1991 ACURA NSX catalytic converter

Three Way Catalytic Converter (TWC)

Description

The Three Way Catalytic Converter (TWC) is used to convert hydrocarbons (HC), carbon monoxide (CO), and oxides of

nitrogen
(NOx)
in the
exhaust
gas to
carbon
dioxide
(CO2),
dinitrogen
(Nz)
and
water
vapor.

SECONDARY HEATED OXYGEN SENSOR (SENSOR 2)

THREE WAY

CATALYST

HOUSINGProCarManuals.com

Exhaust System

Dual Exhaust System

A compact dual exhaust system is used to provide low back pressure.
Sound tuning has been optimized to give a sporty exhaust sound note suitable to this type of car. This is done by a col-
lection chamber in muffler.
MUFFLER

REAR
EXHAUST

PIPE

REAR EXHAUST

MANIFOLD

FRONT THREE WAY CATALYTIC

CONVERTER

REAR THREE WAY CATALYTIC

CONVERTER

FRONT
EXHAUST

PIPE

FRONT EXHAUST

MANIFOLD

Exhaust gas
from
rear bank

COLLECTION CHAMBER

Exhaust gas

from

front bank

FeaturesProCarManuals.com

Engine Removal/Installation

(cont'd)

40. Remove the heated oxygen sensor (HO2S) connectors.
41. Remove the self-locking nuts, then remove front exhaust pipe and the front three way catalyticconverter.
42. Remove the self-locking nuts, then separate the rear three way catalytic converter from rear ex-
haust pipe and the muffler.
CAUTION: Do not use an air wrench or hammer to
remove or install the exhaust system unless you

first remove the heated oxygen sensors.

NOTE: Use new gaskets and self-locking nuts
when reassembling.
NOTE: Perform steps 43 and 44 only if the
engine/transaxle assembly is to be removed from
the subframe.

SELF-LOCKING NUTS
10 x
1.25
mm

34 N .
m
(3.4
kg-m.
25 Ib-ft)
REAR THREE WAY

CATALYTIC
CONVERTER
GASKETS
Replace.

FRONT
EXHAUST PIPE
SELF-LOCKING NUT
10 x
1.25
mm

55 N .
m
(5.5
kg-m,
40 Ib-ft) DRIVESHAFTSET RING

Replace.

6 x 1.0 mm

10 N .
m (1.0 kg-m, 7 Ib-ft)
HALF SHAFT
HEAT COVER
43. Remove the half shaft heat cover.
44. Remove the driveshafts.

NOTE:
Coat all precision finished surfaces with clean
engine oil or grease.
Tie plastic bags over the driveshaft ends.ProCarManuals.com

Exhaust Pipe and Muffler

Illustrated Index
NOTE: Use new gaskets and self-locking nuts.

6 x 1.0 mm
10 N·m
(1.0 kg-m,
7 Ib-ft)
GASKET Replace.
REAR THREE WAY
CATALYTIC
CONVERTER

6 x 1.0 mm
10 N·m
(1.0 kg-m,
7 Ib-ft)
GASKET

Replace.
TO REAR EXHAUST MANIFOLD

GASKET
Replace.

EXHAUST PIPE
REAR
TO FRONT EXHAUST

MANIFOLD

GASKET
Replace.
SELF-LOCKING NUT
10 x
1.25
mm

55 N·m (5.5 kg-m, 40 Ib-ft)

Replace.

: CORROSION RESISTANT BOLT FRONT
EXHAUST PIPEMUFFLER
SELF-LOCKING NUT
10 x
1.5
mm

34 N·m (3.4 kg-m, 25 Ib-ft)

Replace.

6 x 1.0 mm
10 N·m (1.0 kg-m, 7 Ib-ft) FRONT THREE WAY CATALYTIC
CONVERTER
GASKET

Replace. SELF-LOCKING NUT

10 x
1.25
mm

34 N·m
(3.4 kg-m,
25 Ib-ft)
Replace.

ENGINE MOUNT

REAR BEAM
BRACKET
RUBBER MOUNT

GASKET

Replace.

SELF-LOCKING NUT
10 x
1.25
mm

34 N·m (3.4 kg-m, 25 Ib-ft)
Replace.

8 x
1.25
mm

22 N·m
(2.2 kg-m,
16 Ib-ft)ProCarManuals.com

System Description
Vacuum Connections (cont'd)
FRONT HEATED OXYGEN SENSOR (HO2S)
REAR HEATED OXYGEN SENSOR (HO2S)
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSORINTAKE AIR TEMPERATURE (IAT) SENSOR
FRONT KNOCK SENSOR (KS)
REAR KNOCK SENSOR (KS) IDLE AIR CONTROL (IAC) VALVE
FAST IDLE THERMO VALVE
AIR CLEANER (ACL) FUEL INJECTORFUEL PRESSURE REGULATOR
FUEL FILTER
FUEL PUMP (FP)
FUEL TANK
THROTTLE VALVE DASHPOT CONTROL DIAPHRAGM
THROTTLE VALVE DASHPOT CHECK VALVE INTAKE AIR BYPASS (IAB) CHECK VALVE
INTAKE AIR BYPASS (IAB) VACUUM TANK
INTAKE AIR BYPASS (IAB) CONTROL SOLENOID VALVE
INTAKE AIR BYPASS (IAB) CONTROL DIAPHRAGM
FRONT THREE WAY CATALYTIC CONVERTER (TWC)
REAR THREE WAY CATALYTIC CONVERTER (TWC)
POSITIVE CRANKCASE VENTILATION (PCV) VALVE
EXHAUST GAS RECIRCULATION (EGR) VALVE
EXHAUST GAS RECIRCULATION (EGR) VALVE LIFT SENSOR
EXHAUST GAS RECIRCULATION (EGR) VACUUM CONTROL VALVE
EXHAUST GAS RECIRCULATION (EGR) CONTROL SOLENOID VALVE
EVAPORATIVE EMISSION (EVAP) CONTROL CANISTER
EVAPORATIVE EMISSION (EVAP) PURGE CONTROL SOLENOID VALVE
EVAPORATIVE EMISSION (EVAP) PURGE CONTROL DIAPHRAGM VALVE
EVAPORATIVE EMISSION (EVAP) TWO WAY VALVEProCarManuals.com

System Description
Tailpipe Emission
The emission control system includes a three-way catalytic converter, exhaust gas recirculation (EGR) system,
crankcase ventilation system and evaporative control

system.

The emission control system is designed to meet federal and
state emission standards.
Inspection

Do not smoke during this procedure. Keep
any open flame away from your work area.
1. Starting the engine and warm it up to normal operating temperature by driving the car on theroad.
2. Connect a tachometer.
3. Check idle speed and adjust the idle speed, if necessary (page 11-84).
4. Warm up and calibrate the CO meter according to the meter manufacturer's instructions.
5. Check idle CO with the headlights, heater blower, rear window defogger, cooling fan, and air conditioner off.
CO meter should indicate 0.1 % maximum.ProCarManuals.com

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