From http://www.autonews.com/news.cms?newsId=3787
Ford spokeswoman Jennifer Flake declined to say why the V-6 diesel program is not viable.
There are several potential reasons:
Emissions: Though Navistar claims to have emissions technology that allows use of diesels in vehicles under 8,500 pounds gross vehicle weight rating, no other automaker or engine manufacturer has made a similar claim. General Motors, which is testing a V-6 version of the Duramax diesel, doesn't think it can make the engine meet existing and upcoming emission standards until low-sulfur diesel fuel becomes available in late 2006.
Performance: Navistar's V-6 has a displacement of 4. 5 liters. It may not deliver enough performance at certain speeds to satisfy sport-utility and truck buyers who crave high-horsepower engines.
Cost: The engine may be too expensive to produce and sell at a profit. The V-8 diesel versions of the Ford, GM and Dodge full-sized pickups add between $2,500 and $3,000 over the cost of a gasoline engine.
Appeal: Automakers are nervous about the potential of diesel engines. A recent study by the Chrysler group found that just 6 percent of buyers would consider a vehicle with a clean diesel engine - lower than those who would buy a vehicle with a navigation system. Automakers fear that buyers won't embrace diesels because of the bad image from the 1970s.