fail-Safe Function

When an abnormality occurs in a signal from a sensor, the ECU ignores that signal and assumes a pre-programmed

value that allows the engine to continue to run.

2. Back-up Function

When an abnormality occurs in the ECU itself, the injectors are controlled by a back-up circuit independent of the

system in order to permit minimal diving.

3. Self-diagnosis Function (Check Engine light)

When an abnormality occurs in a signal from a sensor, the ECU lights the Check Engine light and stores the failure

code in erasable memory. When the ignition is initially turned on, the ECU supplies ground for the Check Engine light

for two seconds.ProCarManuals.com

1. When the idle speed is out of specification and the Check Engine light does not blink CODE 14, check the following
items:Adjust the idle speed (page 11- 84)
Air conditioning signal (page 11-72)
Alternator FR signal (page 11-74)
A/T shift position signal (page 11-76) M/T neutral switch signal (page 11-78)
M/T clutch switch signal (page 11- 80)
Starter switch signal (page 11- 82)
Fast idle valve (page 11- 83)
Hoses and connections
EACV and its mounting O-rings
2. If the above items are normal, substitute a known-good EACV and readjust the idle speed (page 11- 84).
If the
idle
speed
still
cannot
be
adjusted
to
specification (and
the
Check Engine
light
does
not
blink
CODE
14)
after
EACV replacement, substitute a known-good ECU and recheck. If symptom goes away, replace the original ECU.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Air Conditioning Signal
This signals the PGM-FI ECU when there is a demand for cooling from the air conditioning system.

Inspection of Air Condition-

ing Signal.

Connect the ECU test harness

between the ECU and connector.

Disconnect "C" connector from
the engine wire harness only, not

the ECU (page 11-21).

Turn the ignition switch ON.
Measure voltage between C3 (+)

terminal and A26 (-) terminal.

Is there approx. 10 V?
Substitute a known-

good ECU and re-

check. If prescribed

voltage is now avail- able, replace the ori-

ginal ECU.
C3

A26

10 V

Turn the ignition switch OFF. Reconnect "C" connector to the
engine wire harness.
Turn the ignition switch ON.
Momentarily connect A15 ter-
minal to A26 terminal several
times.
Is there a clicking noise from the
A/C compressor clutch? Connect the RED/BLU terminal of

the 4P connector on the A/C

clutch relay to body ground. RED/BLU

A 15

Short
A26

View from UNDER-HOODFUSE/RELAY BOX side

Start the engine.
Is there a clicking noise from the
A/C compressor clutch?
See air conditioner in-

spection (section 22).

Repair open in RED/BLU wire be-

tween ECU (A15) and A/C clutch
relay.

Blower switch ON.
(To page 11-73)ProCarManuals.com

(From page 11-72)
Less than 1 V

C3

A26

A/C switch ON.
Does A/C operate ?

Air conditioning signal is OK.
Is voltage less than 1V?
Measure voltage between C3

( + ) terminal and A26 (-) ter-

minal.

Repair open in BLU/
BLK wire between ECU
(B5) and A/C switch.
Substitute a known-good ECU
and recheck. If symptom/indica-
tion goes away, replace the orig-
inal ECU.ProCarManuals.com