The problem COULD be due to a defective valve guide seal on the #4
intake valve stem. In that instance lube oil would be sucked down the
valve stem into the intake port where as Tiger previously suggested the
oil gets "coked" or carbonized preventing the valve from fully closing -
thus low compression. A dribbling #4 fuel injector could also be the cause.
You CAN drive the car until it fails an emissions test. The engine won't
If it were my car I'd try the following, in this order of cost and
Install a new or rebuilt fuel injection nozzle in #4 cylinder. $60
Sequentially add two or three cans of Techron to the fuel. $8 each
Drive it a month or so.
If no improvement have your mechanic replace the valve stem seals on
#4's valve stems. Guess about $250.
Thereafter, some doses of Techron to eliminate the coking in the valve's
If the problem still persists the cylinder head will need to be removed.