Fiesta 1100 K reg with about 85000 on the clock.
A friends car was missing and after investigation I found one plug not firing. I removed this and replaced with a new plug. I found that the plug I removed had accumulated some oil and this was stopping it firing.
The car then seemed to run fine. After about a week and 300 miles the car was again missing on the same plug. I noticed that there was oil around the plug hole above the plug. The engine did seem a bit oily and again the plug I removed had a certain amount of oil stopping it from firing.
I checked the rocker cover nuts and these were barely hand tight. The missing plug is the one near the gearbox end under the filler cap. I therefore tightened all the rocker cover nuts.
My question is could oil be running down the engine and into the spark plug hole and then down the threads of the plug finally causing the plug to fail to fire or is it more likely that there is an oil ring problem on the piston. Could the piston be pushing oil up past the spark plug? Incidently the engine was low on oil, on it's previous visit I had topped it up so I estimate it used about 1-2 pints in
300 miles. The exhaust however shows no great oily smoke.Having done a large mileage in another fiesta I know these engines are virtually indestructable I'm reluctant to think it is the oil ring on the piston. I'm waiting to see how the car is after a further week or so.
Any suggestions here please? Would an oil ring change be a relatively quick job or is it major engine dismantle?