88 Mustang GT Help

did you read the plugs? That will tell you which cylinder if you have a bad valve etc. change rotor cap - do a tune up The fuel pump is inside the gas tank, you changed that out? Why? change the O2 sensors read the codes out don't rev it up over 5500 ever if a daily driver. put in a new coil.

Is the check engine light on?

Go to your auto parts store and buy a Chilton's or Haynes repair manual for your 88 GT. Those books have pictures of plugs ranging from normal to detonated to rich, to lean, etc. Just compare the plugs from your car with the pictures. That book will also tell you where the O2 sensor is (exhaust manifold). I hope you saved the plugs when you changed them, and know which cylinder they were in. Also, did you gap the new plugs?

There is also a troubleshooting section in the back that gives suggestions for symptoms. Dave