To Cat or DE-cat?

[Catman]

I have a left-hand drive 1987 300SE (W126).
It is fitted with a catalytic converter, which has started to break up. The price of the stealership cat is exhorbitant, but I cannot find a UK distributor with an aftermarket cat for this model. Ideally, I would like to de-cat this car - but I get virtually no help from Mercedes stealerships. I have had some help from Andy, but I need more information. Has anyone de-catted this car? If so, what is involved (re. the lambda sensor, etc).
Thank you in anticipation.

 

[Tilly]

I'm not all that up on my mercs as I'm new here but there shouldn't be any problem with simply having a bypass section welded in, as far as im aware it cause any problems apart from it will reduce backpressure, is there a pre and post cat lambda sensor or just the one?

 

[Catman]

Tilly - thanks for your reply,
There is just a pre-cat lambda sensor. I can obtain a non-cat front end, but it is what to do with the lambda that is my concern. Apparently I would need a coded plug which affects the engine ignition timing, then I can remove the lambda sensor. If this is all I need to do, I just need the part number of this plug. The stealership are not all that interested, they simply want to replace like for like - but at £1,500 to fit a Merc. cat ........... I don't think so.

 

[Tilly]

personally I'd remove the cat and replace it with a straight through section and then have a remap. Reason being you'll increase power but lose torque by removing the cat. But the remap will regain that torque, make the car overall nicer to drive and also solve any fueling problems caused by the altered exhaust pressures from the lambda sensor meaning you can happily leave it in. Would cost a few hundred yes, but at the same time you're seeing the benefits of a smoother driving car, a quicker car, no cat to go wrong in the future and an easy way to p*ss tailgaters off play with the throttle and watch the headlights behind you slowly fade into the distance and the exhaust burns their front bumper lol

 

[big x]

Remove the cat and bash out the substrate with a long rod.Easy to do as the honeycombe has little strength.
I don't understand why people say the back pressure changes with or without a cat as the rear silencer is the most restrictive part of the exhaust and a cat has the same cross sectional diameter as the exhaust down pipe because it's wider.

adam

 

[Tilly]

because its like any form of filter in the way it restricts flow, if something is blocking somethings path it will be slowed down, if its exhaust gasses are slowed down upon entry of the cat, build up of the gasses will cause higher pressure while its forcing its way through the honeycombe structure, hence cars backing up and popping when you back off the throttle with a decat section fitted because there are no restrictions. Backboxes and middleboxes may be restrictive yes, but not is the same sense as a cat, they're a lot free-er flowing because they dont have the same tight honeycombe structure in the gasses path, they only expand the surface area and muffle the sound, obviously they do aid in pressure but not in the same way as a cat. Its more noticeable on smaller engines but the instant the cars cat is removed, if you put your foot down, it doesnt go as well as it would with the cat in place until you hit the top end

 

[Parrot of Doom]

TVR owners (I had a TVR before my W210) would regularly de-cat their cars, lots of people would install a small cone in the manifold where the 2 banks met (V8 engine) to improve the flow of gasses.

Personally I'd just cut the cat out, poke it out with a big stick (WEAR A MASK WHEN YOU DO THIS), and weld it back in. Dunno about the lambda sensors though.

 

[tamrsoft]

De-CAT sounds an interesting idea, big question I would ask is how much it affects emissions making it a possible MOT failure risk. Has anyone comparative emission figures before and after CAT removal.

 

[Tilly]

removing a cat will immediately fail the mot on any car registered after august '92 (J reg) The easiest way round it is to cut the old cat out and modify it, a little bit of welding here and there and you can fit a flange on either side allowing it to simply bolt on as and when required, four bolts and away you go. This isnt off a merc but it give s you an idea of what to do with the cat/decat pipes:

 

[big x]

I have a 97 C-180 and have tested the car with and without cat and it is marginally quicker 30-70 mph without.In all other respects it runs the same no popping etc.The gearbox changes at the same point etc. I have a cheap aftermarket cat that rasps and sounds noisy (perhaps because it's case is made of thin gauge stainless steel while the original is some sort of thick aluminium coated steel) so I only use it to get through the MOT at other times I put the gutted Eberspacher back on.The difference in torque is so marginal I can't feel any differences although I accept the automatic gearbox may mask it at low rpm.
I was looking at some flow figures for a Lexus Soarer V8 and the twin cats are not really restrictive,the big loss is in the poor manifold design.Change that and you get 15 BHP.Take the cats off a 1991 Soarer and you get nothing worthwhile.

adam

because its like any form of filter in the way it restricts flow, if something is blocking somethings path it will be slowed down, if its exhaust gasses are slowed down upon entry of the cat, build up of the gasses will cause higher pressure while its forcing its way through the honeycombe structure, hence cars backing up and popping when you back off the throttle with a decat section fitted because there are no restrictions. Backboxes and middleboxes may be restrictive yes, but not is the same sense as a cat, they're a lot free-er flowing because they dont have the same tight honeycombe structure in the gasses path, they only expand the surface area and muffle the sound, obviously they do aid in pressure but not in the same way as a cat. Its more noticeable on smaller engines but the instant the cars cat is removed, if you put your foot down, it doesnt go as well as it would with the cat in place until you hit the top end

 

[starvo]

Numerous fault at once

I own a MB c200 1995. i wonder if anyone out there have had similar problems as i am going through at the moment. My dashboard and heating control back lights flashes and i loose control of the controllers, when that is happening the heating system will be constantly hot. This problem is on and off. I have had the controller console replaced by that did not cure the problem.

A week ago, I was told by a machanic that the alternator needed changing, after replacing the alternator the car have developed more problems.A day after he replaced the alternator, the car could not start without a jump , so i took it back , the guy sold me another battery but this l did not cure the starting problem.

I managed to start with a jump start, but the battery did not charge up infact it seemed to be loosing more power as i was driving eventually it lost all the power that the in stereo and inside lights just switched off on theri own. I had to call breakdown services. The car was toured to the same gararge and the breakdown services guy told me i have an electrical fault and my cat needed replacing. Is it normal for a cat to blow all of a sudden, can a cat cause the drain on the battery.

Is it a combination of problems i am having ? whow best and economically can i sort out the problems please help

 

[starvo]

I own a MB c200 1995. i wonder if anyone out there have had similar problems as i am going through at the moment. My dashboard and heating control back lights flashes and i loose control of the controllers, when that is happening the heating system will be constantly hot. This problem is on and off. I have had the controller console replaced by that did not cure the problem.

A week ago, I was told by a machanic that the alternator needed changing, after replacing the alternator the car have developed more problems.A day after he replaced the alternator, the car could not start without a jump , so i took it back , the guy sold me another battery but this l did not cure the starting problem.

I managed to start with a jump start, but the battery did not charge up infact it seemed to be loosing more power as i was driving eventually it lost all the power that the in stereo and inside lights just switched off on theri own. I had to call breakdown services. The car was toured to the same gararge and the breakdown services guy told me i have an electrical fault and my cat needed replacing. Is it normal for a cat to blow all of a sudden, can a cat cause the drain on the battery.

Is it a combination of problems i am having ? whow best and economically can i sort out the problems please help

 

[KLP 92]

You might have more luck with a response if you place your question as a new topic in the engine section.

 

[Ian B Walker]

I own a MB c200 1995. i wonder if anyone out there have had similar problems as i am going through at the moment. My dashboard and heating control back lights flashes and i loose control of the controllers, when that is happening the heating system will be constantly hot. This problem is on and off. I have had the controller console replaced by that did not cure the problem.

A week ago, I was told by a machanic that the alternator needed changing, after replacing the alternator the car have developed more problems.A day after he replaced the alternator, the car could not start without a jump , so i took it back , the guy sold me another battery but this l did not cure the starting problem.

I managed to start with a jump start, but the battery did not charge up infact it seemed to be loosing more power as i was driving eventually it lost all the power that the in stereo and inside lights just switched off on theri own. I had to call breakdown services. The car was toured to the same gararge and the breakdown services guy told me i have an electrical fault and my cat needed replacing. Is it normal for a cat to blow all of a sudden, can a cat cause the drain on the battery.

Is it a combination of problems i am having ? whow best and economically can i sort out the problems please help

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