ECU LEXUS SC400 1991 Service Repair Manual

EXHAUST GAS RECIRCULATION (EGR) SYSTEM
DESCRIPTION
To reduce NOx emission, part of the exhaust gases are recirculated through\
the EGR valve to the intake
manifold to lower the maximum combustion temperature.
OPERATION
Coolant Temp.ConditionEGR ValveExhaust Gas
Below 53 5C (127 5F)±CLOSEDNot recirculated
Above 55 5C (131 5F)(a)Idling, Deceleration, Neutral,
Low air volume, High Engine speedCLOSEDNot recirculatedAbove 55 C (131 F)
Except (a)OPEN*Recirculated
* The ECU calculates the appropriate number of steps according to the in\
take air volume and the engine speed, then
drives the stepping motor to maintain the EGR volume at a level appropri\
ate to the driving conditions.

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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±15
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wWhen replacing timing belt tensioner only:
To avoid meshing of the timing pulley and timing belt,
secure one of them with string. And place matchmarks
on the timing belt and RH camshaft timing pulley.
Alternately loosen the 2 bolts, and remove them, the belt ten-
sioner and dust boot.
29. DISCONNECT TIMING BELT FROM CAMSHAFT TIMING PULLEYS
(a) Using SST, loosen the tension spring between the LH and RH
camshaft timing pulleys by slightly turning the LH camshaft
timing pulley clockwise.
SST 09278±54012
(b) Disconnect the timing belt from the camshaft timing pulleys.
30. REMOVE CAMSHAFT TIMING PULLEYS Using SST, remove the bolt and timing pulley. Remove the 2
timing pulleys.
SST 09278±54012
EG±54
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1UZ±FE ENGINE ENGINE MECHANICAL
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35. REMOVE CYLINDER HEAD COVERSRemove the 8 bolts, seal washers, cylinder head cover and
gasket. Remove the 2 cylinder head covers.
36. IF NECESSARY, REMOVE SEMI±CIRCULAR PLUGS
37. REMOVE CAMSHAFTS
NOTICE: Since the thrust clearance of the camshaft is small,
the camshaft must be kept level while it is being removed. If the
camshaft is not kept camshaft is not kept level, the portion of
the cylinder head receiving the shaft thrust may crack or be
damaged, causing the camshaft to seize or break. To avoid
this, the following steps should be carried out.
A. Remove exhaust camshaft from RH cylinder head
(a) Boring the service bolt hole of the driven sub±gear upward by turning the hexagon wrench head portion of the exhaust
camshaft with a wrench.
(b) Secure the exhaust camshaft sub±gear to the drive gear with
a service bolt.
Recommended service bolt: 6 mm for thread diameter
1.0 mm for thread pitch
16 ± 20 mm (0.63 ± 0.79 in.) for bolt length
HINT: When removing the camshaft, make sure that the tor-
sional spring force of the sub±gear has been eliminated by
the above operation.
(c) Set the timing mark (1 dot mark) of the camshaft driven gear at approx. 10
angle by turning the hexagon wrench head
portion of the exhaust camshaft with a wrench.
EG±86
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1UZ±FE ENGINE ENGINE MECHANICAL
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C. Remove exhaust camshaft from LH cylinder head
(a) Boring the service bolt hole of the driven sub±gear upwardby turning the hexagon wrench head portion of the exhaust
camshaft with a wrench.
(b) Secure the exhaust camshaft sub±gear to drive gear with a service bolt.
Recommended service bolt:6 mm for thread diameter
1.0 mm for thread pitch
16 ± 20 mm (0.63 ± 0.79 in.) for bolt length
HINT: When removing the camshaft, make sure that the tor-
sional spring force of the sub±gear has been eliminated by
the above operation.
(c) Set the timing mark (2 dot marks) of the camshaft drive gear at approx. 15
angle by turning the hexagon wrench head
portion of the exhaust camshaft with a wrench.
(d) Alternately loosen and remove the 2 bearing cap bolts holding the intake camshaft side of the oil feed pipe to the
cylinder head.
(e) Uniformly loosen and remove the 8 bearing cap bolts in several passes, in the sequence shown.
(f) Remove the oil feed pipe, 4 bearing caps and ex haust
camshaft.
EG±88
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1UZ±FE ENGINE ENGINE MECHANICAL
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(e) Take out the front side of the floor carpet.
(f) Remove the 2 nuts and ECM protector.
(g) Remove the nut, and disconnect the ECM from the floorpanel.
(h) Disconnect the following connectors: (1) 2 connectors from ECM
(2) Connector from ABS & TRAC ECU
(3) 2 connectors from TRAC ECU
(4) 4 connectors from connector cassette
(5) Connector from A/C control assembly
EG±146
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1UZ±FE ENGINE ENGINE MECHANICAL
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11. CONNECT ENGINE WIRE TO CABIN
(a) Push in the engine wire through the cowl panel.NOTICE: Be careful not to damage the engine wire. Tape
the engine wire.
(b) Install the engine wire retainer with the 3 bolts.
(c) Connect the following connectors: (1) 2 connectors to ECM
(2) Connector to ABS & TRAC ECU
(3) 2 connectors to TRAC ECU
(4) 4 connectors to connector cassette
(5) Connector to A/C control assembly
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1UZ±FE ENGINE ENGINE MECHANICALEG±195
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(e) Take out the front side of the floor carpet.
(f) Remove the two nuts and ECU protector.
(g) Remove the nut, and disconnect the engine & ECT ECU
from the floor panel.
(h) Disconnect the following connectors: (1) Two connectors from engine & ECT ECU
(2) Connector from ABS & TRAC ECU
(3) Two connectors from TRAC ECU
(4) Four connectors from connector cassette
(5) Connector from A/C control assembly
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ENGINE MECHANICAL Cylinder BlockEM±125
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(c) Connect the following connectors:(1) Two connectors to engine & ECT ECU
(2) Connectors to ABS & TRAC ECU
(3) Two connectors to TRAC ECU
(4) Four connectors to connector cassette
(5) Connector to A/C control assembly
(d) Install the engine & ECT ECU with the nut.
(e) Install the ECU protector with the two nuts.
(f) Install the floor carpet.
EM±170
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ENGINE MECHANICAL Cylinder Block
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Troubleshooting
If the CO/HC readings do not comply with regulations, pre-
form troubleshooting in the order given below.
(a) Check oxygen sensor operation.(See page FI±73)
(b) See the table below for possible cause, and then inspect
and correct the applicable causes if necessary.
 CO HC Symptoms Cause
 Normal High Rough idle 1. Faulty ignition:
     Incorrect timing
     Fouled, shorted or improperly gapped plugs
 Open or crossed high±tension cords     Cracked distributor cap    2. Incorrect valve clearance    3. Leaky EGR valve    4. Leaky intake and exhaust valves
    5. Leaky cylinder
 Low High Rough idle 1. Vacuum leak:
   (Fluctuating HC reading)  PCV hose
     EGR valve
     Intake manifold
     Air intake chamber
 Throttle body     ISC valve     Brake booster line    2 Lean mixture causing misfire High High Rough idle 1. Clogged air filter
   (Black smoke from exhaust) 2. Faulty EFI system
     Faulty pressure regulator
     Clogged fuel return line
     Defective engine coolant temp. sensor
     Defective intake air temp. sensor
     Faulty ECU
 Fault injectors     Faulty throttle position sensor     Faulty volume air flow meter
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ENGINE MECHANICAL Idle and/or 2,500 rpm CO/HC CheckEM±21
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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
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ENGINE MECHANICAL Idle and/or 2,500 rpm HC/CO
Concentration Check MethodEM±29
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