Loud ass hissing noise
 

91 Naturally Aspirated

Drove and sounded fine on the way to work this morning and at lunch. On the way home however, I hear a loud ass hissing noise (can't figure where, tried for about an hour). I also have no power. It still feels smooth, just no fucking power.

I have the factory emissions in place. Any ideas?

might be a bad vacuum leak somewhere

where would i look for the vac leak? It does sound like one, but idles fine.

A vacuum leak big enough to be heard would result in a crappy idle. Where in the band is the car lacking in power - top end or everywhere? Did the S5 NAs use pressure from the air pump to operate aux ports/VDI; maybe the hiss is from an air pump plumbing leak?

It may be airpump. I do believe it was used for aux port operation. I'll see if i can figure out where it could come from and check it tomorrow

Can it be heard while reving in neutral?

yes

Is this noise heard at all times or under load?

yes, its there all the time

It appears to be coming from the header to downpipe connection? Could my cat have melted and blocked cause it feels like anything above 3k is where the lag is. I may try to pull it tomorrow morning and see if it looks free and clear.

I tested all the variable intake valves and went over all pressure and vacuum hoses, and they all worked and were in good condition.

Melted cat is a good possibility, the best theory I have heard so far.

It was the cat, i got pictures to post later. I gutted it and put it back in, im up and running again like ot should be

pulled the cat and saw it wasn't being a good girl
http://i44.photobucket.com/albums/f4...A/badkitty.jpg

so i punished it
http://i44.photobucket.com/albums/f4...ishedkitty.jpg

Haha nice...I almost gutted my cat but I don't wana buy another for echeck

Yeah, I have seen the plugged cat before (several times) unfortunately, I had to replace it (emissions). I think that the guts may have fallen out lately though, as I noticed the car being a little louder. If I don't look, then I don't know....

Glad you found the issue!