engine ACURA NSX 1991 Service Repair Manual

PGM-FI System

System Description

INPUTS
ENGINE CONTROL MODULE (ECM)

OUTPUTS

FRONT HO2S

REAR HO2S

MAP Sensor

CKP/CYP Sensor

ECT Sensor

TP Sensor

IAT Sensor

VSS

FRONT KS

REAR KS

Ignition Timing Adjuster

EGR Valve Lift Sensor

A/T Fl Signals

TCS Signals

Starter Signal

ALT FR Signal

Air Conditioning Signal

A/T Gear Position Switch Signal

Neutral Switch Signal (M/T)

Clutch Switch Signal (M/T)

VTEC Pressure Switch

Battery Voltage (IGN.1)

Fuel Pump Terminal Voltage
Fuel Injectors

PGM-FI Main Relay (Fuel Pump)

Malfunction Indicator Lamp

IAC Valve

A/C Compressor Clutch Relay

ICM

EVAP Purge Control Solenoid Valve

Fuel Pump Relay

EGR Control Solenoid Valve

IAB Control Solenoid Valve

Engine Compartment Fan Relay

VTEC Solenoid Valve

TCS Control Signals

FRONT HO2S HEATER

REAR HO2S HEATER

PGM-FI System

The PGM-FI system on this model is a sequential multiport fuel injection system.

Fuel Injector Timing and Duration

The ECM 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.

Idle Air Control

Idle Air Control (IAC) Valve

When the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only) or the alternator (ALT) is charg-

ing, the ECM controls current to the IAC valve to maintain correct idle speed.

Ignition Timing Control

The ECM contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing

is also adjusted for engine coolant temperature.

A knock control system is also used. When detonation is detected by the knock sensor (KS), the ignition timing is

retarded.

Other Control Functions

1. Starting Control

When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration.

2. Fuel Pump Control

When the ignition switch is initially turned on, the ECM supplies ground to the PGM-FI main relay that supplies

current to the fuel pump for two seconds to pressurize the fuel system.

When the engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.

When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay which cuts

current to the fuel pump.

Excellent engine performance is achieved through the use of VTEC (Variable Valve Timing and Valve Lift Electron-

ic Control System), intake air bypass control and discharge volume control of the fuel pump.ProCarManuals.com

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 1 58 °F (70°C) the ECM supplies a ground to the EVAP purge control

solenoid valve which cuts vacuum to the EVAP purge control diaphragm valve.

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 hight 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 in, the ECM supplies ground for the MIL for two seconds

to check the MIL bulb condition.ProCarManuals.com

PGM-FI System
Troubleshooting Flowchart Engine Will Not Start
Engine will not start.
Watch the Malfunction Indicator
Lamp (MIL) and turn the ignition

switch ON.

Did the MIL come on at all?Did the MIL go off after
two seconds?

Turn the ignition switch OFF.

Connect the test harness between
the ECM and connectors (see page 11-37).

Turn the ignition switch ON.

Measure voltage between body

ground and the following termi-
nals individually: A23, A24.

Is there less than 1.0 V?

Inspect fuel pressure (see page
11-106).

Is fuel pressure OK?
Perform ignition system check (see section 23
).
Perform troubleshooting on page

11-43.

Perform troubleshooting on page
11-44.

Repair open in wire between ECM

and G101 (located at right middle

of engine) on wire that more than
1.0 V.

Repair as necessary.ProCarManuals.com

Troubleshooting Flowchart

Engine Control Module (ECM)
Malfunction Indicator Lamp (MIL)
never comes on (even for two se-
conds) after ignition is turned on.
Is the low oil pressure light on?

Turn the ignition switch OFF.

Connect the test harness between
the ECM and connectors (see page 11-37).
Connect A13 terminal to body
ground.

Turn the ignition switch ON.
Is the MIL on?

Measure voltage between body
ground and the following termi-
Is there less than 1.0 V?
Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the origi-

nal
ECM. Inspect No. 5 (10 A) fuse in the
under-dash fuse box.
Is the fuse OK?
Repair open in YEL wire between
No. 5 (10 A) fuse and gauge as-

sembly.

Replace the MIL bulb.
Repair open in BLU wire be-
tween ECM (A13) and gauge

assembly.

Repair open in wire between ECM
and G101 (located at right middle of engine) that had more than 1.0

V.
Replace the fuse.
G101
(cont'd)

nals individually:

A23,
A24,

A26,
B2.ProCarManuals.com

PGM-FI System

Troubleshooting Flowchart
Engine Control Module (ECM) (cont'd)
Malfunction Indicator Lamp (MIL) stays on after two seconds.

Turn the ignition switch ON.

Connect the service check con-

nector terminals with a jumper

wire.
Does the MIL indicate
any Diagnostic Trouble

Code (DTC)?

Remove the jumper wire from the
service check connector.
Try to start the engine.Did the engine start?
Remove and inspect the ACG (S) (20 A) fuse in the engine compart-
ment fuse/relay box.
Is the fuse OK?
(To page 11-45) Go to self-diagnostic procedures
(see page 11-34).

Turn the ignition switch OFF.

Connect the test harness between

the ECM and connectors (see page 11-37).

Turn the ignition switch ON.
Measure voltage between C9 (+)

terminal and D22 (-) terminal.

Is there approx. 5V (A/T: 11 V)?
Repair short to body ground in
BLU wire between the ECM (C9),
TCM, EPS control unit, ABS con-
trol unit or TCS control unit and service check connector.
Repair open in BLU wire be-
tween ECM (C9) and service check connector.
Repair open in GRN/WHT wire
between service check con-
nector and ECM (D22).
Replace the fuse.
NOTE: After repair, disconnect the service check con-
nector jumper wire, test drive the car, and recheck the
MIL for a code. NOTE: When there is no code stored, the MIL will stay
on if the service check connector is jumped.
Connect the service
check connector termi-

nals with a jumper wire.

Measure voltage be-

tween C9 (+) terminal

and D22 (-) terminal.

Is there approx. 5 V(A/T:
11 V)?

Remove the jumper
wire from the service
check connector.
(To page 11-45)ProCarManuals.com

(From page 11 -44)
Inspect the IG COIL (30 A) fuse

in the engine compartment

fuse/relay box.
Is the fuse OK?

Turn the ignition switch ON.
Disconnect the 3P connector of
each sensor one at a time: MAP sensor

EGR
valve
lift
sensor
Accelerator pedal angle sensor
Does the MIL remain ON?
Connect the service check con-

nector terminals with a jumper

wire.
Disconnect the 3P connector of

each sensor one at a time:
TP sensor
Ignition timing adjuster

Does the MIL indicate
code 7 or 18?

Turn the ignition switch OFF.
Remove the jumper wire from the
service check connector.
Connect the test harness.

Disconnect the "D" connector

from the ECM only, not the engine

wire harness (see page 11-37).

Check for continuity between

body ground and the following

terminals: D19, D20.

(To page 11-46) Replace the fuse.
Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the origi-
nal
ECM.
Replace the sensor that caused
the light to go out upon its discon- nection.
Replace the TP sensor or ignition
timing adjuster. (From page 11-44)

Turn the ignition switch
OFF.

Disconnect "A" con-
nector from the ECM.

Turn the ignition switch

ON.
Is the MIL on?

Repair short to body
ground in BLU wire be-

tween the ECM (A13)
and
MIL.

Continuity?

(cont'd)ProCarManuals.com

PGM-FI System
Troubleshooting Flowchart Engine Control Module (ECM) (cont'd)
(From page 11-45)

Is there continuity?

Reconnect all the connectors. Reconnect the "D" connector to

the
ECM.

Turn the ignition switch ON.

Measure voltage between body

ground and the following termi-

nals individually:
A26,
B2.

Is there less than 1.0 V?
Measure voltage between A26
(-) and the following: C1 (+) and

A25 ( + ).

Is there battery voltage?

Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the origi-

nal
ECM. Repair short to body ground in
YEL/WHT wire between ECM
(D19) and MAP sensor.
Repair short to body ground in
YEL/WHT wire between ECM
(O20) and TP sensor. EGR
valve life sensor, ignition tim-
ing adjuster or accelerator pe-
dal angle sensor.
Repair open in BRN/BLK (A26) or
BRN/WHT (B2) and G101 (locat-
ed at right middle of engine).
Repair open in YEL/BLK wire
between ECM (A25. CD and
PGM-FI main relay.
Check PGM-FI main relay and
wiring connectors at PGM-FI
main relay.ProCarManuals.com

Idle Control System

System Troubleshooting Guide

NOTE:
Across each row in the chart, the sub-systems that could be sources of a symptom are ranked in the order they should
be inspected, starting with . Find the symptom in the left column, read across to the most likely source, then refer to

the page listed at the top of that column. If inspection shows the system is OK, try the next system , etc.

If the idle speed is out of specification and the Malfunction Indicator Lamp (MIL) does not blink code 14, go to inspec-

tion described on page 11-88.

PAGE
SUB-SYSTEM

SYMPTOM
DIFFICULT TO START
ENGINE WHEN COLD
WHEN COLD FAST IDLE OUT OF
SPEC
(1,000-2,000
rpm)
ROUGH IDLE
WHEN WARM RPM TOO HIGH
Idle speed is

below specified
rpm (no load)
Idle speed does
not increase after
initial start up.

WHEN WARM
RPM

TOO LOW
On models with

A/T, the idle

speed drops in gear

Idle speeds drops

when air

conditioner in ON or

OFF

Idle speed

fluctuates with

electrical load
WHILE
WARMING UP

FREQUENT
STALLING

AFTER
WARMING UP
FAILS EMISSION TEST
IDLE

ADJUST-

ING

SCREW
IDLE AIR

CONTROL
VALVE
AIR

CONDI-

TIONING
SIGNAL
ALTER-

NATOR
FR

SIGNAL
NEUTRAL

SWITCH

SIGNAL
(M/T)
STARTER

SWITCH
SIGNAL
FAST

IDLE

THERMO
VALVE
HOSES

AND

CONNEC-
TIONS

CLUTCH

SWITCH

SIGNAL
(M/T)

AUTOMATIC

TRANSAXLE
GEAR

POSITION
SIGNAL

102

88

90

92


94

96

98


100


101ProCarManuals.com

System Description

The idle speed of the engine is controlled by the Idle Air Control (IAC) valve.

The valve changes the amount of air bypassing into the intake manifold in response to electric current controlled by the

ECM.

When the IAC valve is activated, the valve opens to maintain the proper idle speed.

(cont'd)
IDLE

ADJUSTING

SCREW

FAST

IDLE

THERMO

VALVE
IAC VALVE

TO PGM-FI MAIN

RELAY
YEL/BLK
BLU/REDProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Air Conditioning Signal

This signals the ECM when there is a demand for cooling from the air conditioning system.

Inspection of Air Condition-

ing Signal.
Connect the test harness be-
tween the ECM and connector. Disconnect "C" connector from
the engine wire harness only, not
the ECM (see page 11-37).
Turn the ignition switch ON.
Measure voltage between C3 (+)

terminal and A26 (-) terminal.

Is there approx. 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?

Start the engine.

Blower switch ON.
(To page 11-91) Repair open in RED/BLU wire be-
tween ECM (A15) and A/C
clutch relay. 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. View from relay side
(sub relay box A)

RED/BLU

See air conditioner in-
spection (see section
22).
Substitute a known-
good ECM and re-
check. If prescribed
voltage is now avail-
able, replace the ori-
ginal ECM.ProCarManuals.com