"woop woop woop" sound after releasing throttle

[kalla]

I read through the archives but I didn't find any threads that mentioned a sound like this one.

BTW I just rebuilt the motor (did it myself); 200 miles on it (still breaking it in), no balance shafts. 8.5 ross pistons, eagle rods.

At pretty much any engine RPM, if you release the throttle and leave the car in gear (allow the car to engine brake), this "woop woop woop" sound comes from the engine bay. The frequency of the sound is proportional to RPM. There is a little vibration that accompanies this sound. The motor does not malfunction while making this sound, it runs just fine.

This is a pretty wierd sound, however the motor runs just fine and I have no problems with it whatsoever. It just makes this bizarre sound.

Any ideas on this one?

 

[InjenTalon96]

would be nice if u could possibly record the sound, that would help out, other then that, thats pretty weird if u ask me, i hope u/we find out what it is

 

[kalla]

I would add that the sound is not very loud (meaning it's not really all that annoying) but it *is* there, I'm wondering what the cause might be .. I'll see if I can get a recording ...

 

[Slipstream]

Check your bov. I suspect that your "woop, woop, woop" after the throttle plate slams shut is the sound of compressor surge because your bov is malfunctioning. That would explain the noise and the vibration and why it happens when you release the throttle. It's worth checking out.

 

[kalla]

The BOV (greddy type-s) is operating properly.

The sound occurs if the car was under boost or if cruising at no boost and the throttle is released, however ONLY IF THE CAR REMAINS IN GEAR - if I disengage the clutch, the sound does not occur.

 

[92Talon251]

are you sure the sound isnt comming out of the exhaust rather than the engine?

 

[kalla]

are you sure the sound isnt comming out of the exhaust rather than the engine?

Yes, absolutely sure.

On the drive home today I paid extra close attention to the sound and the vibrations that I was feeling; I then noticed that the shift lever was moving back and forth in time with the sound. I think that the only way this would happen would be if the motor was able to move forwards and backwards in the motor mounts. What I think is happening is when the motor is coasting (but in gear) it's at the whim of the drivetrain, and some small harmonic oscillations (front to back movements of the motor) are being spawned due to the old motor mounts not damping them out .. this is probably not the most desirable behavior so I think I'll go ahead and swap in some polyurethane bushings and see what happens ...

 

[timm98gst]

sounds like you may have arsenio hall syndrome

 

[adam355]

Can I get a woop woop...!?

 

[92Talon251]

Yes, absolutely sure.

On the drive home today I paid extra close attention to the sound and the vibrations that I was feeling; I then noticed that the shift lever was moving back and forth in time with the sound. I think that the only way this would happen would be if the motor was able to move forwards and backwards in the motor mounts. What I think is happening is when the motor is coasting (but in gear) it's at the whim of the drivetrain, and some small harmonic oscillations (front to back movements of the motor) are being spawned due to the old motor mounts not damping them out .. this is probably not the most desirable behavior so I think I'll go ahead and swap in some polyurethane bushings and see what happens ...

sounds possable the motor mounts could be it

Also here is a link to fix the shifter from moving backward and forward

http://www.geocities.com/qwik93awd/Vfaq/shifter.htm

 

[damentor]

Did you fix it by chance? From what you have described I think I have a similar problem.

 

[kalla]

Just to update on this, I did go ahead and pull the cover off the transaxle to check the bolt, per the vfaq. It was good and tight, so no trouble there. I might add that pulling the cover off the DSM transaxle is way easier than the 3000GT VR-4 that I used to have, doing that one was a PITA. Glad I sold the VR-4 and got the DSM.

That leaves the motor mounts as the most likely suspect, I'll update again once I have a chance to get a good look at them.