1991 ACURA NSX Service Repair Manual

Fuel Injection Air (FIA) Control System

Description

The Fuel Injection Air (FIA) Control system enables fresh air to be drawn through the throttle body and fuel injector port.

IDLE ADJUSTING

SCREW
THROTTLE

BODY
FUEL INJECTOR
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Intake Air System

Intake Air Bypass (IAB) Control System

Description

Satisfactory power performance is achieved by closing and opening the intake air bypass (IAB) control valves. High torque

at low engine speed is achieved when the valves are closed, whereas high power at high engine speed is achieved when

the valves are opened.

INTAKE AIR BYPASS (IAB) CONTROL

SOLENOID VALVE ON

ENGINE SPEED IS ABOVE 4,800 rpm

OPEN: HIGH ENGINE SPEED

IAB CONTROL

SOLENOID

VALVE

To No. 5 BACK-UP LIGHTS

ALTERNATOR TURN SIGNALS

(15 A) FUSE

IAB

CONTROL

DIAPHRAGM

IAB

CONTROL

VALVE
CLOSED: LOW ENGINE SPEEDProCarManuals.com

Intake Ai r Bypas s (IAB ) Contro l Valv e Testin g
CAUTION : D o no t adjus t th e IA B contro l valv e full-clos e
screw . I t wa s prese t a t th e factory .
1 . Chec k th e IA B contro l valv e shaf t fo r bindin g o r
sticking .
2 . Chec k th e IA B contro l valv e fo r smoot h movement .
3. Chec k tha t o f th e IA B contro l valv e i s i n clos e
contac t wit h th e stoppe r whe n th e vacuu m hos e i s
disconnecte d fro m th e IA B contro l diaphragm .
STOPPER
4. Chec k tha t of the IA B contro l valv e i s i n clos e
contac t wit h th e full-clos e scre w whe n yo u appl y
50. 7 kP a (38 0 mmHg , 15. 0 in.Hg ) o f vacuu m to th e
IA B contro l diaphragm .
FULL-CLOS E
SCRE W
If an y faul t i s found , clea n th e linkag e an d shaft s
wit h carbureto r cleaner .
I f th e proble m stil l exist s afte r cleaning , disas -
sembl e th e intak e manifol d an d chec k th e IA B
valv e bod y assembl y (se e sectio n 9 ).
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Emission Contro l Syste m
System Descriptio n
The emissio n contro l syste m include s tw o Thre e Wa y
Catalyti c Converter s (TWCs) , Exhaus t Ga s Recirculatio n
(EGR ) system , Positiv e Crankcas e Ventilatio n (PCV ) sys -
te m an d Evaporativ e Emissio n (EVAP ) Contro l system .
Th e emissio n contro l syste m is designe d t o mee t federa l
an d stat e emissio n standards .
Tailpipe Emissio n
Inspectio n
Do no t smok e durin g thi s procedure . Kee p
an y ope n flam e awa y fro m you r wor k area .
1 . Star t th e engine . Hol d th e engin e a t 3,00 0 rp m wit h
no loa d (A/ T in position , M/ T in neutral ) unti l
the radiato r fa n come s on , the n le t i t idle .
2 . Connec t a tachometer .
3 . Chec k an d adjus t th e idl e speed , i f necessar y (se e
pag e 11-128 ).
4 . War m u p an d calibrat e th e C O mete r accordin g t o
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 condi -
tione r off .
NOTE : (Canada ) Pul l th e parkin g brak e leve r up .
Star t th e engine , the n chec k tha t th e headlight s ar e
off.
CO mete r shoul d indicat e 0.1 % maximum .
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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

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Exhaust Ga s Recirculatio n (EGR ) Syste m
The EG R syste m is designe d t o reduc e oxide s o f nitroge n emission s (NOx ) b y recirculatin g exhaus t ga s throug h th e EG R
valv e an d th e intak e manifol d int o th e combustio n chambers . I t i s compose d o f th e EG R valve , EG R vacuu m contro l valve ,
EGR contro l solenoi d valve , EC M an d variou s sensors .
The EC M contain s memorie s fo r idea l EG R valv e lift s fo r varyin g operatin g conditions . Th e EG R valv e lif t senso r detect s
th e amoun t o f EG R valv e lif t an d send s th e informatio n t o th e ECM . Th e EC M the n compare s it wit h th e idea l EG R valv e lif t
whic h i s determine d b y signal s sen t fro m th e othe r sensors . I f ther e is an y differenc e betwee n th e two , th e EC M varie s cur -
ren t t o th e EG R contro l solenoi d valv e to regulat e vacuu m applie d t o th e EG R valve .
EGRVALV ELIFTSENSO R
INTAKEMANIFOL D
To No . 5 BACK-U P
LIGHT S ALTERNATO R
TUR N SIGNAL S
(1 5 A ) FUS E
EGRVACUU MCONTRO LVALVE
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Emission Control System
Positive Crankcas e Ventilatio n (PCV ) Syste m
Descriptio n
Th e Positiv e Crankcas e Ventilatio n (PCV ) syste m is
designe d t o preven t blow-b y ga s fro m escapin g t o th e
atmosphere . Th e PCV valve contain s a spring-loade d
plunger . Whe n th e engin e starts , th e plunge r i n th e PC V
valv e i s lifte d i n proportio n t o intak e manifol d vacuu m
an d th e blow-b y ga s i s draw n directl y int o th e intak e
manifold .
PCV HOS EINTAK E MANIFOL D
PCV VALV E
Inspectio n
1. Chec k th e PC V hose s an d connection s fo r leak s an d
clogging .
BREATHE RPIPE
PCV HOS E PC
V VALV E
2. A t idle , mak e sur e ther e i s a clickin g soun d fro m th e
PC V valv e whe n th e hos e betwee n PC V valv e an d
intak e manifol d i n lightl y pinche d wit h you r finger s
o r pliers .
Gently pinc h her e
If ther e i s n o clickin g sound , chec k th e PC V valv e
gromme t fo r crack s o r damage . I f th e gromme t i s
OK , replac e th e PC V valv e an d recheck .
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Evaporative Emission (EVAP) Controls

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.

EVAP PURGE CONTROL SOLENOID VALVE OFF AFTER

STARTING ENGINE

ENGINE COOLANT TEMPERATURE ABOVE 153°F (67°C)

To No. 5 BACK-UP LIGHTS

ALTERNATOR TURN SIGNALS

(15 A) FUSE

FRESH

AIR
EVAP

PURGE CONTROL

DIAPHRAGM VALVE
EVAP PURGE

CONTROL

SOLENOID VALVE
EVAP PURGE

FLOW SWITCH
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

TWO WAY

VALVE
FUEL

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