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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.

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  • Don't shout at us, it's rude...
    – Solar Mike
    Commented Nov 30, 2017 at 8:50
  • I've edited your question to make it easier to read and to remove all the unnecessary "shouting"
    – motosubatsu
    Commented Nov 30, 2017 at 9:11
  • If you can try and provide us with some more info - such as the total mileage of the car, when the plugs were last changed and what this "valve job" entailed.
    – motosubatsu
    Commented Nov 30, 2017 at 9:11
  • Can you repeat the compression test on Number 4 with a teaspoon full of engine oil down the spark plug hole please? If the compression temporarily improves, the problem is with the bottom end (piston ring, etc...) but if there is no change, the problem list in the head (valves, etc...)
    – Steve Matthews
    Commented Nov 30, 2017 at 13:05

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The low compression reading on cylinder four is pretty damning - there are a few things that could be at the root of this.

  • Leaking or sticking valve
  • Piston ring failure
  • Head gasket failure

The first two would be where I'd probably put my money since a head gasket failure would probably manifest additional symptoms and you don't mention anything else.

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