Cadillac Repair: 1997deville, head gasket leak, compression check

Question
hello ,just the last week my 97 deville has been running rough ,then the service engine lite came on  .i took it to autozone.they ran a test and said number 7 was misfiring any clues were to start they said could be a plug or wire or injector,any clues,thank you

Answer
Im gonna save you some money, so first replace the spark plug and check the ignition cable it may be neccessary to replace it, then run some lucas injector cleaner. If this doesnt work do a compression check on #7 cylinder and if the compression is lower than 40% of the other cylinders (which is probably 120-160 psi) then you may have a head gasket leak.