V8-6-4

I just bought an 81 eldorado with the v8-6-4 engine. It only has 70 K orginal miles and in great shape. Currently the 8-6-4 is working when it should but I am finding a bunch of bad reports on it. What exactly does this engine do that is so bad(that I haven't experienced yet)? I really don't like the system and wish it would just stay in 8 cycs. Not only that but it gets terrible milage as it is. On the freeway it gets 21 and 11 in the city. Is this something that I should get rid of quick while it works?