Ok H-T, I have a 1999 Honda Civic DX with an automatic transmission. (no bashing. i will get upset with you.) Anyway, I have a Megan Racing Header and recently got 2 1/4 inch piping with a Magnaflow Powertube and a 4 inch turndown. At around 3500-4000 rpms, I hear what sounds like an exhaust leak. I've replaced the 4 into 2 gasket and the donut gasket today but I still hear an air leak. Sorry to be vague. Someone said it could possibly be a vacuum leak but I'm not so sure. This has got me stumped. Any useful input will be appreciated. BTW, I had a leak before I got the new exhaust. Just figured it was the gaskets. Thanks guys.

 

Well I was gunna consider the massive exhaust you have but you said it was already there before you put that on. I'd suggest feeling around all the vaccume lines while the car is running, so don't burn yourself, and feel for any kind of a small air leak.

 

Spray some brake cleaner around your vacuum hoses and intake mani and listen for a drop in idle

 

i'll try to do that. i mean but would a vacuum leak cause a shhhhhhhh sound at only certain rpm's like that?

 

^that's the way i look for vacuum leaks.

OP - if you have a vacuum leak, you will probably notice a high idle or an idle that hunts up and down.

once you spray the brake cleaner around the leak, the idle will level off like stock.

 

it always idles normally except when im sitting at a red light then it idles pretty low. around 500 rpms. but it's 1500 upon startup and when it warms up its 800 rpms. it also seems to lose a little power when the leak occurs. wouldn't be noticeable to anyone but me since i drive it daily.

 

if that's the case, it doesn't sound like you have a vacuum leak. keep in mind, your tach may be off slightly so it might be more than 500 (check with a timing gun).

if you're checking for an exhaust leak, it's best to get the car on a hoist and look around the piping and flanges.

any exhaust leak will show a bit of black crap build up.

 

i had it up on ramps earlier today and didnt see anything. like i said, i replaced the donut gasket and its still doing it. it drives fine and whatever leak it is only effects it when it's around 35-4000 rpms. not really hurting anything i dont guess but it's driving me insane.