Diagnosing a vehicle with obvious driveability symptoms is for the most part a cut and dried procedure. However, some symptoms are intermittent and are not always so obvious or so easily duplicated. When a vehicle is towed to your shop with a “cranks but will not start” complaint, you hope that it will remain in a no-start situation after it arrives so that you can quickly diagnose and repair the problem. After all, you can’t fix what isn’t broken. If the vehicle starts and runs fine after it is dropped off, you may spend hours trying to get the symptom to reoccur, without success.