I have a 1990 454 magnum with factory silent choice exhaust with the compressor and air cylinders for opening and closing the exhaust. The problem is when the cylinders pump up and open the exhaust, the system loses air pressure and the diverters close. I tried soapy water on connections which showed no leaks. How could I pump up the cylinders to see if they are leaking? Or does anyone know of any problems that would cause the problem on this system.

I got sick of fooling around with mine......all the connections, pump, cylinders etc.....sometimes work sometimes not.....faaaack......switched to Corsa electric......ez wire up....DONE!!......that was 3 yrs ago both sets still work perfect.......bought them used off an OSO member......do it.

alot of times the solenoid valve that locks holding the air in the cylynders i faulty and wont hold pressure.you can test individually by removing first tee in the pressure line and installing each pneumatic cylynder one at a time to see if htere faulty. then change bad one. if not you just add hose until system doesnt work then change bad fitting, ferule or segment of line.

I second monstaaa's thought.
Mine had a dirty relief valve. Wouldn't seal 100% and slowly leaked down. Item #11. It's nothing more than a spring loaded seal. A little dirt, and she leaks. I just removed and cleaned it real well and never had another problem.

http://www.mercruiserparts.com/Show_...+Pump+Assembly

Thanks, I'll try that first. Thanks for the picture diagram. Part number 11. I'll let you know how I make out.

I cleaned the relief valve out and that seemed to work but the starboard side cylinder wasn't opening exhaust all the way so I took the pin off the what I assume is the flapper in the wye connection and the cylinder would pull all the way back but just trying to move the arm on the flapper by hand was really tight. Didn't move very easy. Any ideas?

you should be able to remove the bolts that hold the flapper to the shaft, thru the tail pipe. then remove the shaft and clean the corrosion. saturating the whole unit inside and out and letting it sit will help to loosen the bolts, because they do snap. clean it up lube it, reasssemble.

I wish I could do that but not sure how much of a problem it is to get the back wash flappers out of my tips in order to get to the divert flapper. I also put a pressure gauge on the discharge of the compressor and when I activate it, it goes up to 30psi and then starts to drift down right away. Starting there and moving forward. I still will have to work on making the starboard divert move more freely.

thanks to monstaaa and us fountain my silent choice is fixed. It was the relief valve. Took it all apart and cleaned the seat and seal pumped it up and it holds for hours at 32psi. Will test on the water saturday. Thanks

Good deal.