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Discussion Starter #1 (Edited)
2001 Alfa 147, 60k miles
I am getting 14 mpg in city driving and maybe 23 outside the city. I am not a spirited driver and I get these figures by running very very gently. All readings are according to the trip computer.

Plugs, filters, leads are all less then 2 yrs old.Thermostat is OK, car gets to 90C in a matter fo minutes and stays there
MAF is ok, MIL light is not on so the lamdbas are supposedly ok ?

One thing though, when I took the exhaust off there were some ceramic bits flying out of the main cat and from the two precats. Not many bits and not large in size though.

Can anyone give me a hint on what to check next ? This is really crappy MPG.
 

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Discussion Starter #3
As I said, it gets to 90C quickly and stays there even during long runs. On long engine brake downhill descents it drops to ~80 on the gauge
 

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You're trip 'puter is probably lying to you (mine say that I get 53 mpg !!!...) do a brim to brim test and see what sort of results you get ...
 

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Discussion Starter #6
Ok, thanks for the input. The fuel gauge seems to drop in line with this horrible mpg, but will try the brim solution
 

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I reckon I get about 60-70 miles on a tenner.

at 4.55 litres per gallon..... pluto lined up with uranus.... the wind in the right direction....

Thats about 30mpg (ish) from my 156 2.0TS.
 

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2001 Alfa 147, 60k miles
I am getting 14 mpg in city driving and maybe 23 outside the city. I am not a spirited driver and I get these figures by running very very gently. All readings are according to the trip computer.
I don't normally trust the car computer, but the one on our Clio is pretty accurate! But I still do the brim-to-brim check ... You ought to get in the region of 300-320 miles from a tank, which is about 28-30 mpg. Maybe more on long runs and with a light right boot.

Running the climate control?? That will hit it as will driving with windows down, roof racks, sunroof open, etc ...

Plugs, filters, leads are all less then 2 yrs old.Thermostat is OK, car gets to 90C in a matter fo minutes and stays there
MAF is ok, MIL light is not on so the lamdbas are supposedly ok ?
Not necessarily. My lambda is shot (AlfaDiag traces show some weird results!) but the management light has never come on because of it ... even when the original died ...

One thing though, when I took the exhaust off there were some ceramic bits flying out of the main cat and from the two precats. Not many bits and not large in size though.
Doesn't sound right but that shouldn't cause MPG problems ...
 

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I get about 32mpg in my 2.0TS according to both the computer and working it out with the brim test. It means I get about 400 miles out of a tank. This does drop quite considerably when I get over excited with the right foot :eek: but the mpg is still normally in the high 20's.
 

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2001 Alfa 147, 60k miles
I am getting 14 mpg in city driving and maybe 23 outside the city. I am not a spirited driver and I get these figures by running very very gently. All readings are according to the trip computer.

Plugs, filters, leads are all less then 2 yrs old.Thermostat is OK, car gets to 90C in a matter fo minutes and stays there
MAF is ok, MIL light is not on so the lamdbas are supposedly ok ?

One thing though, when I took the exhaust off there were some ceramic bits flying out of the main cat and from the two precats. Not many bits and not large in size though.

Can anyone give me a hint on what to check next ? This is really crappy MPG.
Are you working it out in miles to the gallon or kms/liters. If your in kms you should do roughly 480 - 520 kms before refills if you fill it up. I would not trust the board computer. I watched Clarkson/ topgear driving the Jag to Blackpool i think that according to his computer he had theoretically run out of a fuel 100 miles earlier and he was still driving. (PS you do know it has 5 gears l;)
 

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Answer is in your question m8... The break up of a cat be it any bit, small or large can cause blow through or even worse a blockage. They need a good seal, just like an air filter would.
I had the very same issue on a citroen C5 1.8 that was getting at best 17mpg! (normally 42 mpg) with a cat that had collaped too without any noises or warning signs etc... The first thing I knew of it was the worsening MPG then eventually a tell tale rattle from a collapsed baffle in the middle silencer, caused by the the cat breaking up in chunks.

However, you could try a straight through cat bypass pipe for now to see if it improves, it will be louder and probably quicker but make sure that the rest of the silencers arent suffering any blockages
 
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Wouldn't a failing CAT also show signs of the engine being underpowered? - There is no mention of this :confused:
Are all the breathing 'hoses' tightened properly?
Would be worth having a diag to check lambda readings as they affect the whole running rich / lean aspect of the engine
 

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Discussion Starter #13
Wouldn't a failing CAT also show signs of the engine being underpowered? - There is no mention of this :confused:
Are all the breathing 'hoses' tightened properly?
Would be worth having a diag to check lambda readings as they affect the whole running rich / lean aspect of the engine
I have double checked all of the hoses and they're fine.

It does feel underpowered, especially below 3000 rpm. I think i need a diag to check the mixture.

However, if you remove all of the ceramic bits in a cat isn't that equivalent to a straight pipe ?

Can you clean the lambda sensors?

I would have expected the MIL light to be on whenever a rich or poor mixture is detected by the sensors (at the right engine operating temp, of course)
 

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Well.... There is still the honeycomb tubing inside the cat body itself and the ceramic is used to hold it in place since ceramic doesn't expand you see. Yes you can clean lambda (o2) sensor but it doesn't last that long if there is an underlying issue.
The MIL should come on but it all depends if the problem lies before the o2 sensor or after it.
Alfa diag should give you some idea where to start looking though
 
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You can bash out the inners of a CAT - dunno what will happen @ MOT time over there though

Cleaning a Lambda is like cleaning a MAF - it only puts off the inevitable

Lambdas do not always illuminate the EM light, but a diag would give you readings

:)
 

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Fuel economy issues or not, underpowered or not, you are getting ceramic out of the tail pipe. Unless you are adding wedgewood additives, its the CAT.

I would try Ronnys cat bypass pipe as the most cost effective remedy. If it works, great. A bit more noise, bit more power, all good. Then you can get a replacement cat at leisure to keep the nice ministry man happy.
 

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Discussion Starter #18
More cost effective to bash out the inners then ;)
Yeah, as far as I know, this being a EURO3 machine, the first two O2 sensors -one for cyls 1&2 and the other for cyls 3&4- read oxygen levels before entering the precats. The third O2 sensor then reads the O2 levels from the processed gases and if they're out of bounds on goes MIL.

I'm in for a diag these days, will let you know
 
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