1991 ACURA NSX light

PGM-FI Syste m
System Descriptio n
3. Fue l Cut-of f Contro l
• Durin g deceleratio n wit h th e throttl e valv e closed , curren t t o th e fue l injector s i s cu t of f t o improv e fue l econom y a t
speed s ove r 1,50 0 rpm .
• Fue l cut-of f actio n als o take s plac e whe n engin e spee d exceeds , 8,30 0 rpm , regardles s o f th e positio n o f th e throttl e
valve , t o protec t th e engin e fro m over-revving .
4 . A/ C Compresso r Clutc h Rela y
Whe n th e EC M receive s a deman d fo r coolin g fro m th e ai r conditionin g system , i t delay s th e compresso r fro m bein g
energized , an d enriche s th e mixtur e to assur e smoot h translatio n to th e A/ C mode .
5 . Evaporativ e Emissio n (EVAP ) Purg e Contro l Solenoi d Valv e
Whe n th e engin e coolan t temperatur e is belo w 153° F (67°C) , th e EC M control s th e EVA P purg e contro l solenoi d valv e
whic h cut s vacuu m to th e EVA P purg e contro l caniste r diaphragm .
6 . Intak e Ai r Bypas s (IAB ) Contro l Solenoi d Valv e
Whe n th e engin e spee d is belo w 4,80 0 rpm , th e IA B contro l solenoi d valv e is activate d b y a signa l fro m th e ECM . Intak e
ai r the n flow s throug h th e smalle r chamber , an d hig h torqu e is delivered . T o increas e ai r flo w a t engin e speed s highe r
tha n 4,80 0 rpm , th e solenoi d valv e is deactivate d b y th e ECM , an d th e intak e ai r flow s throug h th e large r chamber .
7 . Exhaus t Ga s Recirculatio n (EGR ) Contro l Solenoi d Valv e
Whe n th e EG R is require d fo r contro l o f oxide s o f nitroge n (NOx ) emissions , th e EC M supplie s groun d t o th e EG R
contro l solenoi d valv e whic h supplie s regulate d vacuu m to th e EG R valve .
EC M Fail-safe/Back-u p Function s
1 . Fail-Saf e Functio n
Whe n a n abnormalit y occur s i n a signa l fro m a sensor , th e EC M ignore s tha t signa l an d assume s a pre-programme d
valv e fo r tha t senso r tha t allow s th e engin e t o continu e t o run .
2 . Back-u p Functio n
Whe n a n abnormalit y occur s i n th e EC M itself , th e fue l injector s ar e controlle d b y a back-u p circui t independen t o f th e
syste m in orde r t o permi t minima l driving .
3 . Self-diagnosi s Functio n [Malfunctio n Indicato r Lam p (MIL) ]
Whe n a n abnormalit y occur s i n a signa l fro m a sensor , th e EC M light s th e MI L an d store s th e diagnosti c troubl e cod e
i n erasabl e memory . Whe n th e ignitio n i s initiall y turne d on , th e EC M supplie s groun d fo r th e MI L fo r tw o second s t o
chec k th e MI L bul b condition .
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Engine Control Module (ECM)

NOTE: If this symptom is intermittent, check for a loose No. 5 BACK-UP LIGHTS, ALTERNATOR,

TURN SIGNALS (15 A) fuse in the under-dash fuse/relay box, a poor connection at ECM terminal

A7, or an intermittent open in the BLU wire between the ECM (A7) and the gauge assembly.

Is the low oil pressure light on?

Try to start the engine.

Does the engine start?

Check for an open in the wire or

bulb:

1. Turn the ignition switch OFF.

2. Connect the ECM connector ter-

minal A7 to body ground with a

jumper wire.

3. Turn the ignition switch ON (II).

Is the MIL on?

Substitute a known-good ECM,

and recheck. If symptom/indica-

tion goes away, replace the origi-

nal
ECM.
— Repair short in the wire

between No. 5 BACK-UP

LIGHTS, ALTERNATOR, TURN

SIGNALS (15 A) fuse and

gauge assembly.

— Replace No. 5 BACK-UP

LIGHTS, ALTERNATOR, TURN

SIGNALS (15 A) fuse.

ECM CONNECTOR A (26P)

Check for an open in the wires

(PG line):

1. Turn the ignition switch ON (II).

2. Measure voltage between

body ground and ECM connec-

tor terminals A12 and A25 indi-

vidually.
WIRE SIDE OF FEMALE TERMINALS

Is there less than 1.0 V?
Repair open in the wire(s)

between ECM and G101 (located

at intake manifold) that had

more than 1.0V.

— Repair open in the wires

between ECM (A7) and gauge

assembly.

— Replace the MIL bulb.
WIRE SIDE OF FEMALE TERMINALS
ECM CONNECTOR A (26P)
Substitute a known-good ECM

and recheck. If symptom/indica-

tion goes away, replace the origi-

nal
ECM.
Turn the ignition switch ON (II).
The Malfunction Indicator Lamp

(MIL) never comes on (even for

two seconds) after ignition is

turned ON (II).ProCarManuals.com

Alternator (ALT ) F R Signa l
This signal s th e EC M whe n th e Alternato r (ALT ) i s charging .
Inspection o f AL T F R Signal .
ECM CONNECTOR S
WIR E SID E O F FEMAL E TERMINAL S
Chec k fo r a shor t i n th e wire :
1. Tur n th e ignitio n switc h OFF .2. Disconnec t th e negativ e bat -
ter y cabl e fro m th e battery .
3 . Disconnec t th e EC M connec -
tor D (22P ) fro m th e ECM .4. Chec k fo r continuit y betwee n
EC M connecto r termina l D 5
an d bod y ground .
I
s ther e approx . 5 V ?
Chec
k fo r a shor t i n th e circuit :
1 . Disconnec t th e GR N 4 P con -
necto r fro m th e ALT .
2. Tur n th e ignitio n switc h O N (II) .3. Measur e voltag e betwee n EC M
connecto r terminal s D 5 an d
A26 .
Is ther e continuity ? Repai
r shor t i n th e wir e betwee nthe EC M (D5 ) and th e ALT .
Substitut e a known-goo d EC M
an d recheck . I f prescribe d voltag e
i s no w available , replac e th e origi -
nal ECM .Chec k th e operatio n o f th e ALT :1. Tur n th e ignitio n switc h OFF .2. Reconnec t th e AL T GR N 4 P
connecto r t o th e ALT .
3 . Star t th e engine . Hol d th e
engin e a t 3,00 0 rp m wit h n oloa d (A/ T in position ,M/T in neutral ) unti l th e radiato r
fa n come s on , the n le t i t idle .
4 . Measur e voltag e betwee n EC M
connecto r terminal s D 5 an d
A26.
Doe s th e voltag e decreas e whe nhead light s an d rea r defogge r ar eturne d on ? AL
T F R signa l i s OK .
(T o pag e 11-120 )
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Idle Contro l Syste m
Brake Switc h Signa l
This signal s th e EC M whe n th e brak e peda l i s depressed .
Are th e brak e light s o n withou tdepressin g th e brak e pedal ?Inspec t th e brak e switc h (se e
sectio n 19 ).
Depres s th e brak e pedal .
D o th e brak e light s com e on ?
Is th e fus e OK ?
Chec k fo r a n ope n in th e wire :
1 . Depres s th e brak e pedal .
2 . Measur e voltag e betwee n
EC M connecto r terminal s F1 6
an d A2 6 wit h th e brak e peda l
depressed . —
Repai r shor t i n th e wir e
betwee n th e brak e switc h
an d th e BRAK E LIGH T S W
HOR N (2 0 A ) fuse .
— Replac e th e BRAK E LIGH T
S W HOR N (2 0 A ) fuse .
WIR E SID E O F FEMAL E TERMINAL S
I s ther e batter y voltage ? Repai
r ope n i n th e wir e betwee n
th e EC M (F16 ) an d th e brak e
switch .
Inspectio
n o f Brak e Switc h Signal .
Inspect th e BRAK E LIGH T S W
HORN (20 A ) fus e i n th e under -
hood fuse/rela y box .
Repai r ope n i n th e wir e
betwee n th e brak e switc h
an d th e BRAK E LIGH T S W
HOR N (2 0 A ) fuse .
Inspec t th e brak e switc h (se e
sectio n 19 ).
ECM CONNECTOR S
Brak e switc h signa l i s OK .
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Idle Contro l Syste m
Idle Spee d Settin g
Inspection/Adjustmen t
NOTE: Befor e settin g th e idl e speed , chec k th e followin g
items :
— Th e Chec k Engin e ligh t ha s no t bee n reporte d on .
— Ignitio n timin g
— Spar k plug s
— Ai r cleane r
— PC V syste m
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
th e radiato r fa n come s on , the n tur n th e ignitio n
switc h OFF .
2 . Connec t th e SC S servic e connecto r t o servic e chec k
connector .
3. Connec t a OBDI I sca n too l (se e pag e 11-38 ) o r
tachometer .
• Connec t a tachomete r t o loo p o f ignite r uni t sec -
ondary , or.. .
TACHOMETE R
Remove th e rubbe r ca p fro m th e tachomete r
connector an d connec t a tachometer .
TACHOMETE R
RUBBERCAP
TACHOMETE RCONNECTOR
4. Restar t th e engine .
5 . Chec k idlin g i n no-loa d condition s i n whic h th e
headlights , blowe r fan , rea r defogger , coolin g fan ,
an d ai r conditione r ar e no t operating .
NOTE : D o no t depres s th e accelerato r peda l i n thi s
step .
Idl e spee d shoul d be :
Adjus t th e idl e speed , i f necessary , b y turnin g th e
idl e adjustin g screw .
NOTE : Afte r adjustin g th e idl e spee d i n thi s step ,
chec k th e ignitio n timin g (se e sectio n 23 ).
I f i t i s ou t o f spec , g o bac k t o ste p 4 .
IDL E ADJUSTIN GSCREW
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Fuel Suppl y Syste m
Fuel Pum p Rela y
(From pag e 11-139 )
FUEL PUM P RELA Y 4 P CONNECTO R
Chec k fo r ope n i n th e fue l pum p
relay:1. Tur n th e ignitio n switc h OFF .2. Disconnec t th e EC M connec -tor F (26P ) fro m th e ECM .3. Disconnec t th e 4 P connecto r
fro m th e fue l pum p relay .
4 . Connec t fue l pum p rela y con -
necto r terminal s No . 2 to No . 4 .
5. Tur n th e ignitio n switc h O N (II) .6. Measur e voltag e betwee n
EC M connecto r termina l F 4
an d bod y ground . CAUTION
: * th e "A " connecto r mus t b e
disconnecte d fo r thi s tes t o r th e EC M
will b e damaged .
WIRE SID E O F FEMAL E TERMINAL S
EC M CONNECTO R F (26P )
WIR E SID E O F FEMAL E TERMINAL S
I s ther e batter y voltage ?
Replace th e fue l pum p relay .
Chec k fo r a n ope n in th e wire :
1 . Remov e th e jumpe r wire .
2 . Measur e voltag e betwee n th e
fue l pum p rela y connecto r ter -
mina l No . 2 an d bod y ground .
I s ther e batter y voltage ? Repai
r ope n i n wir e betwee n th e
fue l pum p rela y an d th e No . 5
BACK-U P LIGHT S ALTERNATO R
TUR N SIGNAL S (1 5 A ) fus e in th e
under-das h fus e box) .
Repai r ope n o r shor t i n wir e
betwee n EC M (F4 ) an d th e fue l
pum p relay .
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Intake Air System

System Description

The system supplies air for all engine needs. It consists of the intake air pipe, Air Cleaner (ACL), intake air duct, throttle

body, and intake manifold. A resonator in the intake air duct provides additional silencing as air is drawn into the system.

IAB CONTROL

SOLENOID VALVE

To No. 5 BACK-UP LIGHTS

ALTERNATOR TURN SIGNALS

(15 A) FUSE

IAB

CONTROL

DIAPHRAGM

IAB

CONTROL

VALVE
THROTTLE

VALVE
INTAKE

AIR DUCT
ACL
RESONATOR
VARIOUS

SENSORS

INTAKE

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Throttle Bod y
Descriptio n
The throttl e bod y is o f th e single-barre l side-draf t type .
Th e lowe r portio n o f th e throttl e valv e i s heate d b y
engin e coolan t whic h is fe d fro m th e cylinde r head . Th e
idl e adjustin g screw , whic h increases/decrease s bypas s
air , an d th e evaporativ e emissio n (EVAP ) contro l caniste r
por t ar e locate d o n th e to p o f th e throttl e body .
IDLE ADJUSTIN GSCREW
THROTTL E VALV ECONTRO L MOTO R
TPSENSO RTHROTTL EVALVE
Inspectio n
CAUTION : D o no t adjus t th e throttl e sto p screw . I t i s
prese t a t th e factory .
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
th e radiato r fa n come s on , the n le t i t idle .
2. Disconnec t th e vacuu m hos e (t o th e EVA P contro l
canister ) fro m th e to p o f th e throttl e body ; connec t
a vacuu m gaug e to th e throttl e body .
VACUU M PUMP/GAUG EA973X-04 1-XXXX X
3. Allo w th e engin e t o idl e an d chec k tha t th e gaug e
indicate s n o vacuum .
• I f ther e i s vacuum , chec k th e throttl e cabl e (se e
page 11-150 ).
4 . Chec k tha t vacuu m is indicate d o n th e gaug e whe n
th e throttl e is opene d slightl y fro m idle .
• I f th e gaug e indicate s n o vacuum , chec k th e
throttl e bod y port . I f th e throttl e bod y por t i s
clogged , clea n it wit h carbureto r cleaner .
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