Empty cat..?!

D.Slatford · Post by **D.Slatford** » 29 Jan 2003, 23:37

Just had my 95 Xantia 2.0i 8v MOT'd, and told it needs a new cat. Well, it's been two years since I bought the car, at which point it was supposed to have had a new one fitted, so didn't have much choice (grrr, MOTs)
The puzzling thing was though, when I picked the car up, I was told the old cat wasn't just shot - it was completely hollow! No trace of it's innards at all. It passed the MOT just fine last year, at the same garage too. Is it remotely possible for the thing to shatter and shoot itself out the exhaust, without me knowing anything about it? It does sound very improbable.. but then so does having an empty unit for two years and it going unnoticed.
This might tie in though with the lack of efficiency in recent months, I've been getting around 100 miles per 20 litres of petrol, which can't be right. How would an empty cat affect efficiency? Would it improve it or worsen it? I've been hearing conflicting ideas. But the lack of back pressure and possibly different readings from the lambda sensor resulting from that will affect the engine somehow? The engine definately feels different to drive now, more how I remember it, I barely have to touch the accelerator to cruise along. I'm sure I had to give it a lot more gas before. Can I expect more or less milage now?

jmd · Post by **jmd** » 30 Jan 2003, 22:58

It seems that the absence of a Cat went un-noticed during your previous MOT,I have read of a case where the cat broke up in a car and somebody emptied out the broken pieces,reconnected the exhaust and continued on.Perhaps the previous owner of your car did this,or paid for a Cat he did'nt get.I expect you would achieve extra MPG without a cat-convecter(Disconnect the Lambda sensor,and see if you improve your MPG)
Edited by - jmd on 30 Jan 2003 18:01:15

alan s · Post by **alan s** » 31 Jan 2003, 02:03

My son does a lot of work on racing cars & grey imports and he often speaks of "high flow cats." I never asked the full story but I assume he isn't refering to the neighbours ginger toms urinary tract infection so I'll ask the question when I see him in the next few days and see how it compares with your problem & post his response.
Alan S

D.Slatford · Post by **D.Slatford** » 31 Jan 2003, 05:32

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
My son does a lot of work on racing cars & grey imports and he often speaks of "high flow cats." I never asked the full story but I assume he isn't refering to the neighbours ginger toms urinary tract infection so I'll ask the question when I see him in the next few days and see how it compares with your problem & post his response.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>
Thanks. Generally the opinion seems to be, cats restrict the exhaust too much, which is bad for performance. The garage mentioned something about lack of back pressure though without one, effect this has on compression, and effect it has on lambda sensor readings. I would assume the ECU be configured to expect the presence of a cat, and thus certain back pressure. I'm not too interested in performance, only economy. Removing it may not simply "make it run better" due to all manor of factors?
That said I've noticed with a new cat the engine does seem to run smoother, glides along with only the slighest of slight touches on the accelerator.
Also affecting my low MPG is probably the thermostat, on average the temperature is a little over 70 which seems cool (I have a replacement thermostat to fit), and I'm now wondering if my hydrolic pump is wearing out too, imposing it's own load. Power steering is very stiff now the weathers turned cold, that is until the cars heated up a bit...

wheeler · Post by **wheeler** » 01 Feb 2003, 20:56

i recently removed the insides of the cat on a mates saxo VTS due to it starting to break up & rattle,since it was removed he has reported better performance & fuel consumption.lack of a cat should not affect the sensor readings as it takes its readings before it passes through the cat(only the new EOBD engines have 'before & after' sensors.disconnecting the sensor will probably bring the'K'light on and it will run with a downgraded fuel setting