What is this noise?

[minnmarker]

Installed new intake plenum gasket. No change. Stumped.

Ideas anyone???

[TenTwentyOne]

So, the noise goes away when you throttle up? It is an odd noise. That said, with everything else you have eliminated, I would definitely guess that it has a vacuum leak. Does it only make the noise at idle?

I know how I check for those in a car........ But not sure I would be comfortable doing it in a boat..... (Spray carb cleaner in suspected areas and listen for a change in RPM) 

 

[airshark360]

Looks like I'm late to the party but it really sounds like a fuel pump whine to me. 

[minnmarker]

4 hours ago, TenTwentyOne said:

So, the noise goes away when you throttle up? It is an odd noise. That said, with everything else you have eliminated, I would definitely guess that it has a vacuum leak. Does it only make the noise at idle?

I know how I check for those in a car........ But not sure I would be comfortable doing it in a boat..... (Spray carb cleaner in suspected areas and listen for a change in RPM) 

 

It is a high pitched whine.  On a cold start it takes anywhere from 10 seconds to a minute to start after the engine starts.  On a hot or warm start it is there right away.  It is loudest at idle.  When I use the neutral lockout it momentarily goes away when I blip the throttle but then comes back right away.  I have not tried revving the engine beyond 3,000 rpm in neutral.  It is present at idle whether in gear or not.  It seems to go away at about 3,000 rpm in gear.  That and the blip effect makes me think vacuum leak - but where??  Butterfly valve and throttle body gaskets are on the other end of the engine.

It is definitely on the front (belt side) of the engine.  I have replaced the intake plenum gasket and checked the only 2 hoses (both @ 3/8") I could find - one that goes from he valve cover to the air intake and one that goes from the other valve cover to ???  Unplugging or pinching these hoses had no effect.  There is no PCV valve, just an open hose.  No detectable blow by coming out of the valve cover holes.

Engine operation seems totally normal.  There are no oil leaks from the engine or water leaks from the engine or raw water system.

I tried pointing an unlit propane torch around the intake plenum above the fuel rails and did not detect any change in rpm - but I did it fast and was scared as heck and will not do that again.  May try the carb cleaner technique unless someone has a better idea.  Where should I spray?

[Bill_AirJunky]

On my Monsoon, I'll get something that sounds like this when the Perfect pass servo rotates around the hose it's mounted on till its resting against the big aluminum pulley.  I just rotate it back off the pulley & secure it.

Sounds too loud to be the fuel pump, not to mention wrong end of the motor. But when I had it, I replaced the fuel filter and all was well again. 

Edited August 15, 2016 by Bill_AirJunky

[minnmarker]

Just now, Bill_AirJunky said:

On my Monsoon, I'll get something that sounds like this when the Perfect pass servo rotates around the hose it's mounted on till its resting against the big aluminum pulley.  I just rotate it back off the pulley & secure it.

Thanks Bill - but it makes the noise even with the PP servo completely unplugged.  The PP servo is in the same neighborhood as the sound though.

[Bill_AirJunky]

Just now, minnmarker said:

Thanks Bill - but it makes the noise even with the PP servo completely unplugged.  The PP servo is in the same neighborhood as the sound though.

Unplugged and removed?

Make sure there is nothing dragging on that pulley as it spins.

[Woodski]

@minnmarker:  Sounds like a high RPM pump noise, fuel pump certainly comes to mind.  I can envision that it also sounds like air sucking through a small passage creating the whistle, intake manifold or any seal in a high vacuum area particularly since it disappears when vacuum level drops.  Besides propane, you could shoot some starting fluid (alcohol) at those particular seams/joints to see if RPM is affected.  I might also grab and hold any fuel pump to see if that changes the pitch.  Too high a frequency for a raw water pump IMO.

There is a thread on this site of a high pitch noise coming from the intake manifold and a fix to correct it, do a search for it.  Has to do with the configuration of the parts and a solution that alters the air flow path to stop the noise IIRC. 

Thread:  "High Pitch intake whistle GONE!"

 

Edited August 15, 2016 by Woodski

[minnmarker]

7 minutes ago, Woodski said:

@minnmarker:  Sounds like a high RPM pump noise, fuel pump certainly comes to mind.  I can envision that it also sounds like air sucking through a small passage creating the whistle, intake manifold or any seal in a high vacuum area particularly since it disappears when vacuum level drops.  Besides propane, you could shoot some starting fluid (alcohol) at those particular seams/joints to see if RPM is affected.  I might also grab and hold any fuel pump to see if that changes the pitch.  Too high a frequency for a raw water pump IMO.

There is a thread on this site of a high pitch noise coming from the intake manifold and a fix to correct it, do a search for it.  Has to do with the configuration of the parts and a solution that alters the air flow path to stop the noise IIRC. 

Thread:  "High Pitch intake whistle GONE!"

 

Yep.  I posted in that thread and did get rid of the dreaded butterfly valve whistle by rounding off the corners of the disk. While that was annoying last year, the new whine is much louder.  It is not the fuel pump.  That corner of the engine is purring along nicely.  The whine is coming from the engine water pump area or raw water pump area or aft part of the intake plenum area or crankshaft pulley area.  As mentioned earlier in this thread I took the belt off and it was still there so not the alternator or the engine water pump.

[minnmarker]

I'm thinking/fearing that it is a leak in the intake manifold gasket - either upper or lower - but I'm not getting any misfires or other engine problems so perhaps it is very small.  Will try the carb cleaner diagnostic but will take it to a real mechanic before I start pulling manifolds off...

[minnmarker]

On 08/15/2016 at 7:02 AM, TenTwentyOne said:

(Spray carb cleaner in suspected areas and listen for a change in RPM) 

 

TenTwentyOne, found it with carb cleaner! Thanks! Unfortunately it is the intake manifold gasket. Leak must be isolated to the outer edge on left front of engine. Will try tightening and torquing the bolts tomorrow. Hope I don't have to replace it. No water in oil or oil leaking or smoke or steam in exhaust so I think its just an air leak. No apparent impact on engine performance at idle or under load so maybe it's very a very small leak.

[Roush611]

You sound pretty mechanically inclined. I would be willing to bet you can replace the intake manifold gasket yourself if you have the time. I did the one on my Tahoe and it was not all that bad. Just took a bit of time. 

[minnmarker]

It was the intake manifold gasket! 4 hour job on the boat lift. Quicker, easier, and cheaper than taking it 2 hours to the dealer and waiting more than a week to get it back and then 2 hours bringing it back. Thanks @TenTwentyOne and @Shastasurf for the help.

You can see dark areas where the leaks were on the bottom gasket in the picture. I think whoever installed the manifold screwed up the placement and/or the torquing. The bolts on the side with the leak were very loose and the ones on the other side may have been too tight. Fortunately there did not appear to be any water leaking out of the water passages.

So no high pitched whistle anymore! This has been a too long diagnosis.

Edited August 30, 2016 by minnmarker
Link addition

[echie]

54 minutes ago, minnmarker said:

It was the intake manifold gasket! 4 hour job on the boat lift. Quicker, easier, and cheaper than taking it 2 hours to the dealer and waiting more than a week to get it back and then 2 hours bringing it back. Thanks @TenTwentyOne and @shastasurf for the help.

You can see dark areas where the leaks were on the bottom gasket in the picture. I think whoever installed the manifold screwed up the placement and/or the torquing. The bolts on the side with the leak were very loose and the ones on the other side may have been too tight. Fortunately there did not appear to be any water leaking out of the water passages.

So no high pitched whistle anymore! This has been a too long diagnosis.

Now I know what to look for if I ever exoeriance a high pitched whistling!!!     Lol. ...

I knew that was an odd one when I first heard it!!  Not everyday that happens!!!

Lol

Glad u got it figured out!!!

[TenTwentyOne]

Awesome! Glad you finally got it figured out!

[Woodski]

Just a note to any future intake manifold gasket swaps, common trick is to spike or use a punch and make several punch marks on both the cylinder head and the intake manifold to create a better grip surface.

[Shastasurf]

34 minutes ago, Woodski said:

Just a note to any future intake manifold gasket swaps, common trick is to spike or use a punch and make several punch marks on both the cylinder head and the intake manifold to create a better grip surface.

Just where u are applying the rtv?

[Woodski]

The narrow section of the gaskets along the vertical walls of the siamesed ports are the prime area for a gasket slip or failure.  By creating a pickled or rough surface, you create a better change for the gasket to grip and not move over time and use.  Most intake manifold gaskets come with a rubberized sealing ring already on the gasket.  Main area of adding some RTV would be on the gaps at the front and rear for the intake to block and corner of cylinder head where the cork and main intake manifold gasket join.  Several Chevy or small block sites should have video demo's.