what did they do to the car?

I recently got my Chev Impala (2001, 70,000km, out of warranty) to the selling dealer as the car developed some kind of "air sucking" noise on
acceleration (it sounds more like whistling on hard acceleration, pretty loud). It's much like the problem I got years ago with another old car - bad catalytic converter.
But the result is so frustrating. The dealer says they did lots of testing including on vacuum and catalytic converter, but found no problem! They say this could be normal because some of their brand new Impala's have the same noise. So just charged me 1.5 hour labour, that's it.
Taking the car back, the air-sucking noise is louder, and something else is wrong - the car lost a lot of acceleration power! The car used to be very powerful when accelerating, but now it's tough to gain speed, especially getting onto highways. I have to step hard on the gas pedal, the engine making big noise, still quite slow to get speed up. I'm wondering what the dealer do to check on the problem, making the thing even worse. I'm sure, if I get back to them, the answer is still "normal".
There are only a couple of Chev dealers in this small canadian city, I do want to have some advice before taking the car to the other dealer or another mechanic. Thanks in advance.
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Have them drive the car and feel the loss of power and go from there, if it is evident to you, they should feel the problem and be able to diagnose it.

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Simon wrote:

Pressure test before and after the cat.
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Thanks. So, if the pressure test is ok, the whistling noise must be from somewhere else, other than the cat.?

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Simon wrote:

Probably. A clogged cat would give the symptoms that you described but should have been easily found by the tech.
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Simon, during 45 years around cars, I've seen about as many separated exhaust pipes(not tail pipes!) as stopped up convertors. These pipe-interiors are dual-layer pipes and the interior wall can separate, peel into the center, and obstruct exhaust flow. One way to substantiate: use a drilled hole and something like a steel gas-welding rod to fish thru the test opening and find the obstruction. Re-weld failed test holes. Usually, it peels away such that pushing the rod from front-towards-rear shows up the obstruction. Of course, simplest way is to disconnect the pipe end and try pushing say a garden hose thru from front-to-rear. We've had perfectly healthy-looking pipes separated and causing loss of power and that swooshing sound as you attempt to accelerate. Simple to repair, at the muffler shop; maybe a little more analysis finding the exact location. HTH, s
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Don't know of any manufacturer who uses a double wall pipe in an auto. Motorcycles yes. It is possible that the muffler itself has gone bad though.
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sdlomi2 wrote:

I experienced this very thing on a two year old '73 Chevelle. The mechanic who diagnosed it said it was probably caused by driving through cold water laying on a side road I had went down while on an early spring fishing trip. As I recall, the car sounded fine when I parked it, and a few hours later when I started it and pulled away the noise was suddenly there. He showed me the pipe when he removed it and sure enough the inner pipe was folded in on itself.
Jack
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Greetings, Jack. Strangely enough, we had 2 relatively low-mileage'73 Pontiacs experience that problem in a short time period. When the 2nd one appeared, we went straight to the problem--took a little longer on the 1st one, tho'. Could've been a defective supplier for that model year?!? (At the time, we were buying over half our used-car supply from a Pont/Mercedes dealership.) s
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Seeing my other reply, the testing dealer could have somehow pushed the peel further into a closed position--possibly just by driving and excess flow bending the peel further into an obstructive position. It will probably get worse--and is NOT GOOD for your engine! Repair should be urgent. Driving should be minimal--like ONLY to the muffler shop, and slowly when doing THAT. Luck to ya! s
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Thanks a lot. I was just desperate about it.
The thing is the cat. converter is on extended warranty (8 years) by GM. It has to be a Chev dealer to fix it for the warranty. As you suggested, I just called a local MIDAS muffler shop, they say they can do an emission test (free, surprise). I hope they can offer some kind of proof that the converter is bad, then I can talk to the dealer again. But I'm afraid they will do the same as the dealer did. As another reply mentioned, whether a cat. is bad or not depends on pressure test on both ends. Is the pressure test really dependable?
Anyway I'll print off your messages and show them... Thanks again. Simon

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