My Chev Impala 2001 base (57K) has been making hissing noise at
acceleration. The noise came into the cabin from front somewhere down under
the hood. Got it checked by dealers/mechanics for 3 times. They all say "no
problem." or "normal". I know they must have checked cat convert and vacuum
leak etc. But the hissing has been louder and louder when accelerating even
at very low speed. Another symptom is poor acceleration and a little worse
gas mileage together with the hissing noise coming up a few months ago.

I'm just wondering if this could possibly be due to a leak somewhere in the
emission system other than a plugged catalytic converter? a loose joint in
exhaust? The noise does sound like air/water spraying out from a high
pressure pipe. Would it be wise to get the car back to dealer again, and
just ask for a check on exhaust?

Thanks!

An exhaust leak usually has a rumbling sound. You will likely be able to
hear
it even at idle. A hissing noise doesn't seem right for a leak...

Just because you took the car to a mechanic, it doesnt necessarily mean
that he checked anything at all. Maybe just gave you an opinion.

An exception to this is a hole in the tailpipe past the muffler. My father
had a piece of rotted tailpipe blow out ounder hard acceleration on a
Suburban and it hissed/swished on hard accelration.
Roy
<HLS (AT) nospam (DOT) nix> wrote

Dave wrote: