Lexus SC300 / Lexus SC400. Service 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 

IG–11

 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–17

 to 19)

IG–6

–

 IGNITION SYSTEM

On–Vehicle Inspection

INSPECTION OF HIGH–TENSION CORDS

1. 

REMOVE HIGH–TENSION CORDS
(See steps 1 to 9 on pages 

IG–11

 to 14)

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 

IG–11

 to 19)

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 

IG–11

 to 13)

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 

IG–8

)

3. REMOVE 

SPARK 

PLUGS

Using a 16 mm plug wrench, remove the spark plugs.

–

 IGNITION SYSTEM

On–Vehicle Inspection

IG–7