Isuzu KB P190. Manual — part 893

Engine Management – V6 – Service Operations

Page 6C1-3–48

2.22 Spark

Plugs

Service Precautions

1

Allow the engine to cool (to at least 50

°C) before attempting to remove spark plugs. Attempting to remove spark

plugs from a hot engine may cause the plug / cylinder head threads to bind, resulting in tearing of the alloy cylinder
head threads.

2

Clean the spark plug recess area before removing any spark plug. Failure to do so could result in engine damage
because of dirt or other foreign material entering the cylinder head or by the contamination of the cylinder head
threads. The contaminated threads may then prevent the correct seating of the new or replaced plug. If required,
use a thread chaser to clean the threads of any contamination where this is suspected.

3

Under no circumstances should the spark plug/s gap
be adjusted. If the gap is not within specifications,
replace the spark plug.

Figure 6C1-3 – 66

Remove

1

Turn the ignition switch off.

2

Remove the ignition coil/s, refer to 2.15 Ignition Coil.

3

Using a suitable spark plug socket, loosen the spark plug slightly and then re-tighten to break away any carbon
deposits on the threads.

Wear eye protection to avoid injury.

4

Loosen the spark plug once again one or two turns, then use compressed air to remove any foreign material that
may otherwise enter the combustion chamber.

5

Remove the spark plug (1).

6

Repeat as required for the remaining spark plugs.

N O T E

Place each spark plug in the same order as that
of removal. This will enable any abnormal spark
plug condition to be identified with the cylinder.

N O T E

If the spark plugs are removed for an indefinite
period before installation, plug the spark plug
openings to prevent foreign particle ingress.

7

Repeat steps 2 to 5 for the remaining spark plugs as
required.

Figure 6C1-3 – 67

Inspect

The spark plugs must not be re-gapped. If the gap of a spark plug is outside the specified range, replace the spark plug.
In addition, replace spark plugs that shows excessive dirt deposit or broken insulators.

Engine Management – V6 – Service Operations

Page 6C1-3–49

1

Replace any plug that has cracked and / or broken insulation or loose electrodes.

2

Inspect the spark plugs for defects. Refer to Analysis of Spark Plug Condition in this Section for identification of the
condition of spark plugs.

3

Ensure the threads are clean and in good order.

4

Use a round wire feeler gauge to check the spark plug
gap. If the gap is not within specifications, replace the
spark plug.

Spark plug gap. . . . . . . . . . ... 1.1 – 1.2 mm

Figure 6C1-3 – 68

Spark Plug Inspection

Poor Spark Plug Performance

A spark plug can perform poorly due to wear, dirt, carbon fouling, excessive electrode wear, a broken insulator or
excessive gap.

Worn or Dirty Plugs

Worn or dirty plugs can give satisfactory operation while the vehicle is idling, but break down under load.

This can cause:

•

poor fuel economy,

•

power loss,

•

acceleration loss,

•

difficult starting, or

•

poor engine performance.

Carbon Fouling

Carbon fouling is indicated by black carbon deposits. The black deposits are usually the result of slow-speed driving and
short runs. In these circumstances, the optimum engine operating temperature is seldom reached.

Fouling can also be caused by:

•

worn piston rings,

•

faulty ignition,

•

rich fuel mixture, or

•

spark plugs that are rated too cold.

Excessive Electrode Wear

This often indicates:

•

the engine is operating at high speeds,

•

the engine is operating at levels that are consistently greater than normal,

•

a plug that is rated too hot,

•

excessively lean fuel mixture, or

Engine Management – V6 – Service Operations

Page 6C1-3–50

•

plug/s overheating due to insufficient tightening (caused by combustion gases leaking past the threads).

Broken Insulator

Broken insulators are usually the result of improper installation or carelessness.

Breaks in the upper insulator can result from a poor fitting spark plug socket or impact. The cracked insulator may not
show up until oil or moisture penetrates the crack. The crack is often just below the crimped part of the shell and may not
be visible.

Breaks in the lower insulator often result from careless re-gapping and are usually visible.

This can also result from the plug operating too hot. For example, in periods of high speed operation or under heavy
loads.

Engine Management – V6 – Service Operations

Page 6C1-3–51

Analysis of Spark Plug Condition

Figure 6C1-3 – 69

Legend

1 Normal

2 Carbon

Fouled

3 Oil

Fouled

4

Deposit Fouling A

5

Deposit Fouling B

6

Deposit Fouling C

7 Detonation

8 Pre-ignition

9

Heat Shock Failure

10

Insufficient Installation Torque

Normal Operation (1)

Brown or greyish-tan deposits and slight electrode wear indicate correct spark plug heat range and mixed periods of high
and low speed driving.

Carbon Fouled (2)

Dry, fluffy black carbon deposits possibly due to poor ignition output, a weak coil, excessive idling or slow speeds under
light load. If spark plug temperatures remain too low for normal combustion, the deposits are not burned off.