One problem related to gas recirculation valve (egr valve) has been reported for the 1998 Ford E-150. The most recently reported issues are listed below.
1998 (manufactured 1997) Ford 4. 2 liter engine blew main head gasket - engine froze up. Replaced with remanufactured engine - combustion too high - pings - Ford refuses to install another engine. Carbon build up - valves, rings, crankshaft, egr and catalytic converter will all be damaged if not corrected. Dealer had tried on 5 occasions - Ford continues to deny approval for another engine.