1991 ACURA NSX check engine

Fast Idle Thermo Valve

Description

To prevent erratic running when the engine is warming
up, it is necessary to raise the idle speed. The fast idle
thermo valve is controlled by a thermowax plunger.
When the engine is cold, the engine coolant surround-ing the thermowax contracts the plunger, allowing ad-
ditional air to be bypassed into the intake manifold so
that the engine idles faster. When the engine reaches operating temperature, the valve closes, reducing theamount of air bypassing into the manifold.

IAC VALVE

FAST

IDLE

THERMO

VALVE

AIR BYPASS VALVE

WAX
Inspection

NOTE: The fast idle thermo valve is factory adjusted; it
should not be disassembled. 1. Start the engine.
2. Remove the cover of the fast idle thermo valve.
3. Put your finger on the valve seat area and make
sure that there is air flow with the engine cold
(engine coolant temperature below 86°F (30°C)

and idling.)

FAST IDLE THERMO VALVE

If not, replace the fast idle thermo valve and
retest.

12 N.
m

(1.2 kg-m, 9 Ib-ft)

O-RINGS

Replace
4. Warm up the engine (the cooling fan comes on).
5. Check that the valve is completely closed. If not, air suction can be felt in the valve seat area.If any suction is felt, the valve is leaking.
Check engine coolant level and for air in the
engine coolant system. If OK, replace the fast idle thermo valve and recheck.ProCarManuals.com

Idle Control System
Idle Speed Setting
Inspection/Adjustment NOTE: (Canada) Pull the parking brake lever up.
Start the engine, then check that the head lights

are
off.
1. Start the engine and warm it up to normal operating temperature (the cooling fan comes on).
2. Connect a tachometer. Connect a tachometer to loop of ICM second-
ary, or...
TACHOMETER

ICM

Remove the rubber cap from the tachometer
connector and connect a tachometer.
TACHOMETER
TACHOMETER CONNECTOR
RUBBER

CAP
3. Disconnect the 2P connector from the IAC valve.
IAC VALVE
4. Start the engine with the accelerator pedal slightly depressed, then turn the headlights and rear defog-
ger ON. After the MIL comes on, stabilize the

engine speed at 1000 rpm, then slowly release the

pedal until the engine idles.

If the engine stalls, turn the idle adjusting screw
one turn counterclockwise and recheck.
5. Check idling with the headlights and rear defogger
on.

Idle speed should be:
M/T
A/T
550 ± 50 rpm
550 ± 50 rpm (in or range)
Adjust the idle speed, if necessary, by turning
the idle adjusting screw.
If the proper idle speed cannot be achieved,
clean the throttle body port with carburetor
cleaner.

IDLE ADJUSTING

SCREWProCarManuals.com

6. Turn the ignition switch OFF.

7. Reconnect the 2P connector on the IAC valve, then

remove CLOCK fuse in the under-hood fuse/relay

box for 10 seconds to reset ECM.

8. Restart and idle the engine with no-load conditions

in which the headlights, blower fan, rear defogger,

cooling fan, and air conditioner are not operating

for one minute, then check the idle speed.

Idle speed should be:

M/T

A/T
800
50 rpm

750
50 rpm

(in or range)ProCarManuals.com

Fuel Supply System
Fuel Pressure (cont'd)
Inspection 1. Relieve fuel pressure (see page 11-105).
2. Remove the service bolt on the fuel filter while holding the banjo bolt with another wrench and at-
tach the fuel pressure gauge.
3. Start the engine. * Measure the fuel pressure with the engine idling and vacuum hose of the fuel
pressure regulator disconnected from the fuel
pressure regulator and pinched.
4. Reconnect vacuum hose to the fuel pressure regulator.

FUEL
PRESSURE

REGULATOR
FUEL PRESSURE GAUGE

07406–0040001

: If the engine will not start, turn the ignition
switch on, wait for two seconds, turn it off,
then back on again and read the fuel pressure. If the fuel pressure is not as specified, first check the
fuel pump (see page 11-116, 119). If the fuel pump
is OK, check the following:
If the fuel pressure is higher than specified, inspect

for:

Pinched or clogged fuel return hose or piping.
Faulty fuel pressure regulator (see page
11-113).

If the fuel pressure is lower than specified, inspect

for:

Clogged fuel filter.Faulty fuel pressure regulator failure (see page
11-113).

Leakage in the fuel line.ProCarManuals.com

Fuel Pump

Description

Because of its compact impeller design, the fuel pump is installed inside the fuel tank, thereby saving space and simplify-

ing the fuel line system.

FUEL PUMP

FUEL PUMP BRACKET

FUEL FILTER

FUEL PUMP CROSS SECTION (Side view)

RELIEF VALVE
FEUL

PUMP COVER
FUEL PUMP ASSEMBLY CROSS SECTION (Top view)

DISCHARGE PORT

INLET PORT

IMPELLER

CHECK VALVE

ARMATURE COIL
FUEL

PUMP CASING
IMPELLER
GROOVES
CASING

The fuel pump is comprised of a DC motor, a circumference flow pump, a relief valve for protecting the fuel line systems,

a check valve for retaining residual pressure, an inlet port, and a discharge port. The fuel pump assembly consists of the

impeller (driven by the motor), the fuel pump casing (which forms the pumping chamber), and the fuel pump cover.

OPERATION

(1) When the engine is started, the PGM-FI main relay actuates the fuel pump, and the motor turns together with the

impeller.

Differential pressure is generated by the numerous grooves around the impeller.

(2) Fuel entering the inlet port flows inside the motor from the pumping chamber and is forced through the discharge

port via the check valve.

If fuel flow is obstructed at the discharge side of the fuel line, the relief valve will open to bypass the fuel to the inlet

port and prevent excessive fuel pressure.

(3) When the engine stops, the fuel pump stops automatically. However, a check valve closes by spring action to retain

the residual pressure in the line, helping the engine to restart more easily.

(cont'd)ProCarManuals.com

Fuel Supply System

Description

The PGM-FI main relay actually contains two individual
relays.

The relay is located behind the passenger's seat backpanel.
One relay is energized whenever the ignition is on which
supplies the battery voltage to the ECM, power to the
fuel injectors, and power for the second relay.
The second relay is energized for 2 seconds when theignition is switched on, and when the engine is running
which supplies power to the fuel pump.
Relay Testing

NOTE: If the car starts and continues to run, the
PGM-FI main relay is OK.
1. Remove the PGM-FI main relay.
2. Attach the battery positive terminal to the No. 4 terminal and the battery negative terminal to theNo. 8 terminal of the PGM-FI main relay. Then
check for continuity between the No. 5 terminal
and No. 7 terminal of the PGM-FI main relay.
3. Attach the battery positive terminal to the No. 6 terminal and the battery negative terminal to theNo. 2 terminal of the PGM-FI main relay. Then
check that there is continuity between the No. 1
terminal and No. 3 terminal of the PGM-FI main

relay.

FUEL

PUMP

RELAY

FUEL PUMP

RESISTOR

FUEL PUMP
PGM-FI
MAIN RELAY

No. 3
No. 7

No. 8 No. 4

No. 1
No. 6

No. 5 No. 2
TO
IGN.
1

TO BAT

TO
IGN.
1

TO GROUND
TO ST. SWITCH

TO ECM
(A7)
TO ECM
(A25.
CD

TO FUEL PUMP
PGM-FI Main Relay
If there is continuity, go on to step 4.
If there is no continuity, replace the relay and
retest.
4. Attach the battery positive terminal to the No. 3 terminal and battery negative terminal to the No. 8
terminal of the PGM-FI main relay. Then check that
there is continuity of the PGM-FI main relay. Then
check that there is continuity between the No. 5
terminal and No. 7 terminal of the PGM-FI main relay. If there is continuity, the relay is OK;
If the fuel pump still does not work, go to
Harness Testing in the next column. If there is no continuity, replace the relay and
retest. (cont'd) If there is continuity, go on to step 3.
If there is no continuity, replace the relay and
retest.ProCarManuals.com

Fuel Supply System
PGM-FI Main Relay (cont'd)
Troubleshooting Flowchart
(To page 11-123)
BLK/

WHT
GRN/

YEL/
BLK

PGM-FI
MAIN RELAY

BLK/

YEL

BLK

YEL/

BLU

BLK/

YEL

BLK/

YEL
BLK

Engine will not start.
Inspection of PGM-FI main

relay.

Disconnect the PGM-FI main
relay connectors.
Check for continuity between
BLK terminal and body

ground.

Does continuity exist?
Measure the voltage between YEL/BLU terminal and body

ground.

Is there battery voltage?

Turn the ignition switch ON.
Measure the voltage between BLK/YEL terminal and body

ground.

Is there battery voltage?
Measure the voltage between BLK/YEL terminal and body
ground.
Is there battery voltage?
Turn the ignition switch START
position with the clutch pedal
depressed.
Repair open in BLK wire between
the PGM-FI main relay and G101
(located at right middle of
engine).
Replace the ACG(S) (20 A)
fuse in the engine compart-
ment fuse/relay box.
Repair open in YEL/BLU wire
between the PGM-FI main
relay and the ACG(S) (20 A)

fuse.

Replace the No. 2 (15 A) fuse
in the under-dash fuse box.
Repair open in BLK/YEL wire
between the PGM-FI main
relay and the No. 2 (15 A)

fuse.

Replace the IG COIL (30 A)
fuse in the engine compart- ment fuse/relay box.
Repair open in BLK/YEL wire
between the PGM-FI main
relay and the IG COIL (30 A)

fuse.ProCarManuals.com

(From page 11-122)
Connect the test harness be-

tween the ECM and connector.
Disconnect "A" connector from

the ECM only, not the engine

wire harness (see page 11-37).
Measure the voltage between BLK/WHT terminal and body

ground.

Is there battery voltage?
Check for continuity between GRN/BLK terminal and A7 ter-

minal.

Does continuity exist?
Reconnect "A" connector to the
ECM. Reconnect the PGM-FI
main relay.

Turn the ignition switch ON.

Measure the voltage between

A23 (-) terminal and the follow-
ing terminals: A25 (+), C1 (+).

Is there battery voltage?

Turn the ignition switch OFF.
Measure the voltage between A7
(+) terminal and A23 (-) terminal

when the ignition switch is first

turned ON.

Is there 1.0 V or less?
(for 2 seconds)
Replace the PGM-FI main relay. Replace the No. 7 (7.5 A)
fuse in the under-dash fuse
box.

Repair open in BLK/WHT wire
between the PGM-FI main
relay and the No. 7 (7.5 A)
fuse.
Repair open in GRN/BLK wire
between ECM (A7) and PGM-FI
main relay. Repair open in YEL/BLK wire between the ECM (A25,
CD and the PGM-FI main
relay.
Replace the PGM-FI main

relay.

Substitute a known-good ECM
and recheck. If prescribed voltage is now available, replace
the original ECM.

Turn the ignition switch off.ProCarManuals.com