Ford Motor Co. is working to develop its own diesel engines for use in its F-Series Super-Duty pickups, says the auto maker's current diesel supplier, Navistar International Inc.

In a legal filing, Navistar claims Ford does not intend to purchase diesel engines from the supplier after '09, although the contract between the two companies is binding through 2012. Navistar is seeking $2 billion in damages from Ford.

A copy of the counter-complaint obtained by Ward's says Navistar has “information and belief” that “Ford has been working on a program to design and manufacture its own diesel engines for model-year 2010.”

Navistar bases its claim, in part, on communication with its suppliers.

Ford's apparent decision to back out of its deal has caused problems that go beyond Navistar, the engine supplier says.

“Ford not only breached the agreement but has also interfered with (Navistar's) relationships with its own suppliers, who are worried about the consequences should Ford improperly refuse to buy diesel truck engines after 2009.”

A Ford spokeswoman says there is “no basis” for Navistar's allegations.