UNSANE

I had the same thing happen to my 350 Mag in my old boat. Take off the flame arrestor top and see if there's a little dime sized piece of foam hanging out down there. There is a place for that to go somewhere inside of there and I was told they can pop out pretty easy sometimes.

JasonSmith

I see your point, but rember there are people who will spend $100k on an engine that whistles. I guess it all is in your perspective.
I think I'd contact Mercruiser & ask them directly if there is a fix.

BryanTuvell

I have Two 2003 496 HO's in my 33ZX DONZI, they have just 200 hours on them, and they are as quiet as a church mouse...
I will be listening closely soon though.

Great data thread, Thanks.
Bryan

speedreeder

First thing is you need to find out if your motor has set a code in the computer. If not then look in the throttle body for this piece of foam(it is called a filter by Mercury). Believe it or not there is a small hole in it that runs through the center, It has to be lined up straight up and down. I have had this on another boat that the temp. sensor for the coolant was telling the computer it was colder than what it really was. It is not the temp. for the dash gauge, But for the computer.

Kboo

speedreeder, what is the simplest way to read codes I see a co called rinda.com sells readers any suggestions

Raylar

The whistling you can sometimes hear on 496's is coming from the throttle body opening that feeds air into the hose that runs back to the idle air controller that Mercury mounts on the back of the stock intake manifold. On most 496's Mercury puts a small piece of foam in this opening to lessen the whistling noise. This noise is caused when backing off or having the motor at low approx. 1500 rpms when the idle air motor opens for a short time wide open to keep the motor from stalling when commanded to do so by the ECM. Once the idle air stabilizes the idle or rpms it closes down to a smaller orfice and the whistling stops or gets noticably less. If your motor has an excessive whistle from this opening, check your TPS voltage at idle with a scan tool. It should read between about .49volts to .63 volts. If its outside this range it could indicate aproblem with your TPS sensor. Oh, TPS is throttle position sensor for those who might not know this term.

There are obviously other whistles and squeals that eminate from 496's, but this is generally the one most 496 owners hear and question. the good news is that its harmless and generally not to noticble over the roar and rumble of a Raylar equipped 496!!

Regards, Ray @ Raylar

Dave_N

Ray,
I'm unclear as to how the TPS voltage will cause the IAC valve to operate improperly. Isn't it more important to check for normal IAC position/activity?

I'm more inclined to think that an (overly) open IAC is indicating an IAC problem (if the idle speed is high) or engine performance issue (if the idle speed is normal).

Dave

Raylar

Dave:

Thanks for your question. When we have seen whistling from the IAC we have sometimes found the voltage on the TPS circut out of range. Usually its a TPS problem on the voltage range but you are right that sometimes the IAC motor can be bad and sometimes they stick and can cause the same increase in feed air or response and the whistling will be more pronounced. The IAC counts or activity to high can also signal a problem IAC, but it usually shows itself with stalling or rough idle. Just our findings, what are yours?

Regards,
Ray @ Raylar

betitbig

Do you know how much money I spent to get my 496 to whistle...

Dave_N

Ray,
Thanks for the response. I won't pretend to know anywhere near what you know about the 496, and I appreciate you taking the time to enlighten me.

My findings on the 496 are:
1) Most of the time an IAC failure will set a fault code/soft alarm
2) The typical IAC activity of a 496 is different from other engines, even those that use the same PWM IAC valve.
3) A "whistling" IAC is usually a symptom of another problem.

Dave