a few months ago i noticed fibres on the bumper after driving and a rotten egg smell sometimes, does this mean the cat has had it and needs replacing? also if it has had it will it affect power and fuel consumption?

 

sorry don't know if it needs replacing but i do know you will get better fuel consumption and performance if you replace it with a sports cat or better if you remove it altogether, try here ;
http://www.cobrasport.com/exhaust/Su...++94-00/31/0/0

 

Had a very simular thing on my gsi vectra. Turned out to be the battery believe it or not. As above, if it is your cat, don't replace, research and upgrade.

 

yes i know a sports cat would give better flow and increase power but im not sure about fuel consumption, surely if you increase power you loose fuel consumption also if i totally decat the exhaust it wont pass the mot so i need the 1st cat and a sports cat is way too expensive. i really just need to know if i need to replace my standard 1st cat i already have a stainless steel cat back system so 2nd cat has been taken out which is good enough for road use.

 

I've decatted a uk 2000 and my current Sti. After doing both my mpg got a lot better. Up at least 20%.
I'd start speaking to companies that sell exhausts and do mots if you get my drift.

 

a mapped car will be more economical than a standard car when driven off boost due to the fueling being tailored to the exact engine and not a general fit to take into account tollerance.

on boost well be worse lol

 

ideally id like to get it remapped for bhp increase but at the moment cant afford that so just concentrating on passing the mot next month. so nobody knows how to tell if your cats on the way out or had it...? (fibres all over the rear of car after driving and rotten egg smell sometimes) so best thing is to just put in for mot and see what happens and if it fails on emissions or if they tell me the cats gone then act on it. anybody got or know of a used 1st cat for 97 impreza turbo 2000 for sale at a good price?

 

Rotten egg smell is actually from poor combustion because excessive fuel is getting into the exhaust. This fuel causes the catalyts to not work correctly and overheat (hence the smell). The fibres are probably the wadding from the inside of the rear muffler breaking up from the heat (common on nasty aftermarket exhausts).

Usually this is due to overfueling or a misfire, but it can also be a lean misfire.

Fix the fueling/ignition problem first before condeming the cat.

 

it did have a cheap crap exhaust on it untill 2 weeks ago but i put decent 2.5" stainless steal scorpion cat back on it and i dont have fibres on the back of the car anymore but wasnt sure if it was related to the cat or backbox. so what could cause this over fueling or misfire problem? since i bought the car ive done less than 5000 miles and i put new expensive spark plugs, new oil, new oil filter, new fuel filter and decent sus induction kit also replaced the ht leads.

 

if you want to keep it legal i thought £228 was pretty good for a sports cat (do you have any other cat you could put back just for the mot? have been told decating that pipe is a good idea) but a stainless steel cat back and induction kit without a remap? might not pass emissions or be that safe to drive if the fueling is wrong (is it running hot?), so.....a map tweak as it is and hope the cat is ok, then mot and if it fails a new cat then unless you replace like for like another map tweak, or new cat/decat then map once?
would the mot guys do a quick test on just the emissions before the mot to help you decide if you buy them a pint? worth a try..

 

it doesnt run hot, yeah i was thinking of asking my mate a mechanic that works at an mot centre if he can do an emissions test for me so i know if itll pass like it is. when i had the mot done last year there was a hole in the pipe on the old backbox which was also with a decat stainless centre section and it was just off on the emissions, so i had the hole welded and it passed, but since then ive put a new stainless steal backbox on so now its a stainless steal cat back it also had the induction kit when mot was done before so should be ok. im also guna get my mate to check if its misfiring or has a fueling problem maybe he knows what to look for or can hook it up to a laptop but hopefully itll be ok and if i dont have to replace the cat then i wont, i found for a new cat cheapest about £130-£140 but for a sports cat they were much more expensive.

 

i also checked on internet about how to tell if your timing is out and it said: you will notice sounds a little rough on idle, milage will go down a bit, it will backfire and slight change in noise, these things are happening to my car but it only backfires sometimes, as in big pops from the exhaust burning off unused fuel. (what a waste of 99 octane)