Whistling noise-350 MAG MPI.

[DaleM]

The engine on my 270 has a whistling noise when running between 2800 and 4000 rpm.  I can't seem to pin it down.  It's most noticable at about 3400.  It does change in pitch over that rpm range not necessarily louder or higher with increased rpms.  Because of the change in pitch not being consistent with rpms I have ruled out most mechanical items such as belt, alternator, water pump. etc.  Any ideas?

[cwzonk]

Dale, I have the same thing on mine.  really notice when I have the camper sleeper up.  Had a mechanic out with me and couldn't find any problems, good belt...  he said not a mechanical issue.

[DaleM]

That kind of puts my mind at ease.  Guess I'll need to put an amp in for the stereo.  That should do it.  Speaking of that, how are your speakers wired?  I didn't really play with the balance too much but it seemed as though the 2 middle speakers located by the pilot seat and right across the cockpit were't working the other night.

Also posted this at http://www.crowniehq.net to see if anyone over there is experiencing the same thing with their 350 MAG MPI engines.

[DaleM]

Okay so far I've been told it's the air flow through the air filter causing the noise/whistling.  Still don't know what can be done about it.

[cwzonk]

I never played with the ballance but my port back speacker is cracked and wired wrong going up to the one by the arch and it cuts in and out.  I have good sound in both until you turn up the volume so I disconected the back and deal with the one in front of it.  My youngest boy is coming home from the army for a month and he is good at that kind of thing.  

Hopefully we can get to the boat by then.  They just shut the river down until further notice

[DaleM]

Apparently this whistling noise we are hearing isn't anything new.  It's definitely caused by air flowing through the flame arrestor.  Some of the guys at the other site I visit have replaced their arrestor with K&N filters.  Thing is you have to measure the intake throat opening and then locate one that fits.  I'm going to run the boat with that arrestor off some time this week.  I'll let you know what happens.

Also starting goofing with the radio.  Some components located above the microwave.  The CD player down in the front port storage.  Anyway I had it playing and decided to unplug the amp that's up there.  Nothing happened.  Plugged the amp back in and checked it's fuse, it's good.  I'm going to have to track this wiring down.  I only have 4 of the 6 speakers working.  Balance and fade are working correctly.  Just get nothing to the middle 2 speakers.  Nor does it seem like that amp is doing anything.  Think I'll start a thread for this stereo thingy.

Too bad about the river.  I also heard they closed the Chain of Lakes down up here as well.  Water is just too high to boat.

UPDATE:  There are alot of guys with this same engine that never hear the whistling noise but that's because they have Corsa exhaust systems.  WAY LOUD!!!!

[Mikes342]

On the 350 mag in the carb their is a small item that looks like a small piece of cotton.  I had the same thing happen and put a new one in and it quit hissing.  Look up the parts for the 350 Mag mpi engine parts and you will see the part.  I think they called it a muffler.  Not a joke.  Your merc mechanic should know what it is.

If yu take off the flame arrestor you will be able to see it if it is  there.  If you know someone who has the same engine take give them a beverage and ask them if you can take their flame arrestor off and you will see it. It appears to be a white piece of cotton.

Let me know if you need more information and I will look up the part.

Mikes 342

[DaleM]

Mike I find that muffler on some of the drawings I have located but fail to find that part on the drawing for my specific engine.  Any chance you could get me a part number?  My engine is a 2000 350 MAG MPI S/N # OL629609.  Thanks for your help.

[cwzonk]

Dale, I would look at mine but my marina is 6' under water... I have that manual also; but, on the boat.  Maybe by the 4th I can take my other boat to my rinker.  Only if they open ther river back up to rec. traffic.  Let me know if you find anything out about this noise.

[DaleM]

Messing around with mine today.  Adding that 12v plug in for the ipod and putting blue leds under theb swimplatform.  Soon as I get those things done I'll look into the carb muffler thingy.  Someone else over at CrownieHQ mentioned something about that also.

[Dream 'Inn]

I have the whistling noise on only one of my two engines and it only happens at the lower end RPMs.  It was there when I bought the boat, and the surveyor I had said it was thru the air filter and not an issue, he sees it all the time.

[DaleM]

Got out yesterday for about 4 hours.  Great time.  Pulled the spark arrestor and took some pictures.  I'm thinking that little square hole in the photo is the only place I could see fitting that muffler thingy into.

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[DaleM]

Another update:
Talked to Merc about this today.  They told me to take it to my dealer.  Told him how some of you had taken yours to a dealer with nothing wrong with the engine and a service bill to show for it.  He told me to run 89 octane fuel.  Then proceeded to tell me that there is information about that engine that he cannot give me because I am not a factory authorized dealer.  Now that's just B.S. !!!  Not sweating it boat ran great this weekend.  Just going to have to live with it for now.

[Mikes342]

Dale,

I have been looking for the parts breakdown that I found it in.  I am having trouble finding the information.  It will not hurt anything to run without it in.  I ran it all summer long without any problems before I traded my 270 in for my 342.   It just hisses.  I will keep looking into my archives and I am sure I will come upon it again.

If anyone with a 350 mag can take a picture I am sure it will help Dale out.  We all now how frustrating it can be to have anything wrong with our boats.

Mikes 342

[DaleM]

Got some recommendations from the guys over on http://www.boatus.com message boards.  Told me to clean out the throttle body and remove the IAC and clean it as well.  Clymer manual has a pretty good break down of how to do it so I will give it a whack next weekend.