7: Isuzu I-Series
You might not be familiar with the I-Series brand, and that’s because Isuzu left the American car market shortly after the release. The more familiar versions of the I-Series were the Chevrolet Colorado and the GMC Canyon twins. These trucks were notoriously unreliable for many reasons, but the main one came down to the five-cylinder engine (via Auto Trader).
There was a defect in the heads that caused the engine to malfunction at low mileage. This failure would cause an engine misfire that could never be diagnosed or fixed. GM never provided any support for this, so owners were forced to eat it. That wasn’t a sound business, and the Colorado brand never recovered from this mishap.