One problem related to diesel engine has been reported for the 1998 Ford Explorer. The most recently reported issues are listed below.
I own a 1998 Ford Explorer. This vehicle has been making an awful knocking/rattle in the engine on start up. It has been doing this for about 6 months now. Unable to diagnose problem due to it only does it on cold start ups, once the engine has warmed up it tends to stop. However, after a cold start up it will rattle (sounds like a diesel engine), the rattle increases as I accelerate, however once vehicle has ran for about 10 miles it will go away. If vehicle is parked for an extended period of time then started up again then the noise will return.