1991 ACURA NSX Service Repair Manual

Fast Idle Valve
Description
To prevent erratic running when the engine is warming up, it is necessary to raise the idle speed. The fast idle
air bypass valve is controlled by a thermowax plunger.
When the engine is cold, the engine coolant surroun- ding 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 the
amount of air bypassing into the manifold..
Inspection

NOTE: The fast idle valve is factory adjusted; it should

not be disassembled.

1. Start the engine.
2. Remove the cover of the fast idle valve.

3. Put your finger on the valve seat area and make sure
that there is air flow with the engine cold (coolant
temperature below 30°C, 66° F) and idling.

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

FAST

IDLE

VALVE

AIR BYPASS VALVE

12 N·m

(1.2 kg-m, 9 Ib-ft)
O-RINGS
Replace

4. Warm up the engine (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.
Replace the fast idle valve and recheck.

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Idle Control System

Idle Speed Setting

Inspection/Adjustment
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 igniter unit
secondary, or... 3. Disconnect the 2P connector from the EACV.

EACV

TACHOMETER
IGNITER
UNIT

4. Start the engine with the accelerator pedal slightlydepressed, then turn the headlights and rear defog-
ger ON. After the Check Engine light comes on,stabilize the rpm at 1000, 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:
Remove the rubber cap from the tachometer
connector and connect a tachometer.

TACHOMETER

RUBBER

CAP
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

SCREW

TACHOMETER CONNECTORProCarManuals.com

6. Turn the ignition switch OFF.

7. Reconnect the 2P connector on the EACV, then

remove CLOCK fuse in the under-hood fuse/relay

box for 10 seconds to reset ECU.

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:ProCarManuals.com

Fuel Supply System

System Troubleshooting Guide

NOTE: Across each row in the chart, the 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 most likely system

,
etc.

PAGE
89
94
95
97
98
103 106
*
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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)
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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

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

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