Merc 496, Where is the IAC muffler? having strange noise

[nanzpac]

Last weekend my 496 Mag developed a strange intermitant hissing noise almost like a belt slipping sound or air intake leak. It happens every 3-5 seconds only at high speeds over 40mph. I think some of it may be due to my hatch is lifting (Ultra 21" Stealth) and the air at high speedos is hitting the air intake and making the engine suck more air.It surges the power a little too when the noise happens.

My mech said change the IAC muffler as those get dirty or even fall off. Anyone know much about changing this? If I take the arrestor screen off the intake, is it in the there somewhere. Easy fix I hear and cheap but I don't even know how to change it.

Any advice is so appreciated
Thanks

 

[Don S]

Re: Merc 496, Where is the IAC muffler? having strange noise

Do you have a serial number for your engine?

 

[nanzpac]

Re: Merc 496, Where is the IAC muffler? having strange noise

The boat is in Lake havasu but I can get it. I think I have paperwork on it at home. I can tell you that it is a 2005 boat so the motor is probably in the 2004 year or 2005. Its a stock 496 MAG 375hp 8.1L with a Bravo 1. It has the PCM555.
Thanks

 

[nanzpac]

Re: Merc 496, Where is the IAC muffler? having strange noise

Anyone?

I heard they make a K&N air filter for this that helps solve this.

 

[Fun Times]

Re: Merc 496, Where is the IAC muffler? having strange noise

Anyone?

I heard they make a K&N air filter for this that helps solve this.

If your engine needs one, Then it will be number 5 in this link.
http://www.mercruiserparts.com/Show...desc=Throttle+Body,+Mechanical+Throttle-Shift

The muffler goes under the flame arrestor, And just sits in a hole on the throttle body.

They do make a K&N filter for this engine, Not sure if it helps with keeping the IAC muffler in place, it does look nice, But it will not give you any extra performance at all like some claim, Trust me I have tested it a few times while on the lake at WOT, And nothing changed at all performance wise, Even though i Knew it wouldn't change anything, I still had to try.:redface:

This first link will work on your engine.
http://www.knfilters.com/search/product.aspx?Prod=59-5005
http://www.knfilters.com/marine/boats.htm

 

[Mike250]

Re: Merc 496, Where is the IAC muffler? having strange noise

I have the same motor/year and had the same problem without the surging. It whistled at certain throttle settings.

Once the air intake grill is off bend down and look deep into the throttle body and you'll see it or where it used to be. Changing mine didn't solve the problem but it did help.

 

[nanzpac]

Re: Merc 496, Where is the IAC muffler? having strange noise

Thanks guys. I appreciate the info. That diagram helps allot. I will buy a new stock filter since they are cheap and replace it. I will also refasten the straps for my hatch so it doesn't come up. I'll let you know.
Thanks

 

[Fun Times]

Re: Merc 496, Where is the IAC muffler? having strange noise

I have the same motor/year and had the same problem without the surging. It whistled at certain throttle settings.

Changing mine didn't solve the problem but it did help.

Mercruiser has a new style throttle body out to eliminate that loud whistling sound effect you hear at cruising speeds.

Everybody that has switched to the new style throttle body loves it, Especially you cobalt owners with the 250's.

 

[Mike250]

Re: Merc 496, Where is the IAC muffler? having strange noise

Usually the whistling sound comes from women on shore.

 

[nanzpac]

Re: Merc 496, Where is the IAC muffler? having strange noise

Usually the whistling sound comes from women on shore.

They stopped whistling at me now that I have 2 youngens and a Mrs on board, but yes thanks for the props.

 

[nanzpac]

Re: Merc 496, Where is the IAC muffler? having strange noise

Mercruiser has a new style throttle body out to eliminate that loud whistling sound effect you hear at cruising speeds.

Everybody that has switched to the new style throttle body loves it, Especially you cobalt owners with the 250's.

Is this a free lifetime warranty item or something you buy for $1200?