I have a 1997 mercury grand marquis and supposedly I might have a blown head gasket. I took my vehicle to pep boys for an inspection of the problem. They claimed their was no compression in cylinders 7 and 8 (misfire) and that it might be a possible head gasket / head and that they couldnt tell for sure. Another local mechanic said it could be the distributor / pack where (spark plug wiring connects) What should I do and how much do these repair run up to for a car such as the gran marquis?—> Notable symptoms: Muffler releases gray smoke but now it appears to be bluish gray. Lack of performance. At times the vehicle may stop when going uphill or going very slow.