Lexus SC300 / Lexus SC400. Manual — part 523
SYSTEM CIRCUIT
OPERATION
To maintain the most appropriate ignition timing, the ECU sends a control signal so that the igniter sends
current to the ignition coil and the spark plugs produce a spark.
IG–4
–
IGNITION SYSTEM
System Circuit, Operation
PREPARATION
SST (SPECIAL SERVICE TOOLS)
RECOMMENDED TOOLS
EQUIPMENT
Part Name
Note
Engine tune–up tester
Ignition timing
Megger (Insulation resistance meter)
Spark plug
Spark plug cleaner
Torque wrench
16 mm plug wrench
–
IGNITION SYSTEM
Preparation
IG–5
ON–VEHICLE INSPECTION
SPARK TEST
CHECK THAT SPARK OCCURS
(a) Remove the No.3 timing belt covers.
(See steps 2 to 8 on pages
to 13)
(b) Disconnect the high–tension cords (from the ignition
coils) from the distributor caps.
(c) Hold the end about 12.5 mm (0.50 in.) from the body
ground.
(d) Check if spark occurs while engine is being cranked.
HINT: To prevent gasoline from being injected from injectors
during this test, crank the engine for no more than 1–2 se-
conds at a time.
If the spark does not occur, perform the test as follows:
(e) Reconnect the high–tension cords to the distributor
caps.
(f) Reinstall the No.3 timing belt covers.
(See steps 5 to 11 on pages
IG–6
–
IGNITION SYSTEM
On–Vehicle Inspection
INSPECTION OF HIGH–TENSION CORDS
1.
REMOVE HIGH–TENSION CORDS
(See steps 1 to 9 on pages
2.
INSPECT HIGH–TENSION CORD RESISTANCE
Using an ohmmeter, measure the resistance.
Maximum resistance: 25 k
per cord
If the resistance is greater than maximum, replace the high–
tension cord.
3.
REINSTALL HIGH–TENSION CORDS
(See steps 4 to 13 on pages
INSPECTION OF SPARK PLUGS
NOTICE:
•
Never use a wire brush for cleaning.
•
Never attempt to adjust the electrode gap on used spark
plug.
•
Spark plug should be replaced every 100,000 km (60,000
miles).
1. DISCONNECT HIGH–TENSION CORDS FROM SPARK
PLUGS (See steps 1 to 9 on pages
2. INSPECT
ELECTRODE
Using a megger (insulation resistance meter), measure the
insulation resistance.
Correct insulation resistance: 10 M
or more
If the resistance is less than specified, proceed to step 4.
HINT: If a megger is not available, the following simple meth-
od of inspection provides fairy accurate results.
(Simple Method)
(a) Quickly race the engine to 4,000 rpm five times.
(b) Remove the spark plug. (See step 3)
(c) Visually check the spark plug.
If the electrode is dry. . . . . Okay
If the electrode is wet . . . . . Proceed to step 4
(d) Reinstall the spark plug.
(See step 7 on page
3. REMOVE
SPARK
PLUGS
Using a 16 mm plug wrench, remove the spark plugs.
–
IGNITION SYSTEM
On–Vehicle Inspection
IG–7
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