The copper-cooled engine: In the early 1920s, looking to eliminate the cumbersome radiator and reduce engine parts, chief GM researcher 'Boss' Kettering championed the 'copper-cooled' engine. It was an air-cooled engine using copper fins and a fan rather than a radiator. Despite several design changes, there were technical problems. The engine pre-ignited badly when driving at moderate speeds in 60- to 70-degree weather. When hot, it lost compression and power. The program was put on hold, and Chevy built fewer than 800 vehicles with the engine. Chevrolet Corvair: Many people credit the Corvair with sparking the federal government's vast push into automobile regulation. In his book 'Unsafe at Any Speed,' Ralph Nader noted that the Corvair's single-piece steering column could impale a driver in a front collision. The Corvair had other shortcomings, too. 1971 Chevrolet Vega: The latest in a string of small cars from GM, the 1971 Chevrolet Vega was plagued with quality and cost problems from the outset. The four-cylinder engine suffered from material woes, including an iron head. And it never met GM's internal sales targets. 1980 Chevrolet Citation, X-body cars: With a 2.8-liter V-6 engine and front-wheel drive, the futuristic 'X-body cars' were GM's boldest attempt to take on the Japanese. Chevy moved 800,000 Citations in 1980, but demand led to problems. Faulty brakes and steering problems sparked recalls and hurt sales. 1981 Cadillac Fleetwood V-8-6-4: The V-8-6-4 program, the first attempt to idle unneeded cylinders to save energy, became the Titanic of all engine programs -- as Time magazine put it. The big cars often shook, stalled, made crude noises and misbehaved until owners hauled them to have the system disabled. 1982 Cadillac Cimarron: GM priced the new compact Caddy -- with an unconventional I4 engine and four-speed manual transmission -- thousands of dollars more than the similar Chevy Cavalier. It became the unwanted poster child of bad badge engineering, insulted Cadillac fans and nearly doomed the division. Olds 350 diesel: In the late 1970s and early 1980s, responding to fuel economy concerns, GM's divisions embraced V-6 and V-8 diesel engines with disastrous and costly results. The engines were dogged by poor design, bad diesel fuel and improper service and maintenance. More than 1 million were sold between 1978 and 1985, but their high failure rate tarnished diesels for decades. Under a settlement with the federal government, owners were able to recover 80 percent of the cost of failed engines. 1988 Buick Reatta/1987 Cadillac Allante: The hand-built Reatta's 'excessive' level of electronics was a turn-off to some older, core buyers. The Allante featured a body designed and built in Italy and shipped to Michigan on Boeing 747s, but it was too high-priced. Pontiac Aztek: At its debut in 1999, the Aztek crossover drew raves for its sporty styling and versatile features. But the production version fell victim to bureaucratic product development and a zealous finance staff intent on cutting costs. And it was priced out of reach of its targeted 'Gen X' buyer. David Phillips