DETROIT — Pontiac, the brand that invented the muscle car under its flamboyant engineer John Z. DeLorean, helped Burt Reynolds elude Sheriff Justice in “Smokey and the Bandit” and taught baby boomers to salivate over horsepower, but produced mostly forgettable cars for their children, will endure a lonely death on Sunday after about 40 million in sales. It was 84 years old. The cause of death was in dispute. Fans said Pontiac’s wounds were self-inflicted, while General Motors blamed a terminal illness contracted during last year’s bankruptcy. Pontiac built its last car nearly a year ago, but the official end...