ACURA NSX 1991 Service Repair Manual
Manufacturer: ACURA, Model Year: 1991, Model line: NSX, Model: ACURA NSX 1991Pages: 1640, PDF Size: 60.48 MB
Page 1501 of 1640

System Description
Fuel Pressure
The fuel supply system consists of a fuel tank, in-tank high pressure fuel pump, fuel pump relay, fuel pump
resistor, main relay, fuel filter, pressure regulator, injec-
tors and injector resistor.
This system delivers pressure regulated fuel to the in-
jectors and cuts the fuel delivery when the engine is not
running.
Relieving
Do not smoke while working on the fuel system.
Keep open flames or sparks away from the work
area.
Be sure to relieve fuel pressure while the engine is
off.
NOTE: Before disconnecting fuel pipes or hoses,
release pressure from the system by loosening the 6
mm service bolt at top of the fuel filter.
1. Disconnect the battery negative cable from the battery negative terminal.
2. Remove fuel filler cap.
3. Use a box end wrench on the 6 mm service bolt at the fuel filter, while holding the special banjo bolt
with another wrench.
4. Place a rag or shop towel over the 6 mm service bolt.
5. Slowly loosen the 6 mm service bolt one complete
turn.
SERVICE BOLT
12N.m(1.2kg-m. 9 Ib-ft)
SHOP
TOWEL
FUEL FILTER
NOTE:
A fuel pressure gauge can be attached at the 6 mm
service bolt hole.
Always replace the washer between the service bolt
and the special banjo bolt, whenever the service
bolt is loosened to relieve fuel pressure.
Replace all washers whenever the bolts are
removed to disassemble parts.
(cont'd)
ProCarManuals.com
Page 1502 of 1640

Fuel Supply System
Fuel Injectors (cont'd)
Replacement
Do not smoke during the work. Keep open flames away from your work area.
1. Relieve fuel pressure (page 11-87).
2. Remove the intake manifold covers.
3. Disconnect the connectors from the injectors.
4. Disconnect the vacuum hose and fuel return hose from the pressure regulator.
NOTE: Place a rag or shop towel over the hoses before disconnecting them.
5. Disconnect the fuel hose from the fuel pipe.
6. Loosen the retainer nuts on the fuel pipe and harness holder.
7. Disconnect the fuel pipe.
8. Remove the injectors from the intake manifold.
O-RING
Replace.
CUSHION
RING
Replace.
INJECTOR
SEAL
RING
Replace.
9. Slide new cushion rings onto the injectors.
10. Coat new O-rings with clean engine oil and put them on the injectors.
11. Insert the injectors into the fuel pipe first.
12. Coat new seal rings with clean engine oil and press them into the intake manifold.ProCarManuals.com
Page 1503 of 1640

13. Install the injectors and fuel pipe assembly in the manifold.
CAUTION: To prevent damage to the O-ring, install the injectors in the fuel pipe first, then install them in the intake
manifold.
INTAKE MANIFOLD
COVERS
CONNECTOR
FUEL PIPE INSULATOR
MARKINGS
12 N·m
(1.2
kg-m,
9 Ib-ft)
FUEL
PIPES
14. Align the center line on the connector with the mark on the fuel pipe.
15. Install and tighten the retainer nuts.
16. Connect the fuel hose to the fuel pipe. 17. Connect the vacuum hose and fuel return hose to the pressure regulator.
18. Install the connectors on the injectors.
19. Install the intake manifold covers.
20. Turn the ignition switch ON but do not operate the starter. After the fuel pump runs for approximately two seconds, the fuel pressure in the fuel line rises. Repeat this two or three times, then check whether there is any fuel leakage.
FUEL PIPEProCarManuals.com
Page 1504 of 1640

Fuel Supply System
Injector Resistor
Description
The resistor lowers the current supplied to the injectors
to prevent damage to the injector coils. This allows a
faster response time of the injectors.
Testing
1. Disconnect the resistor connector.
2. Check for resistance between each of the resistor
terminals (b, c, d, e, f and g) and the power terminal
(a).
Resistance should be: 5—7
INJECTOR
RESISTOR
MAIN
RELAY
ECU
INJECTOR RESISTOR
INJECTORS
Replace the resistor with a new one if any of the
resistances are outside of the specification.ProCarManuals.com
Page 1505 of 1640

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
Page 1506 of 1640

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
Page 1507 of 1640

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
Page 1508 of 1640

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
Page 1509 of 1640

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
Page 1510 of 1640

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