My 88 T2 makes a hissing noise from within passenger floor - not there at cruise, you can hear under light to medium acceleration (no boost) and then it's gone when under boost.

I was thinking air pump, or vacume leak but what's up with it stopping when I'm in boost.

I'd appreciate anyone's thoughts

 

exhaust leak

 

One of my muffers is shot from the inside could I hearing the effects of that? It's definately coming from inside the pass floor area.

 

yeah I would also look around the cats... maybe something burnt through there

 

I'm thinking the air pipe to the cat. That's known to go. And I don't think the air pump works too well under boost

 

I just got back from a drive and you can notice that the hissing is robbing power very slightly. When slowly accelerating at constant throttle it stops around 4000 rpm and you can feel more power kick on like a switch. I'm thinking vacume leak or like fingers said that air pipe out of the main cat that I think is for emmissions.

Thanks for the reponses & please more imput

 

I had a hissing sound yesterday till i found the HUGE *** hole in my back tire.. $#%&! iT deflated in under 3 minutes!

 

if the split air pipe was off, you would be able to smell it.

 

that 4000rpm kick is just the common 3800rpm hesitation. it does this because the secondary injectors come on around these rpms and because of bad grounds it causes the kick.

does the hiss sound like a slight sucking, or is it a sharp high-pitched sound?

 

LOL. Not relevant, but humorous......

 

That hiss sounds like it's the split air pipe. If you have a series 4, your secondary ports depend on the backpressure from that in order to open. You would experience degraded performance if that split air pipe is leaking

Take it to a muffler shop, have em raise it on a hoist. It wont cost you a dime, but they can show you where the problem is.

 

that was my bov you heard as i flew by.....haha

 

Thanks guys!