I Heard there were alot of things that went wrong with a 4.0 v8 engine?
What years did that occur? Is there anything you should look for when buying one of these years? Is there anything you should do to keep them running their best?

 

The 4.0L engines, introduced in '97 (US) came with a number of issues slowly resolved over a number of years.

The original AJ26 ('96 - '98) came with:
a water pump that failed within a couple years
a plastic cam chain tensioners that failed within a couple years
a nikasil lining to the cylinder that failed within a couple years if subjected
to high sulfur fuel

The later AJ27 engines ('99 - '02) still had the the Nikasil cylinder lining until Aug -'00 and the plastic tensioners until after Sept (Aug) '01.

Other than that they are perfectly wonderful engines.