Ok l read your problem as you said with out taking pressure reading it is a guessing game but with that said you said you replaced the pump that pump is splines it goes into the side of the timing cover on the other side is a spline gear some times the gear wears on the spline of the pump and the pump will not catch to turn take the pump back out and look real close inside to make sure the gear in the engine is in good shape and not worn out were the splines are. If that is the case. the pump wont turn you would have to take the front of the engine down to replace the gear and the chain hope l was of help.