1991 ACURA NSX Service Repair Manual

Pressure Regulator
Description

The fuel pressure regulator maintains a constant fuel
pressure to the injectors. When the difference between
the fuel pressure and manifold pressure exceeds 3.5
kg/cm2 (50 psi), the diaphragm is pushed upward, and

the excess fuel is fed back into the fuel tank through the
return line.

CLOSE
Testing
Do not smoke during the test. Keep
open flames away from your work area.

1. Attach a pressure gauge to the service port of the
fuel filter (page 11-88).
Pressure should be:

323-363
kpa
(3.30-3.70
kg/cm2.
46-53
psi)
(with the regulator vacuum hose disconnected)
PRESSURE FUEL PRESSURE GAUGE
REGULATOR
07406-0040001

INTAKE MANIFOLD

VACUUM

DIAPHRAGM

FUEL
INLET
2. Reconnect the vacuum hose to the pressure
regulator.

OPEN

INTAKE MANIFOLD

VACUUM

DIAPHRAGM

FUEL
INLET
(cont'd)ProCarManuals.com

Fuel Supply System

Pressure Regulator (cont'd)

3. Check that the fuel pressure rises when the vacuum hose from the regulator is disconnected again.
If the fuel pressure did not rise, check to see if it

rises with the fuel return hose lightly pinched.
If the fuel pressure still does not rise, replace the
pressure regulator.
Replacement
Do not smoke while working on fuel sys-

tem . Keep open flame away from work area.
1. Place a shop towel under pressure regulator, then
relieve fuel pressure (page
11-87).
2. Disconnect the vacuum hose and fuel return hose.
3. Remove the two 6 mm retainer bolts.
O-RING
Replace.

PRESSURE REGULATOR

RETURN HOSE
SHOP TOWEL

NOTE:
Replace the O-ring. When assembling the regulator, apply clean engine
oil to the O-ring and assemble it into its proper
position, taking care not to damage the O-ring.ProCarManuals.com

Fuel Filter
Replacement Do not smoke while working on fuel
system. Keep open flame away from work area.

The filter should be replaced: every 4 years or 60,000
miles (96,000 km), whichever comes first or whenever

the fuel pressure drops below the specified value

(323–363
kPa,
3.30–3.70
kg/cm2,
46–53
psi
with

the pressure regulator vacuum hose disconnected) after

making sure that the fuel pump and the pressure

regulator are OK.

1. Place a shop towel under and around the fuel filter.

2. Relieve fuel pressure (page 11-87).
3. Remove the 12 mm banjo bolt and the fuel feed
pipe from the filter.

4. Remove the fuel filter clamp and fuel filter.
5. When assembling, use new washers, as shown.

WASHER
Replace

WASHER
Replace

10 N·m(1.0 kg-m, 7 Ib-ft)
SERVICE BOLT

12 N·m (1.2 kg.m, 9 Ib-ft)
BANJO BOLT28 N·m (2.8 kg-m, 20 Ib-ft)
WASHER
Replace

28 N·m

(2.8
kg-m,

20 Ib-ft)ProCarManuals.com

Fuel Supply System

Fuel Pump

Description

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

fuel line system.

FUEL PUMP

FUEL FILTER
FUEL PUMP BRACKET

FUEL PUMP CROSS SECTION (Side view)
PUMP ASSEMBLY CROSS SECTION (Top view)

DISCHARGE PORT

INLET PORT

RELIEF VALVE
PUMP COVER

IMPELLER

CASING

IMPELLER
GROOVES

PUMP CASING

ARMATURE COIL
CHECK VALVE

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 pump assembly consists of the impeller (driven by

the motor), the pump casing (which forms the pumping chamber), and the pump cover.

OPERATION

(1) When the engine is started, the main relay actuates the 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 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.ProCarManuals.com

Fuel Supply System
Fuel Pump (cont'd)
Testing Do not smoke during the test. Keep open
flame away from your work area.

1. With the ignition switch OFF, disconnect the main
relay connector.
2. Connect a jumper wire between the BLK/YEL wire and BLK/YEL wire .
Replacement
Do not smoke while working on fuel
system. Keep open flames away from your work area.

1. Remove the fuel tank (page 11 -108).

2. Disconnect the connector from the fuel pump.

3. Remove the fuel pump mounting nuts.

4. Remove the fuel pump from the fuel tank.

BLK/YEL
28 N·m (2.8 kg-m, 20 Ib-ft)

6 N·m
(0.6 kg-m,

4 Ib-ft)

BLK/YEL

Jumper wire

FUEL PUMP
FUEL PUMP

BRACKET

3. Relieve fuel pressure as described on page 11-87
then tighten the service bolt.

4. Disconnect the fuel return hose from the regulator.
5. Turn the ignition switch ON for 10 seconds and
measure the amount of fuel flow.

Amount should be: 333 cm3 (11.2 oz) min. in 10 seconds at 12 V

PRESSURE REGULATOR
If fuel flow is less than 333 cm3 (11.2 oz), or


there is no fuel flow, check for:

Clogged fuel filter.

Clogged fuel line.
Pressure regulator failure (page 11-95).ProCarManuals.com

Main Relay

Description

The main relay actually contains two individual relays. This relay is installed behind the passengers seat back
panel.

One relay is energized whenever the ignition is on which
supplies the battery voltage to the ECU, power to the
injectors, and power for the second relay.
The second relay is energized for 2 seconds when the
ignition is switched on, and when the engine is running

which supplies power to the fuel pump.
MAIN RELAY FUEL PUMPRelay Testing
NOTE: If the car starts and continues to run, the main

relay is OK.

1. Remove the main relay.
2. Attach the battery positive terminal to the No. 4 terminal and the battery negative terminal to theNo. 8 terminal of the main relay. Then check for
continuity between the No. 5 terminal and No. 7
terminal of the main relay. If there is continuity, go on to step 3. If there is no continuity, replace the relay and
retest.

No. 7

No. 3
No. 4

No. 8

No. 2

No. 5

No. 6

No. 1

TO
IGN.
1

TO GOUND

TO ST. SWITCH

TO ECU
(A7)
TO BAT

TO ECU
(A25.
CI)

TO FUEL PUMP
3. Attach the battery positive terminal to the No. 6 terminal and the battery negative terminal to theNo. 2 terminal of the main relay. Then check that
there is continuity between the No. 1 terminal and No. 3 terminal of the 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 main relay. Then check that there is
continuity of the main relay. Then check that there

is continuity between the No. 5 terminal and No. 7

terminal of the 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)ProCarManuals.com

Fuel Supply System
Main Relay (cont'd)

Troubleshooting Flowchart
Engine will not start.
Inspection of main relay.
Disconnect the main relay con-
nectors.
Measure the voltage between YEL/BLU terminal and body

ground.

Is there battery voltage? Replace ACG fuse.

Turn the ignition switch ON.

Measure the voltage between BLK/YEL terminal and body

ground.

Replace No. 2 fuse.
Is there battery voltage?
Measure the voltage between BLK/YEL terminal and body

ground.

Is there battery voltage? Replace IG COIL fuse. MAIN RELAY

BLK/

WHT

GRW

BLK

YEL/BLK

BLK/YEL

BLK/YEL
YEL/BLU
BLK

BLK/YEL

Turn the ignition switch START

position with the clutch pedal

depressed.
Measure the voltage between BLK/WHT terminal and body

ground.

Is there battery voltage? Replace No. 7 fuse.
(To page 11-105)ProCarManuals.com

(From page 11-104)
Turn the ignition switch off.
Connect the ECU test harness
between the ECU and connector.
Disconnect "A" connector from
the ECU only, not the main wire
harness (page 11-21).
Check for continuity between GRN/BLK terminal and A7 ter-

minal.

Does continuity exist?
Repair open in GRN/BLK wire

between ECU (A7) and Main

Relay.

battety voltage?

A23
A25

Reconnect "A" connector to the
ECU. Reconnect the main relay.
Turn the ignition switch ON.
Measure the voltage between
A25 (+) terminal and A23 (-) ter-
minal.
Is there battery voltage?

Turn the ignition switch OFF.
Replace main relay.

1V or less

A7
A23

Measure the voltage between A7
(+) terminal and A23 (-) terminal

when the ignition switch is first

turned ON. Is there 1V or less?
(for 2 seconds)
Replace main relay. Substitute a known-good ECU
and recheck. If prescribed
voltage is now available, replace
the original ECU.ProCarManuals.com