The Car Care Clinic with the Dr John

95 Chevy Cavalier - misfiring when damp conditions

Michelle in Kidderminster

Question

My 95 Chevy Cavalier has a problem when it's damp outside, it seems like it’s misfiring. I was wondering if you had any idea what would cause that to happen.

Answer

The solution to your wet weather misfiring problem should be easy to correct. From your description, it sounds as if the there is a spark plug wire that is starting to fail (as in leaking spark). The largest part of a spark plug wire (about 90%) is insulation to keep the spark (electricity) contained and heading in the right direction. The under hood environment of any vehicle is harsh. From the day the engine first starts, the insulation of the spark plug wires are under attack from this environment. As time goes on the insulation degrades or is damaged. The spark (electricity) is always looking for a shortcut and once the insulation of the spark plug wire degrades enough, the spark will find a new path. A fine mist of water is just the needed ingredient to allow the spark to travel a different direction, other than to the spark plug, on a marginal spark plug wire. A new spark plug wire set should be the fix Michelle

Good Luck!
Dr. John