My 496 sets an alarm for exhaust manifold over temp when idling for several minutes after I put the boat in the water. I can rev it a few times and the alarm goes away and it is fine for the rest of the day. I replaced the impeller several years ago. When looking at the freeze frame data on the scan tool it shows .6 psi for the water pressure when the code was set for the manifold temp but it does not throw a code for low pressure. I removed the belt and the pump turns with even resistance. Any ideas? I have a new impeller that I can install but it is a total pain to get to in my Baja.

Is the pump housing grooved on the sides of the impeller?

It was fine last time I changed it. I think I am going to go ahead and pull the pump and check it. It is just a total pain in the arse on this boat. No room and fuel pumps in the way.