Clogged catalytic converter?

Hi everyone ... Our 1999 MK1 Punto Sporting 16V is having some really serious power issues. Over time, it has got worse and worse and since the last service, there is a noticeable, if not dangerous power drop when
shifting the third and beyond. The car needs to be driven with the foot to the floor and despite the revs going up reasonably quickly, the car could not pull skin off custard!
Just to recap, the plugs and wires have been changed at the last service and the air filter, fuel filter and oil filter/oil were changed at the last two services. After the last service, the car had a noticeable "jingle" when shifting gears ... Not every time, but most times. I thought nothing of it until the last week when I was reading about dropped baffles and clogged cats on another car forum.
That got me thinking ...
So, how do you check for a clogged cat? I have read a couple of technical websites which suggest doing a vacuum check and revving to 2500 RPM. I have connected a gauge to the only vac line I can find in the engine, which is the FPR vac line. I t'd the gauge off that line and found 19 inches of vacuum at warm idle. Revving the engine got the just up to, like 5 inches of vacuum, and then holding at 2500 RPM made a reading of 25 inches of vacuum. According to one site, "You can do a vacuum check at idle and then at 1500 RPM. If the vacuum is say 21 inches at idle and like 15 inches at 1500 then the cat is likely clogged." So ... Does 25 inches mean it's super-clogged, or okay?
Can anyone give me any hints?
Paul
1999 Fiat Punto Sporting 16V (Mk1) And some SAABs :) ... http://saab.go.dyndns.org
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Of course you could remove the cat and replace temporally with a piece of tube, two saw cuts to make a split, worm drive (Jubilee) clip to fix. See how it goes on a drive to the breakers yard with the old one, to see if they have one that fits.
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in article snipped-for-privacy@pipex.net, ato snipped-for-privacy@hotmail.com at ato snipped-for-privacy@hotmail.com wrote on 23/07/2006 08:59:

I think I answered my own question about the vacuum measurements. Vacuum should be the same as or more vacuum when the revs are increased. Of course, the vacuum gauge will jump up to, say, 5 In Hg when the throttle is first pushed. So, the vacuum diagnosis does not show it to be clogged.
That said, in an experiment similar to your suggestion, I drove the car a short distance with the exhaust removed from the end of the exhaust manifold and a pipe swept out to the side of the car. It felt a lot more urgent and much more like it should perform.
The exhaust is definitely hotter pre-cat than after the cat when the car is warm. Does that indicate a failed cat? The car also performs a lot better during its warm up than once it is warmed up. If I listen really really carefully, at low speeds (with someone walking alongside) where the engine vacuum changes rapidly (say, stamping the throttle and letting off), there is a definite jingling to be hard further towards the back of the car. I wonder if there's a dropped baffle or something in one of the muffler boxes.
I'll continue to experiment, but TBH, I'm getting a little sick of it and I think I'll just sack the lot and get a decent stainless exhaust and take advice from the exhaust experts as to the catalytic converter. I just like to "have a clue" before going to those kind of places so it appears I know what I'm talking about :)
Cheers,
Paul
1999 Fiat Punto Sporting 16V (Mk1) .. and some SAABs :) ... http://saab.go.dyndns.org
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Temperature measurements are a bit difficult to interpret. The cat itself generates heat as part of its action, but like any surface there is a cooling effect. Usually the cat has a protective shield and it has been known for the cat to start a fire, if parked on long dried grass during a drought.
Vacuum tends to measure how hard the engine is working, which relates to throttle opening. Throttle wide open like when accelerating, max power, and it's difficult to pull a vacuum with the inlet manifold wide open.
Downhill trailing throttle, no power, engine braking, throttle closed and engine acting as a vacuum pump, max vacuum.
Vacuum gauge is best interpreted under actual driving conditions, rather than just revving a stationary vehicle. Since a blocked exhaust would mainly affect max load conditions, when the vacuum is low, it's a bit hard to correlate with vacuum readings.
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in article C0E92059.46B0% snipped-for-privacy@blueyonder.co.uk, Paul Halliday at snipped-for-privacy@blueyonder.co.uk wrote on 23/07/2006 12:47:

Hi Guys'n'Gals ...
Following on from this, our mid-muffler finally fell off. Now it's replaced, the car has every bit of power and urgency it had before. It's brilliant! I can't believe how quickly the revs rise ... What a blast!
So, that mid-muffler mid have been the problem. We've replaced all the rest of the exhaust since it first snapped just in front of the mid-muffler - manifold, down pipe and rear section.
Cheers all, Paul
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