BOB is correct, the pump has to be spill/flow timed.. you might find a video on "flow timing a pump" on utube.
IF you don't do it correctly it may have terrible results..$$$$
IF you hired a mechanic or it was YOUR mechanic.. 1st thing I would do is kick him off the jobsite for not timing it BEFORE he pulled it off.. and cost you money and down time.. but hey, that's just me..
NOW IF it was a friend and he was "helping" you out.. get him back over there, crack open afew cold ones and lets figure this out..
Remove the side cover on the pump.. 2, 10mm screws.. rotate the gear on the front IN THE CORRECT ROTATION until #1 tappet begins to rise [front one] and stop.
The correct rotation is stamped on the pump nameplate IN THE PES p#.. PES6a...720 RS... OR LS... The R is for right and L is left.. LOOKING AT the front of the pump.
NOW get your engine timed.. if you cant find any videos on flow timing. mail me direct and i'll try to walk you thru it..