Time to troubleshoot a hiss (possibly EGR related).

[Whisper]

This started happening after ZE went in, with headers, high flow cat (meow), etc.

Been like this for a couple of years now, but I was always too busy with other parts of the car to sort this out.

Anyway, what happens is if I rev the car and then lift off the throttle, as the RPM drops, there's a continuous hissing sound coming from what seems to be back side of the motor, exhaust area... This hiss also corresponds with certain hindrance in performance. Specifically, at WOT as the car is under load, I can hear it a little bit, but it is most severe when I lift off the throttle in higher RPMs, and as it hisses I experience some major engine breaking.

Now, I don't know how much engine breaking ZEs with a stock flywheel do at higher RPMs, but it seems I get a bit too much.

It goes like this.

1. In gear, rev to say 4K or 5K - no hiss unless WOT
2. Lift off the gas completely, still in gear - for a moment there's complete silence and no engine breaking
3. After a moment of silence - very loud hissing (think turbo blow-off, only continuous) and the car bucks forward pretty severely, as if I dropped the clutch, and then massive engine breaking as car rapidly decelerates

I don't experience this when I'm cruising slightly on the gas, but if I lift, I hear it.

Somehow I feel this might be EGR related or something of the sort, because I'm not sure what else it could be. I checked all my vacuum lines and connecitons, and found no leaks.

[Daveb]

You should probably hook up a vacuum gauge & see wat you are getting.

You sure you didnt use a real cat, Hisss Meow

[Whisper]

If it were a real cat it'd be hissing all the time, though.

[Daninski]

Did you connect the ERG so you wouldn't get a code? If so below the TB on the block is a spot for an allen key head bolt. It's on your K8 if you go look. If you don't install the bolt into that hole it will vent exhaust from the EGR. I had a pic somewhere, if you need it I'll find it.

[Whisper]

Yeh, wanted EGR hooked up for emissions reasons as well. I'm not getting a code, so I assume it's hooked up somewhat correctly... I'll look for the bolt, but if you can find a pic, post it up, so I have a better idea of what I'm looking for.

I don't have the K8 anymore, so I can't check it out on a bare motor.

[Joey's mx]

I am also having this same problem!!

[onlytrueromeo]

+1 people in my car think it's a BOV LOL.

[Whisper]

Did not find anything. No leaks. EGR seems to be in order.

Guys at the shop looked at it as well, said it's coming from exhaust ports area, most likely air resonating through headers and downpipe at certain velocity. Possibly because of the way headers are bent, or some such. I'm assuming you guys have headers as well, eh?

I'm just going to accept that as a valid answer for now and not worry about it.

[onlytrueromeo]

I have 2.25" piping w/ headers, but I don't know how it'd be the exhaust hissing like that...hmm.