I have a 2002 kia rio cinco 1.5L engine, (97,000 miles) i have changed the timing belt and water pump 2 weeks ago, changed the spark plugs, spark plug wires, i have checked the compression in each of the cylinders and they were all equal (175 psi). However my check engine light is on and reads P0304 which states that cylinder 4 misfires. I have noticed by accident that there is a crack in the exhaust manifold right under where cylinder 4 is, and air gets out from it. Would it be the exhaust manifold that causes this or something else?? Thanks, appreciate the help.