Intermittent hissing noise from engine bay

[alexchannell]

Sometimes (bout 1 out of every 10 times) when I'm accelerating (can be WOT or not) there is a hissing noise in the engine compartment.

When it happenes:
starts around 4000 rpm
sometimes lasts a second or two, sometimes just a burp
no noticable power differince
sounds like a very aggresive vacuum leak (sucking)

any thoughts?
The car is in great shape with 49k miles and meticulously maintained. The throttle body was recently cleaned (by me) but the noise remains. All tubes/hoses looked in good shape.

edit: oops, this should probably not go in DIY?

 

[hofffam]

I'm a new owner and hear a similar noise when accelerating. It goes away when I ease up on the pedal. I think it is the intake. I'm a bit confused how that works - it seems like it should be "sucking" most of the time, not just some of the time. My NSX has an aftermarket intake (Cantrell) with the OEM airbox.

 

[rbirling]

I definately hear a lot more sucking type noises with the AIS. I'm wondering if you might be hearing the induction system switchover around 4800?:

http://www.nsxprime.com/FAQ/Technical/vvisinfo.htm

 

[Scin]

This is probably just intake noise. You usually wouldn't notice this with a stock air box/filter and scoop.

Do you have an after market scoop or intake?

Mine will hiss at partial throttle at certain RPMs (downforce scoop, unifilter).

 

[alexchannell]

This is probably just intake noise. You usually wouldn't notice this with a stock air box/filter and scoop.

Do you have an after market scoop or intake?

Mine will hiss at partial throttle at certain RPMs (downforce scoop, unifilter).

All stock.
It is quite loud when it happens, definatly not intake noise. Very on-off in its nature, it doesn't gradually get louder or anything.

 

[Scin]

There is a relay for the fuel pump that is rather loud. The relay kicks the fuel pump into high gear at a certain RPM (somewhere north of 4,000, forgot where exactly).

The relay would be more of a clicking noise, could this be it?

 

[alexchannell]

There is a relay for the fuel pump that is rather loud. The relay kicks the fuel pump into high gear at a certain RPM (somewhere north of 4,000, forgot where exactly).

The relay would be more of a clicking noise, could this be it?

Nope, definatly a sucking (sometimes prolonged sometimes not) definatly not a relay.

 

[Scin]

Nope, definatly a sucking (sometimes prolonged sometimes not) definatly not a relay.

Warm your car up, put it in neutral and set the parking brake. Then open the hatch and manually feed it throttle by pulling on the cable/lip where it connects to the throttle body.

While you do this check for any leaks, make sure the boot between the throttle body and air box is well sealed, and that you cannot see any obvious other vacuum leaks.

It should at least give you a better idea of where the sound is coming from.

 

[alexchannell]

Warm your car up, put it in neutral and set the parking brake. Then open the hatch and manually feed it throttle by pulling on the cable/lip where it connects to the throttle body.

While you do this check for any leaks, make sure the boot between the throttle body and air box is well sealed, and that you cannot see any obvious other vacuum leaks.

It should at least give you a better idea of where the sound is coming from.

Thanks, already done that. I can't replicate the noise when not under load unfortunatly....I'm out of ideas.

 

[DDozier]

Thanks, already done that. I can't replicate the noise when not under load unfortunatly....I'm out of ideas.

You could find a Dyno shop and see if you can do it under load on the dyno.

Dave