Find Your Plug DENSO Global Part Number chart
DENSO Logo
DENSO SPARK PLUGS DENSO GLOBAL
HOME Topics Photo Gallery Movie collection Links
CONTENTS
Find Your Plugs
Reference
Part Number Chart
IRIDIUM POWER
Features
Structure
Linenup
Specifications
IRIDIUM TOUGH
Features
Structure
Linenup
Specifications
IRIDIUM PLUS
Features
Specifications
IRIDIUM POWER
Features
Structure
Linenup
Specifications
Basic_Knowledge
Plugs Configrations
 Plugs Specifications
Q & A
IRIDIUM POWER Q&A
IRIDIUM TOUGH Q&A
TECH Q&A
 Sales Companies
Cross Reference
Basic Knowledge
Spark and Ignition
Diagnosing the state of the spark plugs is an effective method for elucidating the cause of engine troubles.
Normal

The insulator leg section has light gray or tan deposits and slight electrode erosion.
Trouble
The flowing trouble can be caused by engine defects.
Engine trouble

Case 1 Case 2
· Starting defect
· Misfiring when idling
· Misfiring during normal running
· Misfiring only when running at high speed or when accelerating suddenly
Case 3 Case 4
· Loss of power when running at high speed or under high load Piston breakdown
· Trouble other than with the engine
Spark plug state

Case 1
· Starting defect
· Misfiring when idling
· Misfiring during normal running
diagram

[Appearance]
The insulator foot section and electrode section are covered with dried, soft black carbon.
[Results]
Poor starting, misfiring, acceleration defect.
[Cause]
Repeated short-distance driving (driving with the engine cool), incorrect choking (overly rich air-fuel mixture), injection timing delay, plug heat range too high.
diagram

[Appearance]
The insulator section and electrode section is black and lustrous with wet oily deposits.
[Results]
Poor starting and misfiring.
[Cause]
Oil leaking due to piston ring, cylinder, or valve guide wear (occurs easily to new engines and engines that have just been overhauled), high oil content in air-fuel mixture.(2-stroke engines)
diagram

[Appearance]
The spark plug is wet with gasoline immediately after it is removed, but it soon dries off.
[Results]
Poor starting and misfiring.
[Cause]
The air-fuel ratio is too rich and is not igniting. (Among the ways this can happen is if the driver presses the accelerator over and over while starting the vehicle.)
[Handling]
Remove all the spark plugs, crank the starter motor to bring fresh air into the cylinder and make the air-fuel ratio leaner.
diagram

[Appearance]
The center and ground electrodes are rounded and the gap has become too wide.
[Results]
Poor starting and acceleration.
[Cause]
Inadequate maintenance. (spark plug has exceeded its service life.)
diagram

[Appearance]
The gap is wider than appropriate.
[Results]
Poor starting and acceleration.
[Cause]
The gap is inappropriate; the wrong spark plug was selected. [Handling]
Remove all the spark plugs, crank the starter motor to bring fresh air into the cylinder and make the air-fuel ratio leaner.
diagram

[Appearance]
Insulator cracked
[Results]
Shorts due to insulation defect, causes poor idling and misfiring during acceleration.
[Cause]
Spark plug removed/installed incorrectly. (spark plug turned too far with spark plug wrench, excess tightening torque, or other inappropriate work.)
[Handling]
Remove all the spark plugs, crank the starter motor to bring fresh air into the cylinder and make the air-fuel ratio leaner.
Case 2
· Misfiring only when running at high speed or when accelerating suddenly
diagram

[Appearance]
The insulator leg section has yellow or yellowish-brown burnt on deposits or is covered with a glossy surface.
[Results]
Misfiring during rapid acceleration or under high load, but no problem in normal running.
[Cause]
Use of gasoline with much lead.
Case 3
· Loss of power when running at high speed or under high load
· Piston breakdown
diagram

[Appearance]
The insulator leg section is scorched extremely white with small black deposits. Rapid electrode wear.
[Results]
Loss of power when running at high speed or under high load.
[Cause]
Spark plug incorrectly tightened, engine cooling problem, ignition timing too early, spark plug heat range too low, severely abnormal combustion.
diagram

[Appearance]
The center electrode or ground electrode is melted or scorched. There are spots on the insulator leg section and deposits of aluminum or other metal powder.
[Results]
Power loss due to engine damage.
[Cause]
Often this is due to overheating; pre-ignition is a phenomenon in which combustion occurs before ignition.
The plug heat range is too low, the injection timing is too advanced, etc.
diagram

[Appearance]
The insulator leg section is cracked or broken.
[Results]
Misfiring
[Cause]
Severely abnormal combustion, lack of attention to gap adjustment.
diagram

[Appearance]
Housing installation screw section melting.
[Results]
Power loss due to engine damage.
[Cause]
Incorrect spark plug tightening.
diagram

[Appearance]
The electrode is bent and the insulator leg section is broken. Indentations are sometimes seen on the electrode.
[Results]
Misfiring.
[Cause]
The spark plug thread reach is too long for the engine head or there is some kind of foreign matter (a small bolt, nut, or the like) in the combustion chamber.
diagram

[Cause]
Overheating of the ground electrode and severe engine vibration.
Case 4
· Trouble other than with the engine
diagram

[Appearance]
Brown deposits on the insulator directly above the housing
[Results]
No impact on the spark plug performance
[Cause]
This occurs due to electrical stress in the air near the insulator. (This is not a spark plug gas leak, for which it is sometimes mistaken.)


Contact Us |  Sitemap |  Privacy Policy |  Terms of Use | 

Copyright (C) DENSO CORPORATION. All rights reserved.