1999 7.4L Whistling Noise

[Cobalt226]

I just bought a 1999 Cobalt 226 with a 7.4L Mercruiser. The engine only has 156 hours and runs great but makes a very annoying whistling noise when backing off throttle around 30 - 40 MPH. I have been told that this is from the throttle control valve and I have installed a IAC filter that I was told would solve this issue. It helped but did not eliminate the noise. I have consulted my Cobalt dealer and Mercruiser support and I am being told nothing can be done. Someone out there must have same problem and has come up with some way of fixing this!? This boat is so beautiful and runs so great that I am going to be upset if we have to live with this noise. Is there anyone out there who can help? Thanks!

 

[ni7irs]

Re: 1999 7.4L Whistling Noise

I had the same problem with mine and installed a K&N filter. It helped but did not eliminate it. I think these are just whistling engines.

 

[Cobalt226]

Re: 1999 7.4L Whistling Noise

I had the same problem with mine and installed a K&N filter. It helped but did not eliminate it. I think these are just whistling engines.

Can you tell me what a K&N filter is? The filter I installed (IAC) was a small sponge that went into the throttle control valve.

 

[ni7irs]

Re: 1999 7.4L Whistling Noise

Can you tell me what a K&N filter is? The filter I installed (IAC) was a small sponge that went into the throttle control valve.

http://www.knfilters.com/marine/boats.htm

Here is the link. You can get it from an auto parts store, I forget which chain it is, but call K&N first and get the model number from them. I tried to do it myself and I bought the wrong one.

 

[Scott Danforth]

Re: 1999 7.4L Whistling Noise

its likely the air whistling across the throttle plates.

 

[Cobalt226]

Re: 1999 7.4L Whistling Noise

its likely the air whistling across the throttle plates.

Hi Scott, that is what I have been told and I am pretty sure you are correct. But I have to be able to do something to fix this? It is really annoying and happens right in the perfect cruise range of this boat. The engine sounds so pretty until this noise happens and then it is terrible. I am sure hoping someone out there found out a way to correct.....Thanks!

 

[Scott Danforth]

Re: 1999 7.4L Whistling Noise

dont slow down, or dont go above 30mph

 

[Failproof]

Re: 1999 7.4L Whistling Noise

Install a tornado into the intake tract, change filter/flame arrester style and/or mounting distance, knife edge or round off the throttle plates. Install a intake screen, or a v-bar. Anything to change up the flow of air from what you have now will alter the whistle. Either smooth it out or disrupt it. And radius the ports on the intake for the iac, breather, and vaccum ports.