It's not always the car as a whole that was a pile, sometimes it was just the engine. The 8-6-4 is the most notorious example even though it was one year only. Most of the crappy engines were from attempts to squeeze better fuel economy out of really large cars. One of the engines I loath the most is Cadillac's 4100 series V8. This engine was used on most Cadillac models beginning in 1982 after the failure of the 8-6-4. It had 125hp at 4200 rpm and 190ft/lb of torque at 2,000rpm. Put this in a 4,000lb. Cadillac and calling the performance "underwhelming" would be polite. The engine had to work so hard to move the car that there were no net gains in fuel economy unless all driving was done at a 60mph cruise. The intake manifold gaskets gave out fairly early in the engine's life and GM's initial response was to put "Stop Leak" into the cooling system. If there was a coolant loss and the engine overheated it was basically a goner as parts of the aluminum block would warp enough to ruin the engine. They never did get the issues of this engine fixed and it was replaced by a redesigned version that was 4.5 litres.
The 4100 is basically a deal breaker for me in my search for an old E-body or Seville. Since my target year is 1985, I would actually even take a car with an Olds 350 diesel over a 4100 because by 1985 they had the issues with the diesel worked out. The 4100 really ruins an otherwise good car.