I recently had a the engine replaced on my 1991 Acura Coupe. When I got it back from the shop I heard knocking upon acceleration. At first, the check engine light was on, but the code indicated it was the EGR valve. When I replaced the EGR valve the light went off, but the knocking persists. I had the timing checked it is 13 on 15 degrees -+ 2. The vehicle has two knock sensors and one fuel injector pressure regulator. What do you think is causing the knocking and is it damaging anything?