1991 ACURA NSX Service Repair Manual

Emission Control System

Catalytic Converter

Description

The 3-way catalytic converter is used to convert hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) in the
exhaust gas, to carbon dioxide (CO2), dinitrogen (N2) and water vapor.

HOUSING

CATALYSTProCarManuals.com

Inspection
If excessive exhaust system back-pressure is suspected, remove the catalytic converter from the car and make a visual

check for plugging, melting or cracking of the catalyst. Replace the catalytic converter if any of the visible area is damag-

ed or plugged.

HEAT SHIELD

GASKET
Replace.

34 N·m
(3.4 kg-m,

25 Ib-ft) 34 N·m (3.4 kg-m, 25 Ib-ft)
HEAT SHIELD 10 N·m (1.0 kg-m, 7 Ib-ft)
HEAT SHIELDFRONT
CATALYTIC

CONVERTER

Removal/Installation, Section 9

Inspect housing for cracks or

other damage.
Inspect element for clogging by
looking through the inside.

FRONT OF
VEHICLE

GASKET
Replace.
34 N·m
(3.4 kg-m,

25 Ib-ft)

REAR

CATALYTIC
CONVERTER
Removal/Installation, Section 9
Inspect housing for cracks or
other damage.
Inspect element for clogging by
looking through the inside.

34 N·m (3.4 kg-m, 25 Ib-ft)
10 N·m (1.0 kg-m, 7 Ib-ft)
HEAT SHIELDProCarManuals.com

Emission Control System
Positive Crankcase Ventilation System
Description The Positive Crankcase Ventilation (PCV) system is
designed to prevent blow-by gas from escaping to theatmosphere. The PCV valve contains a spring-loaded

plunger. When the engine starts, the plunger in the PCV
valve is lifted in proportion to intake manifold vacuum and
the blow-by gas is drawn directly into the intake manifold.

PCV HOSE
BLOW-BY VAPOR
FRESH AIR
PCV VALVE
Inspection
1 Check the crankcase ventilation hoses and connec- tions for leaks and clogging.

BREATHER

PIPE

2. At idle, make sure there is a clicking sound from the PCV valve when the hose between PCV valve and

intake manifold in lightly pinched with your fingers or

pliers.
If there is no clicking sound, check the PCV valve
grommet for cracks or damage. If the grommet is
OK, replace the PCV valve and recheck.

PCV VALVE
PCV HOSE
Gently pinch here
BREATHER HOSE
FRONT OF
VEHICLEProCarManuals.com

Evaporative Emission Controls

Description

The evaporative controls are designed to minimize the amount of fuel vapor escaping to the atmosphere. The system consists of

the following components:

A. Charcoal Canister

A canister for the temporary storage of fuel vapor until the fuel vapor can be purged from the canister into the engine and

burned.

B. Vapor Purge Control System

Canister purging is accomplished by drawing fresh air through the canister and into a port on the throttle body. The

purging vacuum is controlled by the purge control diaphragm valve and the purge cut-off solenoid valve.

C. Fuel Tank Vapor Control System

When fuel vapor pressure in the fuel tank is higher than the set value of the two-way valve, the valve opens and regulates

the flow of fuel vapor to the canister.

(cont'd)
PURGE CUT-OFF SOLENOID VALVE OFF AFTER START-

ING ENGINE

COOLANT TEMPERATURE ABOVE 70°C (1 58°F)ProCarManuals.com

Emission Control System

Evaporative Emission Controls (cont'd)

FUEL

FILLER CAP

FUEL TANK

PURGE CUT-OFF

SOLENOID VALVE

ECU

TO No. 2

FUSE

BLK/YEL

GRN
TWO-WAY

VALVE

CANISTER

FRESH

AIR
PURGE CONTROL

DIAPHRAGM

VALVEProCarManuals.com

Troubleshooting Flowchart

Inspection of EvaporativeEmission Controls
PURGE CONTROL

DIAPHRAGM VALVE

VACUUM PUMP/GAUGE

A973X-041-XXXXX

Disconnect vacuum hose from the
purge control diaphragm valve (on
the charcoal canister) and connect
a vacuum gauge to the hose.
Start the engine and allow it to

idle.
NOTE: Engine coolant tempera-
ture must be below 70°C
(158°F).

Is there vacuum ? Disconnect the 6P connector.

BLK/YEL

GRN

Measure voltage between BLK/

YEL (+) terminal and GRN (-) ter-

minal.

Is there battery voltage ? Inspect vacuum hose
routing. If OK. replace purge
cut-off solenoid valve.
Measure voltage between BLK/
YEL (+) terminal and body
ground.
(To page 11-138)
(To page 11-138)

(cont'd)ProCarManuals.com

Emission Control System

Evaporative Emission Controls (cont'd)

(From page 11-137)
Warm up the engine to normal operating temperature (cooling
fan comes on). (From page 11-137)
Is there battery voltage ?

Inspect GRIM wire for an open

between ECU (A20) and the
connector. If wire is OK. substitute a
known-good ECU and recheck. If
symptom/incication goes away,
replace the orignal ECU.
Check for vacuum at #6 vacuum hose after starting the engine:
Is there manifold vacuum?
Disconnect the 6P connector.

Is there manifold vacuum?
Reconnect the hose. Inspect for a short to body
ground in GRN wire between ECU (A20) and the connector.
If wire is OK, substitute aknown-good ECU and recheck. If
symptom/indication goes away,
replace the original ECU.
Remove fuel filler cap.
(To page 11-139) Inspect vacuum hose
routing.
If OK, replace purge
cut-off solenoid valve. Repair open in BLK/
YEL wire between No. 2 fuse and the 6P con-
nector.ProCarManuals.com

(From page 11-138)
Connect a vacuum gauge to can-
ister purge air hose.
PURGE

HOSE

Start the engine and raise speed to

3,500 rpm.

Does vacuum appear on gauge

within 1 minute ?

See two-way valve test to com-

plete.

Evaporative emission control are

OK.
Connect a vacuum gauge to the

canister purge hose and raise the

engine speed to 3,500 rpm.

Does vacuum appear on the
gauge?
Replace the canister.

(cont'd)

Inspect the purge hose
and throttle body port

for pinch or blockage.
PURGE AIR

HOSE

VACUUM/PRESSURE
GAUGE, 0-4 in. Hg

07
JAZ-001000
AProCarManuals.com