Step
| Action
| Value(s)
| Yes
| No
|
1
|
- Remove the spark plug from the engine.
- Note which cylinder the plug is from.
Do you see a brown to grayish tan deposit with a slight electrode wear?
| --
|
Go to Step 2
|
Go to
Step 3
|
2
|
- This is normal wear.
- Clean, regap and reinstall the plug.
- Tighten the plug.
Is the repair complete?
| --
| System
OK
| --
|
3
| Do you see dry, fluffy,
black carbon deposits?
| --
|
Go to Step 4
|
Go to Step 5
|
4
|
- This indicates poor ignition output.
- Check distributor to coil connections.
- Correct all connections, if necessary.
Is the repair complete?
| --
| System
OK
| --
|
5
| Do you see wet, oily
deposits with very little electrode wear?
| --
|
Go to Step 6
|
Go to Step 7
|
6
|
- This may result from:
| • | "Break-in" of a new or recently overhauled engine |
| • | Excessive valve stem guide clearances |
| • | Worn intake valve seals |
- Degrease, gap and reinstall the spark plugs.
Is the repair complete?
| --
| System
OK
| --
|
7
| Do you see red, brown,
yellow and/or white colored coatings on the insulator?
| --
|
Go to
Step 8
|
Go to Step 9
|
8
|
- These are the by-products of combustion.
- Clean, regap, and reinstall the spark plugs.
- Replace the spark plugs, if the insulator is heavily coated.
Is the repair complete?
| --
| System
OK
| --
|
9
| Are there heavy deposits
of dark colored coatings, especially on the side of the plug facing the intake
valve?
| --
|
Go to Step 10
|
Go to
Step 11
|
10
|
- This is the result of leaking valve seals.
- Check the valve seals.
- Replace valve seals if necessary.
- Clean, regap, and reinstall the spark plugs.
Is the repair complete?
| --
| System
OK
| --
|
11
| Is there a shiny,
yellow glaze coating on the spark plug insulator?
| --
|
Go to Step 12
|
Go to Step 13
|
12
|
- These are the melted by-products of combustion.
- Avoid wide open throttle after long periods of low speed operation.
- Replace the spark plugs.
Is the repair complete?
| --
| System
OK
| --
|
13
| Are the insulator
tips blistered or burned and the electrodes are badly eroded?
| --
|
Go to
Step 14
|
Go to Step 15
|
14
|
- This is the result of overheating.
- Check the spark plug heat range.
- Replace the spark plugs if heat range is incorrect.
Is the repair complete?
| --
| System
OK
| --
|
15
| Are the insulator
tips broken or cracked?
| --
|
Go to Step 16
| System OK
|
16
| Replace the spark plugs.
Is the repair complete?
| --
| System
OK
| --
|
