Ten months after launching a new diesel engine for heavy-duty pickup trucks, Ford faces a chorus of quality complaints from owners who are among the company's most loyal customers, Reuters reported. The 6-litre Power Stroke diesel V8, built by a unit of Navistar for Ford, commands nearly half the US market for diesel pickups but a range of problems and repeat trips to dealerships for repairs has left some owners upset, threatening Ford's efforts to rebuild a reputation for quality vehicles, the news agency added.