2005 175 optimax water pressure alarm

[Basketcase]

Hey guys. I've got a motor on a boat I recently purchased that has a very intermittent alarm. When it happens, it happens at high rpms, mostly around 5k and stops immediately when I reduce throttle, even just a little. It used to happen a bit sooner before I replaced the water pump. (complete OEM unit). I figure I'll do the basics first that I can justify as maintenance items. Clean the strainer, replace thermostats and poppet valve. When I opened up the poppet valve, there was some grass under the diaphragm between its plate (the one that moves with the diaphragm) and the plate that the whole assembly mounts to, visible after removing the screw. I've run the motor in clean water, and flushed it so it wasn't coming out through normal use. Could this cause a problem like this? I want to say yes, but thinking about how the system works, I'm skeptical. I havent opened up the starboard thermo yet, but the port side was not obstructed. There was a slight amount of grass in the strainer leading to the air pump. The grass in both cases is thick sea grass as this is a motor used exclusively in salt. Even so, I'm finding no corrosion inside any of the passages I look into. I cant say the same for my Etec on another boat.

I also notice my plugs are black, which would indicate running rich, which may mean running cold? Might indicate stuck open thermostat or that obstruction in the poppet valve?

As for replacing the thermostats. Port side was easy with just the 2 bolts, but starboard is blocked by the air line fitting. I see most things online say to loosen the fuel rail and slide it off a little but it looks like if I just remove the allen that holds the retainer plate for that air line, it will come out and I can access that bolt? Is there a good reason not to do it that way as long as I plug the holes so debris doesn't get in?

Given this info, what advice can you give? It is much appreciated. I'm not a pro mechanic, but better than average with a wrench. Just need some guidance.

[JOE54]

ser num and v6 section one down ,you can remove fitting ,need temp monitor and wpsi at wot

[Basketcase]

Serial #1B119293. I thought this was the right section because its a stock motor. I thought the one below was for "high performance". If I'm in the wrong spot, can a moderator move it? (should have read the sticky)

Currently I do not have gauges for temp and PSI but I'm going to do a smartcraft tach so I have all that.

Thanks for the info about the fitting. Seems a lot easier than removing the fuel rail.

[JOE54]

[Basketcase]

Would you think that a little grass stuck in that spot could be enough to hold the poppet open just a tad and make it not build enough pressure?

[JOE54]

yes it could

[SilverFox579]

Serial #1B119293. I thought this was the right section because its a stock motor. I thought the one below was for "high performance". If I'm in the wrong spot, can a moderator move it? (should have read the sticky)

Currently I do not have gauges for temp and PSI but I'm going to do a smartcraft tach so I have all that.

Thanks for the info about the fitting. Seems a lot easier than removing the fuel rail.

Title for that forum is missing the "&" between displacements and high performance - it is correct place for questions about your 2.5L Optimax (caught me too when I first joined BBC).