Mass air hum

Pnyxprz02 · Jun 29, 2010

Hey guys i have a 2002 GT and i keep hearing this electrical buzz or hum coming from the mass air meter. I just put on a PPI lower intake and thats when it started making the noise. Ive checked for air leaks everywhere but cant find any. Whats weird is it only does it at idle but not everytime. Any of you guys out there had this problem or know what is going on? Thanks

trinity_gt · Jun 29, 2010

It's resonance. Remember, although it seems like air is drawn into the engine smoothly it's occurring because of impulses caused by intake strokes. At idle with the engine at 750RPM (for example), the engine is turning over 12.5 times per second and each time it turns, 4 of the engine's cylinders' intake valves open and draw air in, giving a 50Hz impulse frequency. This is probably what's exciting the intake: It's possible that the PPI (not sure which intake this is, never seen it...) has additional length that just happens to resonate at this frequency, causing other bits to vibrate.

Modern OE intakes have all sorts of resonance chambers and volumes designed specifically to eliminate or tune certain frequencies. The OE Mustang intake had a rubber "silencer" that extended into the fenderwell. There's actually a fair amount of science that goes into removing objectionable noises from engine intakes. When you go low-restriction, cold-air yada yada, a lot of that engineering and science ends up in your spare parts bin

trombonedemon · Jun 29, 2010

trinity_gt said:
It's resonance. Remember, although it seems like air is drawn into the engine smoothly it's occurring because of impulses caused by intake strokes. At idle with the engine at 750RPM (for example), the engine is turning over 12.5 times per second and each time it turns, 4 of the engine's cylinders' intake valves open and draw air in, giving a 50Hz impulse frequency. This is probably what's exciting the intake: It's possible that the PPI (not sure which intake this is, never seen it...) has additional length that just happens to resonate at this frequency, causing other bits to vibrate.

Modern OE intakes have all sorts of resonance chambers and volumes designed specifically to eliminate or tune certain frequencies. The OE Mustang intake had a rubber "silencer" that extended into the fenderwell. There's actually a fair amount of science that goes into removing objectionable noises from engine intakes. When you go low-restriction, cold-air yada yada, a lot of that engineering and science ends up in your spare parts bin

Now that you mention it, when I was putting a CAI on my; now recked Honda Civic, there was so much extra crap on the intake, like a plastic baffle that looked like really big car horn.
To the OP, you don't think that sucking air sound is mean sounding? Thats what the Old School guys did w/there air filters, they turn the top upside down to get that rumble and sucking sound!
Great explaination Trinity!

Pnyxprz02 · Jun 29, 2010

Thanks for the information but not sure I explained it correctly. Its not a sucking in air type sound at all. It occurs only at idle but goes away after giving it some gas. Its also a constant tone that isnt always there. The intake i put on it was the PPI Typhoon that is a direct replacement for the car. Just tired of this annoying beeeeeeeeeeeeeeeeeeepppppppppppppp thanks

trinity_gt · Jun 29, 2010

Resonance of that sort is going to sound like a hum or constant tone. If you've ever heard 60Hz mains hum in a stereo system's speakers, it's probably not far off that.

Check to see if there's any loose or flexible bits on the intake that may be vibrating sympathetically. Put your hand on the intake at various spots to see if you can make it go away or damp it. If not, if the sound is coming out the air filter itself, you're either going to have to live with it, add a resonance chamber to the intake to alter the resonance characteristic of the intake or swap intakes with another brand.

Mass air hum

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