decat

[mcompact]

Hi guys, i need some help deciding what to do with my exhaust. I have a e46 325ti and want to keep my car as standard as possible and dont want a free flow exhaust. apparently if i decat the car, my consumption will improve and performance will be slightly better.

I have called tnt and they said that the best thing is to remove all 4 cats and put straight pipes in at the manifold and 2 silencer boxes in the center.

Powerpipes have told me that if i remove the cats at the manifold, my car might go into limp mode. He will do it for me but he said that there is a risk that the car could over rev and not perform at its best.

Have any of you guys experienced this limp mode thing and should i put 2 silencer boxes in the center or straight pipes. I done mind a nice sound but it shudnt sound like a citi golf with a free flow.

 

[Spy007]

I did the 318 decat and they put the box in between the 2 sensors. As soon as you remove them you have to put in Cat foolers or you will have issues.

 

[Nastaliq]

Couple of years back, my dad had problems with his catalytic converter.
2003 328i, everyone told him to remove the catalytic converter, as replacing it was something like 15k (cant really remember).

So he had it removed, and regular pipes welded in. Then one day, we are flying on the N2 in Durban at 120 and the car goes into "Limp Home Mode"

(Limp home mode applies to most OBDII model vehicles. Limp home mode generally sets the check engine light and the DME ( BMW ) or PCM simulates the valves of the failed sensor to get you home. This does not apply to all sensors. Some failure will cause a no start situtation that is out of control of the PCM. It is there to serve two purposes, one to allow you to get home or to a repair facility and second, to protect the engine. In some cases it will limit the drivability of the vehicle. The check engine light will go on. )

Car cuts to 20km an hour, dad floored it, engine didnt respond. would only goto 2okm an hour. fortunatley, we were about 10kms from home.

Eventually, dad got a 2nd hand cat from some parts guy and had it fitted. Problem solved.

So, before you do anything with the cats, i suggest getting all the pros and cons, speak to 1/2 specialists.

 

[Sankekur]

I think cat foolers would be the way to go to prevent the car from detecting te lack of cats as an error. Or for it to screw up you fuel consumption.

Would it be possible to fix this error in software, ie using a chip etc? Maybe someone can shed someone with more knowledge can shed some light on this.

...2003 328i, ...

???

 

[ruaangrobler]

I remember reading a post on this very recently on this forum. Someone explained they had issues and found out that the two sesors were put back on wrong way around. Can't remember who, but it might be worth your while doing some searches on this forum for Cats, exhaust etc. There's a lot of good info already around.

Basically, from what I understand (but I'm still an idiot) - take your car to someone who knows what they're doing. If the good people at Powerpipes don't know how to solve the limp mode problem, then they probably aren't the right people for the job. Don't get me wrong, I'm not putting them down - I have a mate with a motorsport 323 e36 and he has powerpipes, and is very happy.

Also, with most Bimmers, your power gains on an exhaust are nothing substantial(this is BMW, they spend gazillions on these kinds of things). Things to think about though is that a full after market exhaust system/decatting can save you a lot of weight and give you better response. I'm seriously contemplating this myself on my 330i. Well, honestly one reason I haven't is because I'm still researching the pros and cons of decatting vs proper full sports exhaust (money being a big part of it, I'm not rich yet :bawling.

As for sound? Well, that's the BIG reason I haven't done it yet. I've heard many BMWs that sound...hollow...for lack of a better word. I really, really like the meaty sound I have, and would like it to be just a little bit more aggressive. Jump on google and youtube or come to a 'meet' where there might be guys who've done it, and talk to them and listen to their cars.

I'm doing the exact same thing now.

 

[Skwinty]

I would think that if you increase air intake (such as increasing supercharger boost), then it makes sense to remove the cats to increase the flow of exhaust gasses.
The cat must restrict the exhaust gas otherwise. :thinker:

 

[msm]

When I spoke to TNT earlier this week (regarding a full system on my 330i), I also asked them about the O2 sensor issue. They said they cater for this (did not ask how though :dunno: ) and their exhaust/headers don't give you any problems with them (with the cats out).

So I agree with ruaangrobler, maybe you should speak to okes with a bit more experience in this area

---

Also, with most Bimmers, your power gains on an exhaust are nothing substantial(this is BMW, they spend gazillions on these kinds of things).

Disagree there bud. One of the major things BMW need to take into account is strict emission control, so this does impact on power gains. However, in SA, we don't have any laws controlling cat removals (yet), so their is some benefit in ditching the factory exhaust & header (which is optimised to control emission rather than outright power).

 

[rick540]

My two cents, and a few points.

I gather from the USA forums that BMW tend to have much larger than normal cats to reduce restriction problems.

The lifespan of a cat is not much over 100000Km, much less here in SA.

My 540i cats died, removed them and the power gain was quite significant. I did not expect this from the above.

Fuel in SA is real sulphur contaminated crap. Every cat equiped car I drive behind stinks of sulphur dioxide. (Rotten egg smell, and a highly toxic gas. Basically the lousy fuel killing the cat by contaminating it with sulphur) Catalytic converters are very clever devices, but are very susceptible to contamination by lead, LRP, silicone, antifreze and any non perfect fuel. I would take a guess that in SA if your car has more than 80000Km on, the odds are your cat is probably past it's usefull life anyway.

LRP kills cats (Only a tank or two of LRP with MMT contaminates the cat with Manganese rendering it useless forever)

Cats cannot be cleaned by taking the car for a hard drive at high speed, this is a total myth. If it's dirty it's dirty forever.

On an OBD II car (post 98) a bad cat will give a check engine light and the owner will probably try to replace a post cat O2 sensor for nothing instead.

You can remove cats on an OBDII car, but you will need an O2 sensor fooler. OBDII cars have a second O2 sensor after the cat that monitors the quality of the gas coming out of the cat to check whether it's working.

Cats can be removed easily on an OBD I car (pre 98 with no check engine light) with no problems.

The only way to tell a blocked cat is to measure the pressure upstream.

Using unleaded without a cat emits more poison into the atmosphere than the old leaded fuel.

I do not like cats at all, it is a concept that has merit in places like California and parts of Europe, here in SA we have too few cars to fully justify their use. I think cats are just a big $ making and window dressing scheme here.

 

[Spy007]

A quick question related to this. If cats are removed what is the recomended Feul to Use. LRP, Unleaded?

 

[rick540]

A quick question related to this. If cats are removed what is the recomended Feul to Use. LRP, Unleaded?

Continue to use unleaded only as the O2 sensors are still in the system and can also be contaminated.

LRP really is only for older cars that cannot use unleaded. On a modern engine with sintered valve seats it really is not nescessary.

 

[mcompact]

would a e36 328i manifold fit on my car? that way i wont have to cut my cats out from my manifold. will this work?

 

[Sankekur]

From what I've seen on the 328, realOEM and the little I could see in my engine bay, it should fit, the bolt spacing seems to be the same.

 

[Rossouw]

Keep your standard set-up but just remove the cats, be careful the cats is laced with a chemical that causes skin irritation etc. After the cats have been removed and the standard pipes refitted you will gain +- 8-10kw and you will have no problem with the cats going into "limp home mode".........just my point of view.

 

[Sankekur]

Its not as simple as that, two of the four cats are in the exhaust manifold branches (on the M54 engine) so to remove them it either requires cutting of the manifold or replacing it.

 

[Epoc]

On the e46 325i that I have. As i understand it there are 4 cats. 2 up front by the manifold and another 2 easily visible by the middle of the under carriage just between the front drivers/passengers and rear seats, correct?

Do you guys know whether there are Lambda sensors at the middle cats (front drivers/passengers and rear seats)?

Thanks

 

[mcompact]

thanks for all your guys help, i have decided to remove only the middle cats for now, later, after i have done proper research will i remove the cats from the manifold or try and find a e36 328i manifold that will hopefully fit.
will let you guys know how my car pulls after i remove the cats.

 

[netercol]

You can remove cats on an OBDII car, but you will need an O2 sensor fooler. OBDII cars have a second O2 sensor after the cat that monitors the quality of the gas coming out of the cat to check whether it's working.

how can this be so difficult to understand guys?

a cat is a restriction and removing it will gain power, end of story. in order to make the ecu think the cat is still there, it has to be fooled into thinking it is still there.

:dunno:

 

[rick540]

I looked at the parts.

What do they do for the manifold cats, looks like a PITA

 

[zaleonardz]

Kill the CAT..... Kill the cat !!!

 

[Sankekur]

The M54 engine's manifold looks like it has cancer when compare the one from the M52