[350HP930]

My car started to foul plugs around the 120K mile mark.

At first I assumed the worse such as cylinder damage or extremely bad valve guide wear.

After my engine break down I discovered that the problem was that the oil control rings on the pistons were completely coked up and had lost most of their tension. It was quite a reminder of how important those oil squeegees are on a piston when big oil squirters spraying the hell out of them.

You could be looking at anything as minor as this or something as serious as a broken piston and/or gouged cylinder or a really bad intake valve guide or seal.

Start with a compression and leakdown test. It will at least give you an idea of what kind of condition the cylinder is in.