Fouled spark plugs

I am assuming it is oil fouled rather than fuel fouled. Oil fouling is usually due to valve stem seal leakage. Most engines have the oil return on the cylinder head at the rear. When the engine is shut off, some oil pools at the rear of the head. If the valve guide seals are worn, then the oil will leak around the stem of the #4 valve and eventually foul the plug. If there are no real issues with the engine other than this one, it is usually best to keep a clean plug or two available and swap out the plug periodically when fouling is detected. Then clean the fouled one and keep for reuse later. If it is happening too often, getting the cylinder head reconditioned is a good idea.

A Bank 1 O2 sensor error usually means that you have a fouled spark plug, a stuck fuel injector, or a bad spark plug wire; not necessarily that the sensor itself has gone bad. (It is an "out of range" error.)

Hi Aadil:
The spark plug that is misfiring should tell the story. Is it oil fouled? Bad rings or valve seal. Is it carbon fouled? Electrodes fried? Wet looking? Maybe a bad plug wire and it's not firing properly?
What kind of engine?
See if you can isolate the problem and we'll try to be more specific with help.

Well it depends on the color of smoke if it's WHITE; it could be a blown head gasket (check coolant levels and then oil to see if it is milky looking) BLUE: could be burning oil, which could result to fouling plugs (check spark plugs for fouling) BLACK; too much fuel flooded (check spark plugs for fouling)

the next time it fouls check the plug when you take it out, if it is covered with oil then you may have a broken ring on the cylinder that is allowing oil to pass through to the combustion chamber and fouling the plug. Or the valves pay be letting oil drain in past the valve seats.

Hi Dale,

Several factors can contribute to spark plug fouling:

- The air/fuel ratio may be too rich as a result of incorrect carburetor adjustment or a poorly performing fuel injection system.
- Worn piston rings or valve seals may allow too much oil to leak into the combustion chamber, leading to oil fouling.
- The ignition system may not be performing properly.
- Prolonged idling or continuous low-speed driving may keep the spark plug from reaching its optimum operating temperature. Using too cold a spark plug can lead to the same problem.
- A dirty air cleaner can create a too-rich condition which can lead to fouling.

Have each of the above checked and corrected.

Fuel, oil and carbon fouling can all be the result of different causes but, once a spark plug is fouled, it will not provide adequate voltage to the firing tip and that cylinder will not fire properly.

In many cases, the spark plug cannot be cleaned sufficiently to restore normal operation. Hence, I always recommend that a plug be replace, once it becomes fouled.

Cheers,

Scott


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Hi Dale,

Several factors can contribute to spark plug fouling:

- The air/fuel ratio may be too rich as a result of incorrect carburetor adjustment or a poorly performing fuel injection system.
- Worn piston rings or valve seals may allow too much oil to leak into the combustion chamber, leading to oil fouling.
- The ignition system may not be performing properly.
- Prolonged idling or continuous low-speed driving may keep the spark plug from reaching its optimum operating temperature. Using too cold a spark plug can lead to the same problem.
- A dirty air cleaner can create a too-rich condition which can lead to fouling.

Have each of the above checked and corrected.

Fuel, oil and carbon fouling can all be the result of different causes but, once a spark plug is fouled, it will not provide adequate voltage to the firing tip and that cylinder will not fire properly.

In many cases, the spark plug cannot be cleaned sufficiently to restore normal operation. Hence, I always recommend that a plug be replace, once it becomes fouled.

Cheers,

Scott


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If the insulator was cracked the plug would have been misfiring, unless it was broken while trying to remove it. If this oil fouling is an ongoing problem, and you have to keep changing the plug, buy a spark plug that is designed to fire when oil fouling is a problem. You may have to order one from a part catalog, such as JC Whitney. This would keep you going until you can get the problem repaired..

Fouling occurs when the spark plugs' firing tip becomes coated with excessive fuel, oil, or combustion deposits so that it is unable to produce a spark. A plug can become fouled from continuous low speed driving, improper spark plug heat range (too cold), improper timing (over-retarded), too rich an air/fuel ratio or an oil leak into the combustion chamber. A variety of self-cleaning features are designed into most plugs to reduce fouling.

Replace the spark plugs and wire set and add fuel injector cleaner in the gas tank for the next three fill up's. If money is tight try swapping the spark plug wire with another wire and see if the missfire moves, but before you do that inspect the spark plug's condition. Remove the spark plug to see if it's fouled with carbon which is a run rich condition and if there was detonation the plugs will have a worn or damaged electrode. Keep me posted, be glad to help.