WASHINGTON (Reuters) -The National Highway Traffic Safety Administration (NHTSA) said on Monday it was upgrading and expanding its investigation into 708,000 Ford Motor sport utility vehicles and trucks over catastrophic engine failures tied to a faulty valve. The agency says under normal driving conditions vehicles without warning may experience a loss of power due to catastrophic engine failure related to a potentially faulty valve in 2.7 L and 3.0 L EcoBoost engines.