Ferguson says he expects more goals from his team in the final months.
When asked if United have still to hit top gear, despite sitting top of the league, he told Inside United: "You might be right. Where I think we can improve is that we don't seem to kill teams off.
"We've beaten Wigan 4-0 on two occasions but those are the only matches we've won by that sort of margin [ahead of the Norwich clash]. In a normal season, I'd expect a few more wins by that sort of distance. Last year, we won 5-0 against Wolves, Wigan, Bolton and Fulham, and we beat Arsenal 8-2, of course.
"We're not seeing those results this season, however. We haven't hit those heights. Hopefully, there's more to come and we'll discover that killer instinct that our teams in the past have had."