 |
| Use Spark Plugs to Diagnose Problems |
|
|
|
Looking at spark plug firing tips can indicate if your engine has a problem that needs correcting. They reflect the performance of a well tuned or poorly maintained engine.
Even though spark plugs are easily replaced, inexpensive and immediately improve engine performance, they are often ignored until they cause serious performance problems. Bad plugs can cause over heating, rough running, power loss and even engine failure. Check your spark plugs regularly and use this chart as a guide to spot performance problems. |
|
 |
|
|
|
1. Normal |
|
|
|
 |
|
|
2. Normal with red coating
CAUSE: Red coating resulting from fuel additive in unleaded fuel. |
|
|
 |
|
|
3. Fuel Fouled
CAUSE: Faulty choke - overly rich fuel mixture, ignition problems or plug heat range too cold. |
|
|
 |
|
|
4. Detonation
CAUSE: Over advanced timing, low octane fuel. |
|
|
|
 |
|
5. Worn Plug
CAUSE: Plug used beyond its service life. Need to replace. |
|
|
 |
|
|
6. Glazing
CAUSE: Melting lead deposits - Plug too hot at high speeds. |
|
|
 |
|
|
7. Carbon Fouled
CAUSE: Plug heat range too cold - extended low speed driving. |
|
|
|
 |
|
|
8. Pre-ignition
CAUSE: plug heat range too hot - over advanced timing - air/fuel mixture too lean.. |
|
|
 |
|
|
9. Lead Fouled
CAUSE: Use of leaded fuel. |
|
|
 |
|
|
10. Oil Fouled
CAUSE: Poor oil control - worn rings, worn valve guides and valve seals. |
|
|
|
|
Courtesy of Autolite |
|
|
|
|