The EPA is investigating whether seven major truck-engine manufacturers have been improperly encouraging customers to pre-buy engines before October, when clean-air regulations are scheduled to take effect, The Chicago Tribune reported. According to The Tribune, an unnamed source at EPA said the diesel manufacturers, including Caterpillar Inc. and Cummins Inc., are prohibited from encouraging pre-buying under terms of a 1998 consent decree. The story said EPA sent a letter to each of the seven engine manufacturers that signed the decree asking if they have taken any action to encourage pre-buying, and requests extensive documentation in the form of copies of written communication with customers and similar information. Cummins hasn't encouraged any pre-buying of its engines and will comply with the EPA's request for information, a spokesman for the company told The Tribune."We've got an EPA-compliant engine, and no reason to encourage a pre-buy," he said pointedly. Cummins, which is the only enginemaker to receive formal EPA certification for an Oct. '02 engine at this point, will enjoy "an advantage in the market after Oct. 1," he told The Tribune.