Low Freq Acoustic Resonance
#1
Low Freq Acoustic Resonance
I just bought a new 2009 Vette. It has the optional high performance exhaust system. At idle or in Drive when stopped at ~550 rpm it has a very strong and disturbing acoustic resonance at ~38 Hz. As soon as it starts to roll and the engine rpm goes up the frequency increases and the intensity dramatically decreases. My dealer tells me they will look at it. I earlier rented a Hertz ZHZ with the same exhaust set up and it did nothing like this. Thoughts and suggestions would be welcome. This acoustic resonance really hurts!
Gerry
Gerry
#2
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If you hold the car in 2nd gear and the "acoustic resonance" increases at you get to 1600 rpm and then decreases above that then I'd guess you have a problem with the control system on the NPP exhaust system keeping it in the open, unmuffeled mode. At idle, look into the exhaust outlets and the butterfly flaps in the center pipes should be closed. If they are not, that's the problem.
#3
If you hold the car in 2nd gear and the "acoustic resonance" increases at you get to 1600 rpm and then decreases above that then I'd guess you have a problem with the control system on the NPP exhaust system keeping it in the open, unmuffeled mode. At idle, look into the exhaust outlets and the butterfly flaps in the center pipes should be closed. If they are not, that's the problem.
The flaps should be open before you start the car, then close once the car is started and is idling. I think they are programmed to open at 3200rpm.
#4
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St. Jude Donor '09-'11
The NPP does have a little bit of resonance at idle. It is much more pronounced (and obnoxious) if the NPP fuse is pulled. In the normal functioning case with the butterflies closed, it stops as soon as you come up above idle speed.
What you describe is very much like a non-functioning NPP system (fuse pulled/blown or components malfunctioning). Search for CAGS LED fuse and look for the images of where the fuse is in the engine compartment fuse box, and try swapping it to see if that helps.
What you describe is very much like a non-functioning NPP system (fuse pulled/blown or components malfunctioning). Search for CAGS LED fuse and look for the images of where the fuse is in the engine compartment fuse box, and try swapping it to see if that helps.
#5
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St. Jude Donor '15
"In honor of jpee"
550? You mean your car idles at 550? Mine, stock, doesn't go below 650-700. Is this an automatic, and if it is, is that a normal idle?
#7
Race Director
Start the car up and then get out and go around back and look in the exhaust tips.
The valves will be open before starting the car (no vacuum to close them).
After you start the car and it's at idle, the butterfly valves should be CLOSED.
If they're not closed at idle, either the fuse is blown, or there is a leak or loose line somewhere.
You should not get a drone if the valves are closing properly at low RPM.
Bob
The valves will be open before starting the car (no vacuum to close them).
After you start the car and it's at idle, the butterfly valves should be CLOSED.
If they're not closed at idle, either the fuse is blown, or there is a leak or loose line somewhere.
You should not get a drone if the valves are closing properly at low RPM.
Bob
#8
The NPP does have a little bit of resonance at idle. It is much more pronounced (and obnoxious) if the NPP fuse is pulled. In the normal functioning case with the butterflies closed, it stops as soon as you come up above idle speed.
What you describe is very much like a non-functioning NPP system (fuse pulled/blown or components malfunctioning). Search for CAGS LED fuse and look for the images of where the fuse is in the engine compartment fuse box, and try swapping it to see if that helps.
What you describe is very much like a non-functioning NPP system (fuse pulled/blown or components malfunctioning). Search for CAGS LED fuse and look for the images of where the fuse is in the engine compartment fuse box, and try swapping it to see if that helps.
#9
If you hold the car in 2nd gear and the "acoustic resonance" increases at you get to 1600 rpm and then decreases above that then I'd guess you have a problem with the control system on the NPP exhaust system keeping it in the open, unmuffeled mode. At idle, look into the exhaust outlets and the butterfly flaps in the center pipes should be closed. If they are not, that's the problem.