1991 ACURA NSX Service Repair Manual

Emission Control System
System Troubleshooting Guide
NOTE
:
Across each row in the chart, the sub-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

143

145

151

152
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Emission Contro l Syste m
The emissio n contro l syste m include s a Thre e Wa y
Catalyti c Converter , Exhaus t Ga s Recirculatio n (EGR )
system , Positiv e Crankcas e Ventilatio n (PCV ) syste m
an d Evaporativ e Emissio n (EVAP ) contro l system .
Th e emissio n contro l syste m i s designe d t o mee t
federa l an d stat e emissio n standards .
Tailpipe Emissio n
1. Startin g th e engin e an d war m i t u p t o norma l
operatin g temperatur e (th e coolin g fa n come s on )
b y drivin g th e ca r o n th e road .
2 . Connec t a tachometer .
3 . Chec k idl e spee d an d adjus t th e idl e speed , i f
necessar y (se e pag e 11-102 ).
4 . War m up an d calibrat e th e C O mete r accordin g to th e
mete r manufacturer' s instructions .
5 . Chec k idl e C O wit h th e headlights , heate r blower , rea r
windo w defogger , coolin g fan , an d ai r conditione r off .
C O mete r shoul d indicat e 0. 1 % maximum .
System Descriptio n
Do no t smok e durin g thi s procedure . Kee pany ope n flam e awa y fro m you r wor k area .
Inspectio n
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Three Wa y Catalyti c Converte r (TWC)
Descriptio n
The Thre e Wa y Catalyti c Converte r (TWC ) i s use d t o conver t hydrocarbon s (HC), carbon monoxide (CO), and oxides of
nitroge n (NOx ) i n th e exhaus t gas , t o carbo n dioxid e (CO
2), dinitroge n (N2) an d wate r vapor .
HOUSIN G
THREE WA YCATALYS TFRONT O FVEHICL E
(cont'd)
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Emission Contro l Syste m
Three Wa y Catalyti c Converte r (cont'd )
Inspectio n
If excessiv e exhaus t syste m back-pressur e i s suspected , remov e th e thre e wa y catalyti c converte r fro m th e ca r an d
mak e a visua l chec k fo r plugging , meltin g o r crackin g o f th e catalyst . Replac e th e thre e wa y catalyti c converte r i f an y o f
the visibl e are a i s damage d o r plugged .
34 N· m (3. 4 kg-m ,25 Ib-ft )
GASKE TReplace .
FRONT O FVEHICL E
GASKE TReplace .
HEAT SHIEL D
HEA T SHIEL D
10 N.m (1. 0 kg-m , 7 Ib-ft )
3
4 N
.m (3. 4 kg-m , 2 5 Ib-ft )
REAR THRE E WA YCATALYTI CCONVERTE RRemoval/Installation , se e sectio n 9
Inspec t housin g fo r crack s o r
othe r damage .
Inspec t elemen t fo r cloggin g b y
lookin g throug h th e inside .
34 N· m (3. 4 kg-m ,25 Ib-ft )
HEA
T SHIEL D FRON
T THRE E WA Y
CATALYTI CCONVERTE RRemoval/Installation , se e sectio n 9
Inspec t housin g fo r crack s o r
othe r damage .
Inspec t elemen t fo r cloggin g b y
lookin g throug h th e inside .
10 N· m (1. 0 kg-m , 7 Ib-ft )
HEA
T SHIEL D
34 N· m (3. 4 kg-m , 2 5 Ib-ft )
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Positive Crankcase Ventilation (PCV) System

Description

The Positive Crankcase Ventilation (PCV) system is

designed to prevent blow-by gas from escaping to the

atmosphere. 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

BREATHER PIPE

FRONT OF

VEHICLE

BLOW-BY VAPOR

FRESH AIR

PCV VALVE

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.
Gently pinch here
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.
BREATHER

PIPE
PCV VALVE PCV HOSE
Inspection

1. Check the PCV hoses and connections for leaks

and clogging.ProCarManuals.com

Emission Control System

Description

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

system consists of the following components:

A. Evaporative Emission (EVAP) Control Canister

An EVAP control canister is used for the temporary storage of fuel vapor until the fuel vapor can be purged from the

EVAP control canister into the engine and burned.

B. Vapor Purge Control System

EVAP control canister purging is accomplished by drawing fresh air through the EVAP control canister and into a port

on the throttle body. The purging vacuum is controlled by the EVAP purge control diaphragm valve and the EVAP

control solenoid valve.

C. Fuel Tank Vapor Control System

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

and regulates the flow of fuel vapor to the EVAP control canister.
EVAP PURGE CONTROL SOLENOID VALVE OFF AFTER

STARTING ENGINE

ENGINE COOLANT TEMPERATURE ABOVE
158°F
(70°C)
Evaporative Emission (EVAP) ControlsProCarManuals.com

FUEL

FILL CAP

FUEL TANK

EVAP

CONTROL

CANISTER
FRESH

AIR
EVAP

PURGE CONTROL

DIAPHRAGM

VALVE

(cont'd)
BLK
ECM

TO No. 2

(15 A) FUSE

GRN
EVAP PURGE

CONTROL

SOLENOID VALVE

EVAP

TWO WAY

VALVEProCarManuals.com

Emission Contro l Syste m
Troubleshootin g Flowchar t
Evaporativ e Emissio n (EVAP ) Control s (cont'd )
(To pag e 11-155 ) (To pag e 11-155 )
GRN
BLK /YEL
VACUU M PUMP/GAUG EA973X–041–XXXXX
EVAPCONTRO LCANISTE R
EVAPPURG E CONTRO L
DIAPHRAG M VALV EInspectio n o f Evaporativ eEmission Control s
Disconnec t vacuu m hos e fro m
th e EVA P purg e contro l dia -
phrag m valv e (o n th e EVA P con -
trol canister ) an d connec t a vac -uum gaug e t o th e hose .
Star t th e engin e an d allo w i t t o
idle .NOTE : Engin e coolan t tempera -ture mus t b e belo w 158° F(70°C).
Is ther e vacuu m ?
Disconnec t th e 6 P connecto rfrom th e contro l box .
Measur e voltag e betwee n BLK /YEL (+ ) termina l an d GR N ( - ) ter-minal .
Is ther e batter y voltag e ?
Measur e voltag e betwee n BLK /
YE L ( + ) termina l an d bod y
ground . Inspec
t vacuu m hos e
routing .
I f OK . replac e th e
EVA P purg e contro l
solenoi d valve .
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