One problem related to engine knocking noise has been reported for the 1998 Ford Ranger. The most recently reported issues are listed below.
Engine knocking, diagnosed as carbon build up, carbon remover added, engine seized, dealer replaced engine, 9000 miles on second engine. Same knocking noise is present. Ford service bulletin recommends same treatment as previously done. The bulletin also suggested revving engine to 3000 rpm on daily basis. I am concerned about long term affect carbon build up will have on the engine. Ford does not have a solution for this problem.