1991 LEXUS SC400 EFI

Troubleshooting
If the HC/CO concentration does not comply with regulations,
perform troubleshooting in the order given below.
(a) Check oxygen sensor operation.(See page FI±113)
(b) See the table below for possible cause, and then inspect
and correct the applicable causes if necessary.
 

HC 

CO 

Symptoms\
 

\
Cause
 High Normal Rough idle\
 \
1. Faulty ignitions:
   \
 \

Incorrect timing
   \
 \

Fouled, shorted or improperly gapped plugs
   \
 \

Open or crossed high±tension cords
Ckddiib\

Cracked distributor cap
Ill   \
 \
2. Incorrect valve clearance
3 L k EGR l   \
 \
3. Leaky EGR valve
4L k i k d h l   \
 \
4. Leaky intake and exhaust valves
L k li d   \
 \
5. Leaky cylinders
 High Low Rough idle\
 \
1. Vacuum leaks:
   (Fluctuating HC reading)\
 \

PCV hoses
   \
 \

EGR valve
   \
 \

Intake manifold
Ai i k h b   \
 \

Air intake chamber
Th l b d   \
 \

Throttle body
ISC l\

ISC valve
Bkb li   \
 \

Brake booster line
2L i i ifi   \
 \
2. Lean mixture causing misfire
 High High Rough idle\
 \
1. Clogged air filter g g g
(Black smoke from exhaust)\
 \
gg
2. Faulty EFI systems:   ()\
 \
yy

Faulty pressure regulator
   \
 \

yg

Clogged fuel return line
   \
 \

gg

Defective water temp. sensor
   \
 \

Defective air temp. sensor
   \
 \

Faulty ECU
   \
 \

y

Faulty injectors
\

yj

Faulty cold start injector   \
 \
yj

Faulty throttle position sensor   \
 \

Faulty air flow meter
±
ENGINE MECHANICAL Idle and/or 2,500 rpm HC/CO
Concentration Check MethodEM±29
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Injectors
ON±VEHICLE INSPECTION
INSPECT INJECTOR RESISTANCE(a) Remove the engine wire covers and throttle body.(See steps 1 to 8 and 13 on pages FI±27 to 30)
(b) Disconnect the injector connectors.
(c) Using an ohmmeter, measure the resistance between the terminals.
Resistance: 13.4±14.2

If the resistance is not as specified, replace the injector.
(d) Reconnect the injector connectors.
(e) Reinstall the throttle body and engine wire covers.
(See steps 5 and 10 to 18 on pages FI±38 to 41)
FI±48
± Fuel System (Injectors)EFI SYSTEM
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COMPONENTS FOR REMOVAL AND INSTALLATION
FI±49EFI SYSTEM ± Fuel System (Injectors)
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REMOVAL OF INJECTORS
(See Components on page FI±49)
1. REMOVE AIR INTAKE CHAMBER (See steps 1 to 16 on pages FI±27 to 32)
2. DISCONNECT FUEL INLET HOSE FROM LH DELIVERY PIPE
Remove the pulsation damper and two gaskets, and discon-
nect the inlet hose.
3. DISCONNECT FUEL RETURN HOSE FROM FUEL RETURN PIPE
4. DISCONNECT EGR PIPE FROM RH CYLINDER HEAD Remove the bolt holding the EGR pipe to the cylinder head,
and disconnect the EGR pipe.
5. DISCONNECT ENGINE WIRE FROM INTAKE MANIFOLD Remove the two bolts, and disconnect the engine wire.
6. DISCONNECT ENGINE WIRE FROM DELIVERY PIPES AND REAR WATER BY±PASS JOINT
(a) Remove the four bolts holding the engine wire to thedelivery pipes, and disconnect the engine wire from the
delivery pipes.
(b) Remove the two bolts holding the engine wire to the rear
water by±pass joint, and disconnect the engine wire
from the rear water by±pass joint.
(c) Remove the two bolts holding the engine wire to the rear
side of the RH cylinder head, and disconnect the engine
wire from the RH cylinder head.
FI±50
EFI SYSTEM
± Fuel System (Injectors)
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(d) Disconnect the two engine wire connectors from theconnector bracket on the front side of the LH delivery
pipe.
(e) Disconnect the eight injector connector.
7. REMOVE FUEL RETURN PIPE (a) Remove the bolt holding the return pipe to the LHcylinder head.
(b) Remove the union bolt and two gaskets and return pipe.
8. REMOVE DELIVERY PIPES AND INJECTORS (a) Remove the four nuts holding the delivery pipe to theintake manifold.
(b) Remove the connector bracket, the two delivery pipes and eight injector assembly, four spacers and eight
insulators.
NOTICE: Be careful not to drop the injectors, when re-
moving the delivery pipe.
(c) Pull out the eight injectors from the delivery pipes.
(d) Remove the O±ring and grommet from each injector. FI±51
EFI SYSTEM
± Fuel System (Injectors)
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INSPECTION OF INJECTORS
1. INSPECT INJECTOR INJECTIONCAUTION: Keep injector clear of sparks during the test.
(a) Disconnect the fuel inlet hose from the fuel tube.
(b) Connect SST (hose) to the fuel inlet tube with SST(union). Tighten the flare nut on the fuel tube.
SST 09268±41045 (90405±52010)
Torque: 30 N Vm (310 kgf Vcm, 22 ft Vlbf)
HINT: Use SST. (See page FI±15)
SST 09631±22020
(c) Loosen the lock nut, and remove the pressure regulator from the RH delivery pipe. Remove the O±ring from the
pressure regulator.
(d) Install a new O±ring to the fuel inlet of the pressure regulator.
(e) Connect SST (hose) to the pressure regulator with SST (union). Tighten the lock nut on the pressure regulator.
SST 09268±41045 (09268±52010)
Torque: 29 N Vm (300 kgf Vcm, 22 ft Vlbf)
(f) Connect the fuel return hose to the fuel outlet of the
pressure regulator with SST (union), two new gaskets
and union bolt.
SST 09268±41045 (09268±41070)
FI±52EFI SYSTEM ± Fuel System (Injectors)
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(g) Install the grommet and a new O±ring to the injector.
(h) Connect SST (hose) to the injector with SST (union),and hold the injector and union with SST (clamp).
SST 09268±41045
(i) Put the injector into the graduated cylinder.
HINT: Install a suitable vinyl hose onto the injector to prevent
gasoline from splashing out.
(j) Using SST, connect terminals +B and FP of the check (ºDIAGNOSISº) connector.
SST 09843±18020
(k) Reconnect the cable to negative (±) terminal of battery.
(l) Turn the ignition switch ON.
NOTICE: Do not start the engine.
(m) Connect SST (wire) to the injector and battery for 15 seconds, and measure the injection volume with a
graduated cylinder. Test each injector two or three
times.
SST 09842±30070
Volume: 55±70 cc (3.4±4.3 cu in.) per 15 sec.
Difference between each injector:
10 cc (0.6 cu in.) or less
If the injection volume is not as specified, replace the injector.
2. INSPECT LEAKAGE (a) In the condition above, disconnect the test probes ofSST (wire) from the battery and check the fuel leakage
from the injector.
SST 09842±30070
Fuel drop: One drop or less per minute
(b) Disconnect the battery negative (±) cable.
(c) Remove SST.
SST 09268±41045 and 09843±18020
(d) Reconnect the fuel inlet hose to the fuel tube.
SST 09631±22020
Torque: 30 N Vm (310 kgf Vcm, 22 ft Vlbf)
HINT: Use a torque wrench with a fulerum length of 30 cm
(11.81 in.). FI±53
EFI SYSTEM
± Fuel System (Injectors)
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(e) Reinstall the fuel pressure regulator to the RH deliverypipe.
w Fully loosen the lock nut on the pressure regulator.
w Apply a light coat of gasoline to a new O±ring, and
install it to the pressure regulator.
w Completely insert the pressure regulator into the
delivery pipe by hand.
w Turn the pressure regulator counterclockwise until
the vacuum sensing port faces in the direction
indicated in the illustration.
INSTALLATION OF INJECTORS
(See Components on page FI±49)
1. INSTALL INJECTORS AND DELIVERY PIPE (a) Install the grommet to each injector.
(b) Apply a light coat of gasoline to a new O±ring and install
it to each injector.
(c) W h i l e t u r n i n g t h e i n j e c t o r c l o c k w i s e a n d counterclockwise, push it to the delivery pipes. Install
the eight injectors.
(d) Position the injector connector outward.
(e) Place the eight insulators and four spacers in position on the intake manifold.
FI±54
EFI SYSTEM
± Fuel System (Injectors)
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