(or How to Change a #5 Injector) Solving the mystery of a vehicle’s mechanical problem can require some lengthy detective work—as demonstrated in this repair that I call “The Case of the $942 Fuel Filter.” The initial complaint by the Ram Turbo Diesel’s owner provided me with scant evidence for solving the problem: “It runs good,” he said, “for a while after I change the fuel filter, but it has low power.” I doubted that the fuel filter was the culprit. But I had little to go on. This would…