1991 ACURA NSX Service Repair Manual

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Diagnosti c Troubl e Cod e (DTC ) Char t
Troubleshootin g
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indicator ligh t an d th e Malfunctio n Indicato r Lam p (MIL ) ma y com e o n simultaneously .The
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Troubleshooting
How to Rea d Flowchart s
A flowchar t i s designe d to b e use d fro m star t t o fina l repair . It' s lik e a ma p showin g yo u th e shortes t distance . Bu t beware :
i f yo u g o of f th e "map " anywher e bu t a "stop " symbol , yo u ca n easil y ge t lost .
Describe s th e condition s o r situatio n to star t a troubleshootin g flowchart .
Ask s yo u to d o something ; perfor m a test , se t u p a conditio n etc .
Ask s yo u abou t th e resul t o f a n action , the n send s yo u in th e appropriat e troubleshootin g direction .
Th e en d o f a serie s o f action s an d decisions , describe s a fina l repai r actio n an d sometime s direct s yo u to
a n earlie r par t o f th e flowchar t t o confir m you r repair .
NOTE:
The ter m "Intermitten t Failure " i s use d in thes e charts . I t simpl y mean s a syste m ma y hav e ha d a failure , bu t i t check s
ou t O K a t thi s time . I f th e Malfunctio n Indicato r Lam p (MIL ) o n th e das h doe s no t com e on , chec k fo r poo r connection s
o r loos e wire s a t al l connector s relate d to th e circui t tha t yo u ar e troubleshootin g (se e illustratio n below) .
Mos t o f th e troubleshootin g flowchart s hav e yo u rese t th e Engin e Contro l Modul e (ECM ) an d tr y t o duplicat e th e
Diagnosti c Troubl e Cod e (DTC) . I f th e proble m is intermitten t an d yo u can' t duplicat e th e code , d o no t continu e throug h
th e flowchart . T o d o s o wil l onl y resul t i n confusio n and , possibly , a needlessl y replace d ECM .
"Open " an d "Short " ar e commo n electrica l terms . A n ope n i s a brea k i n a wir e o r a t a connection . A shor t i s a n acci -
denta l connectio n o f a wir e t o groun d o r t o anothe r wire . I n simpl e electronics , thi s usuall y mean s somethin g won' t
wor k a t all . I n comple x electronic s (lik e ECM's) , thi s ca n sometime s mea n somethin g works , bu t no t th e wa y it' s sup -
pose d to .
TIGH T
LOOS E
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PGM-FI System

System Description

PGM-FI System

The PGM-FI system on this model is a sequential multiport fuel injection system.

Fuel Injector Timing and Duration

The ECM contains memories for the basic discharge durations at various engine speeds and manifold pressures. The

basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors

to obtain the final discharge duration.

Throttle Valve Control

The ECM controls the throttle valve control motor based on accelerator pedal position, TCS control unit and various sig-

nals. The ECM also controls the idle control function, cruise control function, and other functions with the throttle valve

control.

Ignition Timing Control

• The ECM contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing

is also adjusted for engine coolant temperature.

• A knock control system is also used. When detonation is detected by the knock sensor (KS), the ignition timing is

retarded.

Other Control Functions

1. Starting Control

When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration.

2. Fuel Pump Control

• When the ignition switch is initially turned on, the ECM supplies ground to the PGM-FI main relay that supplies

current to the fuel pump for two seconds to pressurize the fuel system.

• When the engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.

• When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay which cuts

current to the fuel pump.

• Excellent engine performance is achieved through the use of VTEC (Variable Valve Timing and Valve Lift Electronic

Control System), intake air bypass control and discharge volume control of the fuel pump.ProCarManuals.com

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

PGM-FI Syste m
Engine Contro l Modul e (ECM )
The Malfunctio n Indicato r Lam p
(MIL ) stay s o n o r come s o n afte r
tw o seconds .
Check th e Diagnosti c Troubl eCode (DTC) :
1 . Connec t a sca n too l o r Hond a
PG M Tester .
2 . Tur n th e ignitio n switc h O N (II) .
3 . Rea d th e DT C wit h th e sca n
too l o r Hond a PG M Tester .
NOTE:• Whe n ther e is n o Diagnosti c Troubl e Cod e (DTC ) stored , th e MI L wil l sta y o n i f th e SC S servic e
connecto r i s connecte d an d th e ignitio n switc h i s on .
• I f thi s sympto m is intermittent , chec k for :
— A loos e ACG(S ) (20 A ) fus e in th e engin e compartment fuse/rela y box— A loos e No . 2 FUE L PUM P SRS 2 (1 5 A ) fus e in th e under-das h fus e bo x
— A n intermitten t shor t i n th e wir e betwee n th e EC M (C5 ) an d th e servic e chec k connecto r
— A n intermitten t ope n i n th e wire s betwee n th e EC M (A26 , B14 ) an d th e servic e chec k con -
necto r
— A n intermitten t shor t i n th e wir e betwee n th e EC M (A7 ) an d th e gaug e assembl y— A n intermitten t shor t i n th e wir e betwee n th e EC M (F1 ) an d th e MA P sensor , accelerato r posi -
tio n senso r
— A n intermitten t shor t i n th e wir e betwee n th e EC M (D10 ) an d th e T P sensor , EG R valv e lif t
senso r— A n intermitten t shor t i n th e wir e betwee n th e EC M (F14 ) an d accelerato r positio n senso r
• Se e th e OBD-I I sca n too l o r Hond a PG M Teste r user' s manual s fo r specifi c operatin g instruc -
tions .
Ar e an y DTC(s ) indicated ? G
o to troubleshootin g procedures .
(se e pag e 11-38 )
Chec k th e DT C b y MI L indication :
1 . Tur n th e ignitio n switc h OFF .
2 . Connec t th e SC S servic e con -
necto r t o th e servic e chec k
connector .
3 . Tur n th e ignitio n switc h O N (II) .
Doe s th e MI L indicat e an y DTC ? Repai
r ope n o r shor t i n wir e
betwee n th e EC M (D4 ) an d
Dat a Lin k Connector .
G o t o troubleshootin g proce -
dures . (se e pag e 11-38 )
Tr y t o star t th e engine .
Doe s th e engin e start ?
Chec k fo r a shor t i n th e wire s
(SC S line) :
1. Sto p th e engin e an d tur n th eignitio n switc h O N (II) .2. Measur e voltag e betwee n th e
EC M connecto r termina l C 5
an d bod y ground . (T
o pag e 11-63 )
I s ther e approx . 5 V ?
(T o pag e 11-63 ) Repai
r shor t t o bod y groun d i n
th e wir e betwee n EC M (C5 ) an d
servic e chec k connector .
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(From pag e 11-62 )
Chec k fo r a shor t i n th e wire s
(MI L line) :
1. Tur n th e ignitio n switc h OFF .2. Disconnec t th e EC M connec -tor A (26P) .3. Tur n th e ignitio n switc h O N (II) .
Is th e MI L ON ?Repai r shor t t o bod y groun d i n
th e wir e betwee n th e EC M (A7 )
and MIL .
Substitut e a known-goo d EC M
an d recheck . I f symptom/indica -
tio n goe s away , replac e th e origi -
nal ECM .
(From pag e 11-62 )
Inspec t ACG(S ) (2 0 A ) fus e i n th e
engin e compartmen t fuse/rela y
box.
Is th e fus e OK ? Repai
r shor t i n th e wir e
betwee n ACG(S ) (2 0 A ) fus e
an d PGM-F I mai n relay .
Replac e ACG(S ) (2 0 A ) fuse .
Inspec t I G COI L (3 0 A ) fus e i n th e
engin e compartmen t fuse/rela y
box.
Is th e fus e OK ? Repai
r shor t i n th e wir e
betwee n I G COI L (3 0 A ) fus e
an d PGM-F I mai n relay .
Replac e IG COI L (3 0 A ) fuse .
Chec k fo r a shor t i n a sensor :
1. Tur n th e ignitio n switc h O N (II) .2. Disconnec t th e 3 P connecto r
o f eac h senso r on e a t time :
• MA P senso r
• T P senso r
• EG R valv e lif t senso r
Doe s th e MI L remai n ON ? Replac
e th e senso r tha t cause d
the ligh t t o g o out .
(To pag e 11-64 )
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