I've heard of problems on this forum with back pressure and lamda probes not working properly afterwards. You can get some non alfa spares at reasonable prices....:tut:

 

Hi. Had the same problem on mine 2 years ago. Mine was the rear cat (there are two others just below the manifold I think). Had a non Alfa part fitted for £185 at a local exhaust centre. So the £1200 you have been quoted seems a bit steep! With scrap values as they are at the moment it might pay to try to keep the old cat & take it to a scrap yard. I'm told they're worth around £50 as scrap. Another alternatve is to look fo a good secondhand one on eBay. I saw pair of front cats go a while ago for less than £100. You shold be able to work out which one is rattling quite easily. Good luck

 

Thanks for your replies.
Since my cat is hosed (at least the main one is, not sure about the pre), i am thinking it may be time to spruce up the ride a little: those new diesel engines sure are giving my bella a run for her money.
Sure, there are less drastic ways of making my car go faster, and i wouldn't be thinking of de-cating my car if the cat was in working order, but if the less expensive way of fixing the noise my broken cat is making happens to give my car more torque and power, i'm inclined to try it out. If things happen to go wrong, no major loss.

That's why i was asking about lamba probes: i read here that you may need to ground them in order to fool the ECU into thinking the cats are still doing their job. How would i go about doing this?

 

Not quite as simple as that I'm afraid. It's a bit of a pain.

Your best option is to get a sports cat.

The precats are fine, you can loose them easy enough. The supersprint manifold is £481 and the CSC is about £420 I think)

The SS one already has holes for the front lambdas.

 

Whats the chance of changing out the 2 pre cats and keeping the main cat and still passing the MOT/NCT?

Keeping the lamda reading happy is a different issue i know, but from an emmissions point of view, is it plausible without swapping from one to the other just for the test?

 

You should be able to take out the pre-cats for the manifold ok. I think the rear lambda would throw a fault code though as there are no cats between the front and rear sensors. Some sort of resistor should be available to cure it though.

 

Definately get lamda errors but as you said, ways and means around that. Mainly would be worried about emissions failure...

 

not if you only remove the pre cats.

 

Have just been through all this myself. Your best bet for the main cat is www.cats4less.co.uk - £150inc vat. Especially if that part is brand new the lamdas aren't gonna know if the pre-cats are faulty.

Replacing the pre-cats alone is more or less impossible unless you are a very creative welder or without blowing 500 quid on the supersprint catless downpipe.

To decat completely will pose you big problems because of the post cat lamda. The simplest solution would be a remap. You could TRY some very creative electronic work with resistors to fool the existing map into thinking that all is still well, but am almost certain that will put your management light on (and destroy any performance gain) because depending on engine conditions the two pre-cat lamdas will read at odds with the constant 'resistorised' reading of the post cat. Don't forget you NEED lamdas with an electronic engine in order for it to work properly.

To knock out the centres with a big stick isn't something I seriously considered: the back pressure will be all over the place, the noise will be unbearable and you still have all the problems I have already mentioned.

And anyway without any cat I suspect you are gonna run into problems at your next emissions test.

Most cost effective solution without adversely affecting performance / fuel economy is to let the pre-cats die (they won't rattle because of the pressure) and to replace the main cat with a cheapo version from somewhere like the site I mentioned above.

OR go the whole hog, tell stephan at squadra it needs to be remapped to run without a cat, buy the supersprint or CSC and have someone make you up a central decat pipe. But that will cost a grand at least and as I say you are likely to run into big problems come your next emissions test.

 

EB Spares supply CSC catless manifold for £385 +carriage + vat. The picture shows 2 lambda sensors in the pic. CSC and EB Spares and won't supply rubbish which won't work. I have bought CSC from EB Spares for various cars, and can vouch for this. I daresay Kevin or Jason can advise further on what is needed.

A resistor or two for the rear lambda should work. As this sensor should produce a 1 volt flatline waveform, a resistor is exactly what it needs. Failing that, as already stated, Stephan at Squadra Tuning can modify the ECU map to accept this pre-catless setup.

Cloverleaf76 correctly states that knocking out the cat monoliths will adversely affect gasflow even if the term "backpressure" is incorrect. Engine gasflow is an often misunderstood and/or a misquoted subject. The CSC manifold will flow much more efficiently and improve power and torque. Empty cat chambers will also act as echo chambers which will very probably create significantly more noise. The decat section would increase noise slightly as cats do reduce noise even though it is not their function.

A cheap main cat will not flow as efficiently and likely negate any improvements a decat manifold provides. You must keep this cat (at least for emissions testing) but a silencer at other times will work, but not comply with the law. If you were stopped for a roadside emissions check, you'd get a 21/28 day rectification ticket. The green groups have not applied sufficient pressure on the govt to make this an imprisonable offence- yet.

I hope this helps. I don't mean to be pedantic or cause any offence, but this type of advice must be very specific and correct.

 

Hello all,

I've taken a few weeks holiday, so i'm sorry that i didn't chip in to thank those who replied.
In the meantime, i'd like to share with you the latest developments on my cat problem...
thing is... problem's gone, at least for now! <knock on wood>
The car is no longer making that awful noise. I reckon whatever was rattling lose inside the cat got stuck somewhere in the monolith, and basically stopped rattling. The exhaust note is slightly loudlier and higher pitched than it used to, but nothing that you would notice if you weren't looking for it.
I've driven in lousy roads, even some dirt roads, and that didn't make the cat rattle again, so i'm keeping my fingers crossed that it won't anytime soon.

Cheers, and thanks for all your advice.

Pedro

 

Are you sure it just isn't the support bracket for the front pipe/pre cats which is broken?

BTW, I posted a few weeks ago that my brother in law's CF3 156 ran it's big end bearings whilst I was driving rather briskly. Finally, after investigation, it is only no.3 big end shells which have disintegrated- no damage to the crank pins (It's always seems to be no.3 which goes first as they run directly above and close to the exhaust pipe. I think, from memory, no.2&3 big end bearings are both oil fed from no.3 main bearing.)

As the car also needs some exhaust parts, does anyone have experience of fitting a performance manifold and is a lot of ground clearance needed to fit it? (Are axle stands ok?)

Ideally, we'll go for the full manifold. The cheapest I can find is the Supersprint from Motorsport World at £482 inc vat, or the CSC one from EB Spares at £452.38 + carriage.

Failing that, the Supersprint catless front pipe option which retains the manifold is £341 inc vat. This is cheaper than the £385+vat (£452.38) for the standard pre-cat section from EB Spares, and certainly more expensive then the £261 inc vat from cats 4 less. However, I wouldn't go with the cats 4 less option. I know what these cheapo cats are like and I know the issues there can often be fitting them. If someone else is doing it, and you don't mind loosiing a few horses, then fine, but not for me.

After a thorough check, for emissions purposes, I don't think it matters which cat(s) are lost. The pre-cats should heat up quicker than the main cat but I think they are likely to be as efficient at keeping emissions down. Only if all the cats go should there be an MOT problem.

Also, as long as the lambda sensors are good, there should be no issues with engine management lights coming on. The front lambdas are before the pre-cats, and the rear sensor is after the main cat. I think if a management light comes on (after loosing either pre-cats or main cat) it probably indicates a slow switching lambda sensor in the pre-cat section.

 

i fitted a cybox exhaust to my car and got the same rattle as above from the last cat , took a good bit of listening to locate it but that is it . i really hope it just stops soon though fingers crossed . you really have had some good answers from the guys above , talk about going deep into something wow!!!!!!!!!! , very impressive . might just take mine off and see if i can see anything loose maybe .


i had a de cat pipe on my last car , fiat coupe 16v turbo , was a bit too loud . used to back fire when redlined sounded like a race car . when mot time came around put my cat in the boot and ask how much it will be to put it back on for the test and then remove it later , they wanted about 40 pounds for this , which i thought was quite cheap . just means your mot costs about 90 pounds .