350MAG making hissing noise

[billyman]

I noticed yesterday my engine started making a "hissing" noise and after some inspection I think it's coming from the air intake.

Here's a video I shot. I can hear it clearly, but then again I know what my engine sounds like. Hopefully you guys can hear it and point me in the right direction. Thank you.

https://www.youtube.com/watch?v=PuP1FZ7ud8g

 

[84EdH]

Re: 350MAG making hissing noise

Billy, it is really tough to "here" noises from videos etc. That being said, it could be a vacuum leak. Culprit places are at base of intake manifold, base of carb, vacuum hoses etc. here's how to check. With the engine cold, squirt carb cleaner around these areas and listen for a change in the idle speed of the engine. A leak will suck in carb cleaner and change the idle for a few seconds. If you find a suspected spot, repeat to confirm......then fix it.

 

[Walt T]

Re: 350MAG making hissing noise

Key word in his answer is COLD engine. Also make darn sure there are no stray sparks or be prepared to borrow the wife's eyebrow pencil

 

[Hoosmatroos]

Re: 350MAG making hissing noise

I think it's the IAC (Intake Air Control) Muffler in the throttle body, the part no is 35-863829 cost you around $2, will fix your problem. Easy fix, you can do it yourself.

 

[Fun Times]

Re: 350MAG making hissing noise

I think it's the IAC (Intake Air Control) Muffler in the throttle body, the part no is 35-863829 cost you around $2, will fix your problem. Easy fix, you can do it yourself.

Most likely.

 

[Hoosmatroos]

Re: 350MAG making hissing noise

http://www.mercruiserparts.com/Show...691.png&inbr=7752&bnbr=80&bdesc=Throttle+Body

Part number 6 is the one to replace. Probably the old isn't there anymore.

 

[tpenfield]

Re: 350MAG making hissing noise

Not sure about the IAC . . . could be. . . but from the video, it also sounds like bearing noise :noidea:

As stated, it is fairly tough to tell from a video. You could listen through a tube to isolate the noise a bit better.

 

[billyman]

Re: 350MAG making hissing noise

The foreign sound really sounds like it's coming from the air intake so my next step is to look for the IAC muffler, but thank you all for the suggestions. I'll report back w/ my findings.

 

[billyman]

Re: 350MAG making hissing noise

I hope I'm not making a mistake reviving a 7 month old thread, but I wanted to confirm to all that suggested the AIC muffler (filter) was the issue, you were correct. $1.50 and the "hissing" noise is gone. It sure is nice when something is a cheap and simple fix.

Thank you and I hope this serves someone else in the future.

 

[Scott Danforth]

Re: 350MAG making hissing noise

its your thread, you as the OP can revive it any time you want