Cat or no cat?

Post Fri May 11, 2012 10:37 pm

Quick question - my car currently has a catalytic converter. The new exhaust I plan to fit doesn't. Is it a straight swap? Will it work?
Thanx in advance.....

Post Fri May 11, 2012 11:09 pm

Tried mating up a scorpion backbox (2 piece) off an m40 with cat to my Brother's m40 non cat front end.

connections on the cat section seemed to be different to non cat.

Although that may just be due to it having a non stock backbox.

does real OEM show the flanges?

Post Fri May 11, 2012 11:21 pm

Neil, Ready to fit, I have a non cat front end, and a non cat rear end. The car is currently fitted with a cat at front end and a standard rear. She's blowing from around the cat (i.e.front section). Is it ok to change the full system for a non-cat?

Post Fri May 11, 2012 11:47 pm

And your car is??? and when was it built????

Post Fri May 11, 2012 11:56 pm

Sorry Brian, 1992 316i touring, currently fitted with a cat, but hoping a non-cat system will work? Any advice?

Post Sat May 12, 2012 12:02 am

Get it weighed in, quick!

Post Sat May 12, 2012 12:12 am

What month 1992? If it's after August it will be tested to the later emissions limits at MOT test time, and won't pass, unless you run it on LPG, or have an earlier engine fitted.
Check that the air meter has a CO adjustment pot. on it, probably under a red plug. If you have one, this pot. is currently not connected, as the fuel mixture is currently trimmed by the lambda sensor, but will be needed to adjust idle CO levels to pass an MOT test, even if tested to the earlier limits.
On some of the later cars, when cats had become compulsory, the adjustment pot. was deleted.
If the pot. is present, you will have to remove the bulkhead wiring cover, find a loose white/black wire with a plug on it, find another one with a socket on the end, and plug them together, then get the CO level adjusted on a gas analyser.

Post Sat May 12, 2012 12:26 am

If you want to keep the cat for an easy life, i have a good M40 cat with lambda sat in my shed, available for sale.

Post Mon May 14, 2012 10:07 am

Brianmoooore wrote:What month 1992? If it's after August it will be tested to the later emissions limits at MOT test time, and won't pass, unless you run it on LPG, or have an earlier engine fitted.
Check that the air meter has a CO adjustment pot. on it, probably under a red plug. If you have one, this pot. is currently not connected, as the fuel mixture is currently trimmed by the lambda sensor, but will be needed to adjust idle CO levels to pass an MOT test, even if tested to the earlier limits.
On some of the later cars, when cats had become compulsory, the adjustment pot. was deleted.
If the pot. is present, you will have to remove the bulkhead wiring cover, find a loose white/black wire with a plug on it, find another one with a socket on the end, and plug them together, then get the CO level adjusted on a gas analyser.

Jan 1992. Can you give me a hint as to where the CO adjustment pot would be, if there is one?

Post Mon May 14, 2012 11:11 am

grantfk10 wrote:Jan 1992. Can you give me a hint as to where the CO adjustment pot would be, if there is one?

on the AFM as far as i remember, but playing with it without a gas analyser will screw it up.

i dont notice any perfromnce difference with my cat, only the hair is an issue

Post Mon May 14, 2012 12:44 pm

grantfk10 wrote: Jan 1992. Can you give me a hint as to where the CO adjustment pot would be, if there is one?

I'll get you a pic later if you like?

mrLEE30 wrote:
i dont notice any perfromnce difference with my cat, only the hair is an issue

Took me a while to notice the cat

lol

From a performance point of view, I've just removed the cat on my 318i touring and fitted a 325i exhaust. I kept the M40 downpipes to keep the lambda sensor and grafted the M20 exhaust onto the M40 downpipes. It now revs more freely (i would guess its lost some bottom end torque as a result), but other than that and a slight exhaust note change, I've not noticed much of a difference.

Post Mon May 14, 2012 1:19 pm

jmc330i wrote:
grantfk10 wrote: Jan 1992. Can you give me a hint as to where the CO adjustment pot would be, if there is one?
I'll get you a pic later if you like?

That'd be handy, so I know what I'm looking for

Post Mon May 14, 2012 2:20 pm

Under the red plug I believe. The newer afm doesn't have the adjustment, just a flat blank where it should be....

Post Mon May 14, 2012 11:26 pm

Thanx for that James, mines doesn't have that red plug. Does that mean I can't fit a non-cat exhaust??

Post Tue May 15, 2012 8:04 am

Without the adjustment pot or lambda sensor fitted, the car will not pass the emissions test for MOT. You can either have the lambda fitted to the non-cat downpipes or you should be able to pick up an earlier afm with the CO adjustment and use that - there was a couple for sale on here a while back.