(FORTUNE Magazine) – When it comes to grading quality, J.D. Power & Associates is to cars and trucks what government inspection is to meat. Customer surveys that the California market research firm conducts after the first 90 days of ownership are widely accepted as authoritative and unbiased; that's why car manufacturers tout high rankings in their ads. But what about the rest of the survey--if there are winners, there must be losers, right? Well, Power strives to keep the full findings confidential, partly out of consideration for client manufacturers who score poorly. Despite Power's efforts, though, pieces of the latest report have fallen into FORTUNE's hands.

First, the winners for the 1998 model year: Despite the widely held belief that foreign automakers run the soundest plants, the best-performing plant belongs to Ford--specifically, the St. Thomas, Ontario, facility where the sedate Crown Victoria and Mercury Marquis sedans are assembled. Such old-tech cars tend to have fewer problems. In fact, Ford plants occupied the top three spots in the survey, while General Motors' Cadillac plant in Hamtramck, Mich., came in fourth. Fifth place went to Honda's plant in Marysville, Ohio, while Toyota's Georgetown, Ky., complex wound up sixth. Among European manufacturers, BMW finished a surprisingly strong eighth with its Spartanburg, S.C., facility, while the best that Chrysler could manage was 17th, for the Ontario plant where it makes its big Chrysler and Dodge sedans.

Some well-known plants didn't fare as well as their press clippings might indicate. Saturn's facility in Spring Hill, Tenn., which often stars in the car's TV commercials, ranked 22nd, while Nissan's Smyrna, Tenn., plant, recently lauded as the most productive in the U.S., rated 30th. The distinction of producing the worst-quality vehicles in the U.S. fell to the Lafayette, Ind., plant where Isuzu makes the Rodeo and the Amigo sport-utility vehicles, as well as the Honda Passport.

For consumers, the Power survey contains some warning flags. Sport utilities may be hot sellers, but they have up to 50% more problems than most passenger cars, largely because they are based on pickup trucks, which just aren't as customer-friendly. The biggest complaints regarded wind noise, poor straight-line driving stability, and noisy brakes. And the old axiom about not buying a new vehicle during its first year of production remains true today. The popular Mercedes M-Class, which is built at a new plant in Alabama, has more problems than any other luxury sports utility. Not all the defects are of Mercedes' making, however. A balky remote keyless entry system supplied by an outside manufacturer produced an outsized number of customer complaints. A Mercedes spokesman says the company is working to correct problems at the plant as well as when the vehicles are in customers' hands. As for that troublesome key fob, a microprocessor chip change is under way.

--Alex Taylor III