Alright, I have searched this issue and found good information pertaining to the TB whistling problem, but I do not think that is my issue. I believe the whistle is coming for somewhere else around the intake system. Here's my problem:

On a cold engine, there will be no whistle what so ever. It is only until the engine warms up a little that it spontaneously just starts to whistle very loudly. This whistling only happens at idle or very little throttle. The whistle is so loud that you can hear it from about a block away, and my car is also running straight pipes. So you kind of get the idea of how embarrassing it is to drive around with this problem.
Another thing is that once I turn the engine off, and the belts stop, the whistle will continue for about a second, they very vacuum-like, die out and raise in pitch over the next 2 seconds.
I thought it was my TB, so I took off my intake elbow and while the car was running I put my fingers around the edges of the blade, and tried closing off all the separate holes inside where air was being sucked in and none of this effected the whistle in any way (except making the car slightly die out).
I listened as best I could, but I could not locate exactly where its coming from... at times its sounds like in the front of the engine, and other times seems like its coming from the back of the engine. Its a newly rebuilt LS1 and I only have about 200 miles on it. Its been doing this ever since I got it running properly.

I just can't figure out what would cause the whistle only once at operating temperature and only when its at idle, or barely open throttle.

Please guys, any help is very much appreciated.

Any suggestions?

Thanks,
John

 

you said you took off intake elbow so im assuming you checked all connections around there like the hose clamps and such. try checking all vacuum lines

 

get a stethoscope or just a little hose and follow the sound to where it gets stronger.

 

I did check all the hoses, and the MAP sensor, and made sure my valley cover was bolted on tight, and a few other things. I'm pretty sure everything is tight.

Good idea, I will give that a try. I'm maybe just a bit hesitant about: loud whistle + stethoscope... I'll just hold put it near my ears.


Could it be possible that there is a hairline crack in the bottom of my valley cover on the inside that I wouldn't be able to see, and when it heats up it expands, causing the crack to enlarge and start to whistle?

 

that was going to be that I was going to say it might be in the intake manifold though. Did you just do a swap or something?

 

I didn't swap anything out, but its a new rebuilt engine, so all the components on it have not been used by me before until now, if thats what you meant.
It's the stock intake manifold, but I did not check it or put it on, the builders did.
Can there be a crack underneath, on the back side where its not visible? thats the only thing I can think of that would make it sound like the whistle is coming from both the front and rear.

 

I would get a bottle of propane with some sort of attachment to regulate the flow with a little hose on the end. You check around the intake runners,vacume hoses. Just work your way around. If you hear the rpm's pick up you found the leak. Thats the best way to find a vacume leak. The propane has a octane rating of 110 so it wont harm anything.

Good Luck

 

Did you hook up the little vacuum hose at the back? The one that runs the upper vents; do you have air blowing out the upper vents when you turn the AC or heat on?

 

Mine was making the same sound not too long back. Turns out it was my air pump so I just pulled the fuse and cleared it right up.

 

my car whistles on start up when its cold, if u blip the throttle quick it goes away

 

Do you have a BBK T/B on there. If so, one of the vacuum lines on the T/B could be your problem. On the older ones the holes inside T/B are aft of the blade. So there is suction from the motor and the T/B.

 

I'm not running a/c, nor do I have any of my smog stuff on there. The throttle body is ported and polished, but its not a BBK, I think its a ported stock TB. I almost positive that its not the TB, because I blocked off all the holes and gaps with my fingers and nothing had an effect on the whistle.

Would anyone thinking replacing the valley cover would be the solution? I am going to try spraying starter fluid around to see if the RPM's rise anywhere, but if that doesn't work, any suggestions?

John

 

Yes but even if you are not running AC you have heat right? Either way I would think you need that connection on there (little prong on the passenger side, back of manifold).

John

 

No, don't have heat either, its a track car. I will double check it and make sure, but I don't remember seeing a connection back there.

 

Is this a FAST 78 by any chance? Those suckers had a whistle caused by a protruding piece of plastic at the main inlet IIRC.

 

no, its stock unfortunately. Has anyone heard of the valley cover cracking rear the bottom seals and causing a whistle?
I thought I had seen a cracked valley cover before, I think caused my over-torquing the bolts.

 

Alright guys, I figured out how to eliminate the whistle noise, but I was wondering if what I'm doing to stop the whistle is bad for the engine.
I figured out that if I squeeze shut the vacuum hose that runs between the intake (just behind the throttle body on the passenger side) and the passenger side valve cover, the whistle goes away and it continues to run fine. Is this bad for the engine to block off those ports? What does that hose usually do? other than make my car whistle!
So, the question is, will it do any harm if I eliminate the hose?

Input very much appreciated,
Thanks,
John

 

Oh yea, and I tried the carb cleaner with no luck, I sprayed everywhere with no rpm rise... except when I did it on my air filter...

 

That's your fresh air source into the system, you do not want to block it off.

 

Well, I figured it was there for a reason, its good to know why. Thanks. As for my second thought...
What if I eliminated the hose, put a breather filter on the valve cover side, and blocked off the intake side?
Would that be ok? or does the valve cover need to balance with the intake?

John