depends which FTL you're talking about. Hyperlanes VS hyperlanes, it's almost 100% impossible to catch them if they don't want to be. I've auto-chased a fleet halfway across the galaxy being literally about 0.2 seconds behind him, but they're programmed to run away indefinitely.
It's not their fault that your warp tech sucks. If you have a better drive than they do, you'll catch 'em and crush 'em.