Camshaft Timing

• Wrong camshafts timing marks, a factory fault, causes continuous misfiring that is hard to diagnose in a 1999 Cougar engine, explains AA1Car.com. Replacing the timing chain installed using the timing marks will damage the engine, warns Mercury Problems, a technical service bulletin.
  
  

Spark Plugs and Related Problems

• The 4-cylinder engine misfires due to a loss of spark caused by the coil voltage's failure to jump the electrode gap due to worn or damaged spark plugs. It may also be due to a dirty or dead fuel injector and air leaks that cause a bad air-fuel mixture and compression loss, explains AA1Car.com.
  
  

Warning and Recommendations

• Mercury Problems recommends having repairs and maintenance handled at recognized service centers. The misfiring may result in continuous misfiring, which is bad for the engine, warns AA1Car.com.