Thru hull exhaust not working

[metolious69]

I have a '94 Baja Islander with a 350 Mercruiser. Just fired it up for the first time this season, everything runs great but the thru hull exhaust doesn't seem to be working. Water is coming out the exhaust, but the engine doesn't have the rumble that it should. I've checked to make sure the silent call switch is turned off. I've heard that it could be things from the impeller to the accuator solenoids. I'm not sure what brand the exhaust is and not sure what to check first to diagnose the problem.

Any help appreciated.