Any Known problems with a removed Catalytic converter

[Strap]

Hey all,
Im gonna remove the cat on my e34 525i m50tu , because im starting to get the rotten egg smell after some hard driving, not all the time just if i really jump on it for a couple mins , the muffler shop pointed straight to the cat and said 600.00 usd ,, i think i will spend 20.00 on 2 small straight pipes instead as there is no emissions testing where i am :D , but i want to make sure im not gonna hurt the car? any info would be great ..

Thanks Strap

[BigKriss]

Hey all,
Im gonna remove the cat on my e34 525i m50tu , because im starting to get the rotten egg smell after some hard driving, not all the time just if i really jump on it for a couple mins , the muffler shop pointed straight to the cat and said 600.00 usd ,, i think i will spend 20.00 on 2 small straight pipes instead as there is no emissions testing where i am :D , but i want to make sure im not gonna hurt the car? any info would be great ..

Thanks Strap
no harm done to the car at all. Go for it.

[Rory525]

Please post a result if you do it as Im thinking about it just now.

Would like to know how it sounds and if it performs better...

Thanks
Rory.

[Bill R.]

pollution... the sulfur smell does not indicate that the cat is bad, there are numerous factory service bulletins stating this... the sulfur smell indicates that your running gas with high levels of sulfur, try buying at a better gas station instead.






Hey all,
Im gonna remove the cat on my e34 525i m50tu , because im starting to get the rotten egg smell after some hard driving, not all the time just if i really jump on it for a couple mins , the muffler shop pointed straight to the cat and said 600.00 usd ,, i think i will spend 20.00 on 2 small straight pipes instead as there is no emissions testing where i am :D , but i want to make sure im not gonna hurt the car? any info would be great ..

Thanks Strap

[Strap]

Thanks all and thanks bill r also,
I didnt know about the other items regarding the smell, the gas im getting is rated @ 95 but im stuck in asia so there are only 4 different stations to choose ( brands ) around im using the exxon , as i cant find mobile, sun or shell, .
i think im gonna dump the cat anyway and see if i get a small increase in power.but i will also change fuel this tank before i dump it.
Thanks again Strap

ps: bill , im in asia , not at home in the states. they dont do any emissions or inspection for that matter here. just pay the yearly fee. I would not even consider it if i was home. jersey emmisions sucks.. ;)

[genphreak]

Thanks all and thanks bill r also,
I didnt know about the other items regarding the smell, the gas im getting is rated @ 95 but im stuck in asia so there are only 4 different stations to choose ( brands ) around im using the exxon , as i cant find mobile, sun or shell, .
i think im gonna dump the cat anyway and see if i get a small increase in power.but i will also change fuel this tank before i dump it.
Thanks again StrapIt'll stink like hell without a cat. Any half-serious cop would book the moment they are travelling behind you in the traffic. They'll get you for having a faulty cat let alone no cat at all. I'd only consider it if the cat were bad (read very old). You'll get more power out of a new o2 sensor and other bits I suspect... a new cat is expensive, so if you remove it, make sure you don't wreck it, you might want to put it back...

[BigKriss]

It'll stink like hell without a cat. Any half-serious cop would book the moment they are travelling behind you in the traffic. They'll get you for having a faulty cat let alone no cat at all. I'd only consider it if the cat were bad (read very old). You'll get more power out of a new o2 sensor and other bits I suspect... a new cat is expensive, so if you remove it, make sure you don't wreck it, you might want to put it back...

Does it really smell that bad, what about de-gutting the cat. Since it's rare to do emissions testing in Australia and it has to "look" like you have a cat, could I get away with this?

[genphreak]

Does it really smell that bad, what about de-gutting the cat. Since it's rare to do emissions testing in Australia and it has to "look" like you have a cat, could I get away with this?Most people gut them if they do it (so it's harder to get caught as the fines are HUGE). In Aus our fuel is low-sulfur, however I can't stand rotten egg gas personally, it leaves a bad smell everywhere you go. Imagine droppng the gf off and everyone thinking you or she dropped one as you open the door for her... I mean, its really not very practical for a small gain.

On crumby cars the gain is more, but since Motronic gets things reasonably right I guess the cat is quite finely tuned to the engine. I doubt you will get 10HP gain at WOT, but I am sure someone like Bill or Whit could go a better guess than me...

I'd hazard to say the gain is nil when running part-throttle (ie most of the time), unless you've 'charged your engine and the exhaust has become a serious restriction. :) Nick

[Rory525]

I dont really see why it should smell? Ive been behind cars lots of times with no cats and theres no smell at all.

And I can legally remove mine here , as cars made sometime in either 1992 or 1993 onward had to have them fitted by law.. and once fitted they had to retain them.

Mine is a 1991 car and so its legal to take it off :D

[genphreak]

I dont really see why it should smell? Ive been behind cars lots of times with no cats and theres no smell at all.

And I can legally remove mine here , as cars made sometime in either 1992 or 1993 onward had to have them fitted by law.. and once fitted they had to retain them.

Mine is a 1991 car and so its legal to take it off :DThat's a good point. I'd check the ETK for any differences in cam, injection and ECU on cars built across those dates first though... :) Nick

[Dave M]

Heres my set-up. Its been as such since I bought the machine a number of years ago. I don't condone dropping the cat, and may have replaced mine if it was my decision (PO did it). I don't imagine the replacement section is going anywhere too fast as its constructed out of some 1/4 mile time adding, heavy gauge $hit that will likely outlast the car (god forbid). You can see where they drilled and tapped an O2 home in the crotch.
BTW, there are absolutely no rotten, date ending stenches emitted by the cat-less 5er :)

http://img.photobucket.com/albums/v11/dave_macisaac/Bimmer/Exhaust/Exhaust.jpg

Dave M

[BigKriss]

Heres my set-up. Its been as such since I bought the machine a number of years ago. I don't condone dropping the cat, and may have replaced mine if it was my decision (PO did it). I don't imagine the replacement section is going anywhere too fast as its constructed out of some 1/4 mile time adding, heavy gauge $hit that will likely outlast the car (god forbid). You can see where they drilled and tapped an O2 home in the crotch.
BTW, there are absolutely no rotten, date ending stenches emitted by the cat-less 5er :)

http://img.photobucket.com/albums/v11/dave_macisaac/Bimmer/Exhaust/Exhaust.jpg

Dave M
cool. how did the exhaust note change, if any?

[Omega]

Like Rory525 I'm in the UK and have a '90 525 which can legally be de-catted (It's post '91 cars that have to keep them, bad luck boys :p )

The only question I have about de-catting concerns the Oxygen (lambda?) sensor. I was under the impression that this fed back to the ECU and if it detects emission levels outside of it's parameters (which it would if there is no cat) then it messes with the fuel settings to bring the emissions back into line. Can one of the experts confirm this?

I'd love to de-cat (especially as mine is only held together with weld and hope) but don't want lower mpg or a sluggish engine. At current market levels the cars only worth about £500 so it wont be getting 300-quids worth of new Cat. The prices of larger petrol engined e34's in the UK have dropped due to the rising fuel prices.

[genphreak]

Like Rory525 I'm in the UK and have a '90 525 which can legally be de-catted (It's post '91 cars that have to keep them, bad luck boys :p )

The only question I have about de-catting concerns the Oxygen (lambda?) sensor. I was under the impression that this fed back to the ECU and if it detects emission levels outside of it's parameters (which it would if there is no cat) then it messes with the fuel settings to bring the emissions back into line. Can one of the experts confirm this?

I'd love to de-cat (especially as mine is only held together with weld and hope) but don't want lower mpg or a sluggish engine. At current market levels the cars only worth about £500 so it wont be getting 300-quids worth of new Cat. The prices of larger petrol engined e34's in the UK have dropped due to the rising fuel prices.I'm happy to be corrected on the sulfur dioxide smells... I had a car w/o a cat that did this once and it was awful. Perhaps an e34 is different.. however the o2 sensor is designed to operate in a given temperature range, I'd imagine where they put it near the cat has a certain stability (and it is out of the direct flow in the little y too you'll notice. Be wary of this. I still wouldn't do it myself unless I was modding the engine and it was legal to do so... :) Nick

[High Compression II]

The O2 sensor is generally upstream of the cat on most vehicles--Not sure if it is on the BMW but suspect it should be--so removing the cat will have no effect on the info sent back to the DME

Some systems do have a sensor at the cat, this does send info as to how the cat is working back to the DME--BUT I think this is only in California emission type regions

ANY restriction in exhaust will cause loss of power/extra gas consumption, as you need that wasted power to literally pump the waste exhaust out of the engine, the extra pressure needed places higher loads on the exhaust stroke, --The power needed must come from somewhere..... . Not sure how much 'pumping losses' are with the cat in place, but I reckon if you can legally remove it in your territory, then go for it.--whether you gut your original or replace it with a straight pipe the effect should be the same, maybe slightly better with a gutted cat, as youve then got a larger overall exhaust system volume than with just a straight pipe, The cavity left could act like an expasion vessel for the exhaust on its way down the system.
As a bonus, you may even get a mile or two extra per gallon!

A few years ago, I gutted the cat on a Ford, because it had broken up and was blocking the exhaust. Before removing normally the vehicle would reliably give 34 MPG prior to the fault. After the cat was gutted the fuel consumption fell to 36 MPG--Not much, but it proves theres energy lost in the use of the cat in THAT particular vehicle.....

[Dave M]

I'm happy to be corrected on the sulfur dioxide smells... I had a car w/o a cat that did this once and it was awful. Perhaps an e34 is different.. however the o2 sensor is designed to operate in a given temperature range, I'd imagine where they put it near the cat has a certain stability (and it is out of the direct flow in the little y too you'll notice. Be wary of this. I still wouldn't do it myself unless I was modding the engine and it was legal to do so... :) Nick

The cat-less 91_525im purrs like a kitten, with a slightly louder exhaust note than it's 'cat-ed' brothers. Highway mileage is a consistant 7.9-8.1 L/100km (30+mpg) running 89 octane. No O2 sensor issues.

Dave M

[genphreak]

The O2 sensor is generally upstream of the cat on most vehicles--Not sure if it is on the BMW but suspect it should be--so removing the cat will have no effect on the info sent back to the DME. ANY restriction in exhaust will cause loss of power/extra gas consumption, as you need that wasted power to literally pump the waste exhaust out of the engine, the extra pressure needed places higher loads on the exhaust stroke, --The power needed must come from somewhere..... . Not sure how much 'pumping losses' are with the cat in place, but I reckon if you can legally remove it in your territory, then go for it.--whether you gut your original or replace it with a straight pipe the effect should be the same, maybe slightly better with a gutted cat, as youve then got a larger overall exhaust system volume than with just a straight pipe, The cavity left could act like an expasion vessel for the exhaust on its way down the system. A few years ago, I gutted the cat on a Ford, because it had broken up and was blocking the exhaust. Before removing normally the vehicle would reliably give 34 MPG prior to the fault. After the cat was gutted the fuel consumption fell to 36 MPG--Not much, but it proves theres energy lost in the use of the cat in THAT particular vehicle.....On e34s the sensor is upstream and with early Motronic there was no after or mid cat-mounted sensor.

I don't dispute your experience, however it is a well known fact that a lot of modern cars suffer an economy/power/torque loss when you reduce back-pressure (some cars I hear are even geared differently) as the manufacturer is always seeking to maximise perfromance and economy and may have teaked things in places we don't know. It doesn't mean there are no gains, but what I am saying is that there can be losses too.

My cat was blocked when I bought my e34 535i. It made weird rattling noises and the car ran like a slug. I considered the choices and ended up replacing it with a second hand one from a '91 e32 735i which looked ok. The seachange was amazing. Any car with a blocked cat will run like ****, the same way as one with a blocked muffler would, so peeps be aware that cats don't last forever adn can be easily killed if you run a fumey engine or don't change your O2 sensor; (watch your consumption as a rough but ready indicator).

With the new 2nd-hand $150 cat my car runs really well and when its 3.5L motor is idling around the garage we don't get enveloped in fumes as the cat (if it is hot) is turningalmost all of them into CO2.

I can tell you one thing for sure, I know many catless cars that run on ULP that stink to the high heavens- The 3.5L motor in my mum's Land-Rover for instance (didn't have a cat as in '91 there was a similar rule exempting 4WDs having cats in Australia too). It stunk like a dirty furnace, never really much of a rotten egg smell. For years it just had this filthy, toxic stink that no-one liked and many commented on. I did a lot of work to make sure it was running fine, so it was not a tuning/setup problem.

However re power gains- remember this: Fords and such cars are made to a price. They care little about real performance and longevity except where it directly affects sales, which is the very essence of the reason some smart people buy BMWs. Cats are a very expensive component. To top this BMW cats (and the emission systems designed with them) are much more exotic than others made around the same time. Other manufacturers adopt their technologies after BMW has proven them and this goes for many things but very specifically transmission technologies, traction controls, EFI, ABS, EMSs and, you guessed it, emission controls. A BMW has more than world-leading EFI, engine, suspension, body and emission control system; it has a fantastic cat, so saying you get a benefit on a Ford so therefore you must get a benefit on a BMW is not necessarily true.

You may get some benefit, but at the same time you may not as the whole exhaust has been engeineered as one assembly (and knowing BMW it was engineered with everything else too). It would not have been tacked on in the way we would take it off.

We need to remain cogniscient of the fact that it was one of the greatest challenges BMW had in the late 80s/early 90s; how to implement ULP in cars and NOT suffer power loss (and reduced sales).

It is the principal reason they spent millions introducing one of the most expensive and exotic Engine Management Systems of the day (Motronic) on practically all their models. It was a major engineering excercise, the cost of which was spread over many models after Motronic was developed. It was not just a tack-on to meet regulations as EMSs' were for many manufacturers that followed on recalctrantly making cars that burnt fuel so badly the sulfur was smells were common and burnt cats everywhere.

To rip it out might be a good experiment, but I doubt it will do any wonders (unless you are making a batch of other mods as I said earlier).

One thing I do know for sure, a cat does a lot more than prevent rotten egg gas smothering the car everywhere you go. It catalyses a great deal of the hundreds of other dangerous pollutants as well, so when you have people around with keener noses than we may have, you won't get complaints about how smelly the car is (egg gas or not).

To boot, the cat will cut your emissions so enormously it will help you when:

- you are exposed to the fumes (as we all are quite often I guess) so you don't get cancer so quickly

- help others around you not throw up

So I reckon, since it is there, if it works take advantage of it. Platinum is expensive stuff and the laws preventing you de-cat your cars are even there for a reason... Having said all this, if one had a early nineties Ford or GM, I'd understand this desire to remove the thing, many of them are awfully implemented. :) Nick

[Strap]

Oh No ,
Now im torn as what i should do , Of course i dont want to add any dangers to other people in regards to bad or harmful smells , i also want to get my 5 er running back to top perfomance and it seems the cat is causing some problems as the second shop i took it to ( today) said the cat was on its way out, this shop only wanted 725$ usd to replace it ( and they had one there ) but i did replace the o2 sensor and fuel filter to see if any changes are noticed. if no change then i still want to dump the cat as i got the E.A.T chip on the way ( thanks mark for international shipping ) the rear muffler i changed already and for the sound guys out there it does sound real deep toned at idle and great at @ 3500 rpms ( sounds like v8 ) i will post the brand and model number later for the muffler if anyone wants it , anyway right now i will wait a week to see whats up and take it from there.
Thanks all
Strap

[genphreak]

Oh No ,
Now im torn as what i should do , Of course i dont want to add any dangers to other people in regards to bad or harmful smells , i also want to get my 5 er running back to top perfomance and it seems the cat is causing some problems as the second shop i took it to ( today) said the cat was on its way out, this shop only wanted 725$ usd to replace it ( and they had one there ) but i did replace the o2 sensor and fuel filter to see if any changes are noticed. if no change then i still want to dump the cat as i got the E.A.T chip on the way ( thanks mark for international shipping ) the rear muffler i changed already and for the sound guys out there it does sound real deep toned at idle and great at @ 3500 rpms ( sounds like v8 ) i will post the brand and model number later for the muffler if anyone wants it , anyway right now i will wait a week to see whats up and take it from there.
Thanks all
StrapWe all want to know about good muffler options... if the cats are toast then there's not much harm to be done gutting them, but its hardly easy which is why most peeps splice in some pipe. You can always do what I did and get a new 2nd hand one that looks good, they aren't hard to change if you have some ramps and a 10mm socket, extension bar or two and a ratchet... just make sure you get all the right seals before you start the job (you will need at least 8 new copper M10 nuts too, all can be got reasonably cheap from the dealer).

I just used the time I had (as mine still ran well enough) to find a good one going cheap. btw, one good way to tell is if the cat is bad is if it is running really hot (making you hot inside the car) or rattles at some point, ie when the engine is under various loads. Other's might know of other symptoms other than general sluggishness....

[SRR2]

Known problems? If you're in the US, yeah, there's a problem. It's not legal, and it's not responsible. You could get into real trouble (read $$ fine) if you get caught with a modified emissions system. Hell, I'd happily turn you in myself. There's no excuse for anyone deliberately causing more pollution.

[Dave M]

Known problems? If you're in the US, yeah, there's a problem. It's not legal, and it's not responsible. You could get into real trouble (read $$ fine) if you get caught with a modified emissions system. Hell, I'd happily turn you in myself. There's no excuse for anyone deliberately causing more pollution.

Well then, I better not drive my e34 through the US, or fly in a plane, or mow my lawn, or take my snowmobile or 2-stroke quad to work, or go fishing in a powerboat, or purchase goods transported long distances by Walmart to save a penny or...........

They should all be made illegal :)

Dave M

[iainand]

i de-cated my 1993 diesel 525, its not a legal requirement for a diesel to have a cat in the UK, and at the annual MOT my car was kicking out way less pollution than many 3 year old so called more sophisticated modern diesel cars. So yes i would agree with an earlier post that BMW emmisions systems are way ahead of their time.

In my opinion i have found cats not to be so fragile as they are made out to be, my previous car had a cat that had a hard life, and would still pass emmision test every year. At last test car had done 160,000 miles on same cat, 10 years old, it had a few knocks on the casing from speed bumps etc, 2 head gaskets blow on engine and god know what go through cat, then blew the engine completly and drive a further 30 miles after that, cat still performed!!

[High Compression II]

Known problems? If you're in the US, yeah, there's a problem. It's not legal, and it's not responsible. You could get into real trouble (read $$ fine) if you get caught with a modified emissions system. Hell, I'd happily turn you in myself. There's no excuse for anyone deliberately causing more pollution.


Well, Personally I havent burned more than say 10 gallons of Fossil fuel in any vehicle Ive owned for the past 6 years or so--The only fossil fuel Ive used, has been the contents of the vehicle tank when purchased, and the addition of small quantities of RUG in cold weather...........

Carbon trading anyone?--Who wants my share?! (Sure must have saved several hundred tons of CO2 emissions over the years, BioDiesel and Veggy oil are C02 Neutral..........!)

Big companies do it all the time here in the UK, for financial gains of course!