The culprit is oil collecting in the cylinder and not being burnt off. Generally it is caused by 1) leaky valve seals, 2) worn rings, 3) leaking head gasket.
The first check should be a compression test to verify if the rings or heads are leaking. If they are fine the only thing left is the valve seals. Not an easy fix but can be done by a home mechanic with some effort.
Wear. Fouled. Cracked.
Fouling spark plugs can happen when the tip temperature is insufficient to burn off carbon, fuel, oil or other deposits and causes spark to leach to metal shell...no spark across plug gap will cause a misfire. Wet-fouled spark plugs must be changed as they won't fire. Dry-fouled spark plugs can sometimes be successfully cleaned by bringing the engine up to the operating temp.
possible fouled spark plugs, bad fuel. check both and if both are good, get back to me.
Faulty/fouled spark plugs or spark plug wires. I had this problem and a set of new wires fix it.
if the spark plugs are black because your car is running too rich. your plugs are fouled.
intake manifold gasket is leaking and water is getting on the plugs, plastic piece melts and causes leak
Yes, fouled spark plugs can cause engine shaking, and loss or power. I'm not sure about knocking but I'd guess that too.
Absolutely. Worn plugs or carbon-fouled plugs can cause an engine to not start.
Possible wrong heat range of plug. Make sure you have the right plugs for the vehicle.
no The starter should engage whether the plugs are fouled or not. However, the engine may not start if enough plugs are fouled. If you feel that you have flooded the engine or fouled the plugs you may need to clean them before it will start. If you have caused the carburetor float level or other settings to be significantly changed, the engine will flood and it will not start.
Spark plugs do not loose power, rather, they become worn and erroded. On occasion they may also become fouled, indicating a mechanical or fuel problem.
No spark from coil, bad plug wires, or bad plugs.