WESTLAKE VILLAGE, Calif. — Diesel engine competitors Caterpillar and Cummins both ranked highest in satisfying customers with heavy-duty truck engines and transmissions, according to the J.D. Power and Associates 2007 Heavy-Duty Truck Engine/Transmission Study.

The study, now in its 11th year, measures customer satisfaction with engines in two-year-old heavy-duty trucks by examining four vital engine factors. They are (in order of importance): engine quality (30%); engine performance (26%); engine cost of ownership (22%); and engine warranty (22%).

The 2007 study includes engines equipped in 2005 model-year trucks, the second model year impacted by the EPA’s diesel engine emission standards.

Cummins ranks highest in customer satisfaction in the heavy engine vocational segment with an overall index score of 750 on a 1,000-point scale. The company performs particularly well in the engine warranty, engine performance and cost of ownership factors. Caterpillar closely follows Cummins in the segment with a score of 747, performing particularly well in engine quality, J.D. Power notes.

Caterpillar ranks highest in customer satisfaction in the heavy engine pickup and delivery segment with an index score of 754, performing well across each of the four engine factors. Cat performs particularly well in the engine quality and engine performance factors.

The study also finds that heavy-duty truck maintainers are reporting fewer problems with their engines than they did in 2006 — although problem incidence remains much higher than with pre-emission regulation 2003 model- year trucks. Industry-wide, the average number of reported engine problems is 59 PP100 (engine problems per 100 vehicles) — down from an average of 70 PP100 in 2006, but still well above the average of 46 PP100 reported prior to the new emission standards.

Several engine components show year-over-year quality improvements in the 2007 study. Two of the biggest improvements are for fuel injectors and turbochargers, which experienced large declines in quality in the 2006 study. Problem mentions for each of these components have declined by nearly 50 percent in 2007.

The most frequently cited engine problem for a second consecutive year, however, is the exhaust gas recirculation (EGR) valve, which accounts for 17 percent of all engine-related problems reported — a slight increase compared to the 2006 study.

“We saw a large jump in problems from 2005 to 2006 as manufacturers introduced new technologies to meet the emissions regulations,” said Brian Etchells, senior research manager in the commercial vehicle group at J.D. Power and Associates. “New technologies always introduce the possibility for more problems, so we were not surprised to see that in 2006. As expected, in 2007, we’re now starting to see those problem counts gradually decline.”