My Cavalier appears to have a misfire on cylinder 4.
A compression test gave readings of 120, 120, 122, and 60 suggesting a loss of compression on that cylinder and the spark plug keeps fouling with a black build up of carbon on it. The plug is dry with no sign of gas or oil just the carbon deposits. The No.4 plug had a valve job done approx 30,000 miles ago.
Any ideas what may have happened to my engine and what I can do to try and resolve the issues?
Additional info - I've perform oil changes every 3,000 miles and there is no history of overheating. The car is an automatic and is driven gently.