Resistor type spark plugs with tapered seats are used. No gasket is needed on these plugs. These spark plugs are a High Efficiency (HE) spark plug that has a fine wire electrode, nickel plated shell and a platinum pad across from the electrode.
| • | Normal service is a mixture of idling, low speed, and high speed operation. |
| - | Occasional high speed driving is essential to good spark plug performance. |
| - | Increased combustion heat burns away excess carbon deposits, which accumulate from frequent idling or stop-and-go driving. |
| • | A broken upper insulator is usually the result of improper installation or carelessness when regapping the plug. |
| - | Broken UPPER insulators usually result from a poor fitting wrench or an outside impact. |
| - | The cracked insulator may not show up right away, but will as soon as oil or moisture penetrates the crack. |
| • | Broken LOWER insulators usually result from carelessness when regapping and generally are visible. |
| - | This type of break may result from the plug operating too hot, which may happen in periods of high-speed operation or under heavy loads. |
| - | When regapping a spark plug, always make the gap adjustment by bending the ground (side) electrode. |
| - | Always replace spark plugs that have broken insulators. |
| • | Corona discharge is a steady blue light appearing (in darkness) around the insulator, just above the shell crimp. |
| - | Do not mistake this for a shorted insulator. |
| - | This is visible evidence of a high-tension field. |
| - | This has no effect on ignition system performance. |
| - | This discharge repels dust particles. |
| - | This leaves a clear ring on the insulator just above the shell. |
| - | This is not evidence that combustion gases are escaping. |
Problem | Action | ||||||||||
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Brown to Grayish - Tan Deposits and Slight Electrode Wear | |||||||||||
The spark plug has normal wear. | Clean, regap, and reinstall the spark plug. Refer to Spark Plug Replacement in Engine Electrical. | ||||||||||
Dry, Fluffy Black Carbon Deposits | |||||||||||
The spark plug has poor ignition output. | Inspect the spark plug wires and coil connections. | ||||||||||
Wet, Oily Deposits with Very Little Electrode Wear | |||||||||||
Break-in of a new or recently overhauled engine. | Degrease, clean, and reinstall the spark plugs. Refer to Spark Plug Replacement in Engine Electrical. | ||||||||||
The clearances of the valve stem guides are excessive | Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. | ||||||||||
The intake valve seals are worn. | Replace the valve seals. Refer to Valve Stem Oil Seal and Valve Spring Replacement in Engine Mechanical. | ||||||||||
Colored Coatings on Insulator/Engine Misfires | |||||||||||
DEFINITION: The spark plug has red, brown, yellow and white colored coatings on the insulator. The engine misfires intermittently under severe operating conditions. | |||||||||||
The coatings are the by-products of combustion |
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Heavy Colored Coating Deposits | |||||||||||
DEFINITION: Heavy colored coating deposits on the portion of the spark plug that projects into the chamber, and on the side facing the intake valve. | |||||||||||
The valve seals are leaking (if this condition is found in only one or two cylinders). |
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Shiny Yellow Glaze Coating on Insulator | |||||||||||
The coating is caused from the melted by-products of combustion. |
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Burned or Blistered Insulator Tips and Badly Eroded Electrodes | |||||||||||
The spark plugs are overheating. |
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Broken or Cracked Insulator Tips | |||||||||||
The plugs show heat shock from a sudden rise in tip temperature under severe operating conditions. | Replace the spark plugs. Refer to Spark Plug Replacement in Engine Electrical. | ||||||||||
The spark plugs are improperly gapped. | Gap the plugs to specification. Refer to Spark Plug Replacement in Engine Electrical. | ||||||||||
