FIG. 1 is a perspective view of an engine cover of our design; FIG. 2 is a front view thereof; FIG. 3 is a rear view thereof; FIG. 4 is a top view thereof; FIG. 5 is a right side view thereof; and, FIG. 6 is a left side view thereof. The bottom view is not seen in ordinary use and is not part of the claimed design.