R 129 500SL 1990 De-cat

[gfern]

Does anyone know anything about permanently removing the catalytic converter from above car. What is involved and what are the complications ?.

 

[Spike]

LOL... welcome to this weeks hottest debate

Try http://forums.mercedesclub.org.uk/showthread.php?t=9707

 

[peterchurch]

Yes,
if you want to do this I would suggest that you talk to a company called Heyward and Scott in essex they will build you a custom exaust removing all the pesky bits in between...

They offered to build me the front section for about £400 but could be cheaper than that there is a company that will do this in Birmingham as well.

Now the downside...

If you do it then you will need to retune the engine and maybe reprogram the ECU. If you don't the car could attempt to run on a very lean fuel mixture. This in turn can lead to holes in the pistons and early death of the engine

I was thinking about doing this on my car following the failure of one of the cats last week. But I decided that risking my engine was not worth it when I can get a decent cat for £300

Best regards,

Peter

 

[190]

The easiest and less expensive way to remove the cat is to remove the section of exhaust that houses the cat and push a metal rod into the cat to enable you to break the ceramic out of the cat box, it should brake very easily just make sure all the ceramics is removed and then refit to car. job done. Its not rocket science but it does work and your wallet stays healthy

 

[190]

Yes,
if you want to do this I would suggest that you talk to a company called Heyward and Scott in essex they will build you a custom exaust removing all the pesky bits in between...

They offered to build me the front section for about £400 but could be cheaper than that there is a company that will do this in Birmingham as well.

Now the downside...

If you do it then you will need to retune the engine and maybe reprogram the ECU. If you don't the car could attempt to run on a very lean fuel mixture. This in turn can lead to holes in the pistons and early death of the engine

I was thinking about doing this on my car following the failure of one of the cats last week. But I decided that risking my engine was not worth it when I can get a decent cat for £300

Best regards,

Peter

Peter that is the reason for the lambda censor being fitted. Is to monitor the exhaust gases and get the required burn mixture so as not to damage the cat. There is no difference to the cars running with the cat removed. The only downside is the MOT If your car was registered after Aug 1992 [K-REG]

 

[peterchurch]

Peter that is the reason for the lambda censor being fitted. Is to monitor the exhaust gases and get the required burn mixture so as not to damage the cat. There is no difference to the cars running with the cat removed. The only downside is the MOT If your car was registered after Aug 1992 [K-REG]

Yes but the SL has two precats (1 per bank) then a pair of cats (again 1 per bank) they run into a middle box and then into the silencer. There are lamda sensors up and down stream of each of the cats. These montior the flow of the gases each downstream lamda must register a lower level than its upstream counterpart these two levels are then used to calculate the fuel mixture for the engine. This is why the SL requires the extra work. I agree that poking the buggers out will sort of work. But the tuning/ ECU modification will still need to be done in order to stop the ECU registering cat failures. It can also send the car into a self protection mode, at which point, the car starts to limp like someone punched it in the ribs I think that there may also be some maths to do with the changes in exhaust gasflow as you will have opened the flow of the exhaust by removing the monolyth while leaving he wider tincan that was put there to smooth out the build up of pressure caused by the monolyths presence (if you get my meaning)

 

[190]

Agree with you, I have never removed the cat on these cars but have done so on many others without any problems. All the cars ran the exact same with the cats removed but then again they only had 1 cat and 1 lambda sensor

 

[peterchurch]

The underside of the SL is something to behold I really would not want to replace a complete exhaust end to end with the MB parts

I think the best route is to get the complete exhaust off, and replaced with a custom job, before any of it fails then replace the exhaust and Flash the Ecu once a year for the MOT...

Regards,

Peter

 

[peterchurch]

Hi,
I thought I had better post an update. I have just been under the car to fit my new cat, and found that I ony have one lamda sensor per bank. That said the exhaust still has a hole to connect downstream sensors so it would be best to check what you have before you start altough one having only one sensor will mean that 190s statment about just booting the cats out alot easier and probably true

My car is now sitting on my mates service bay waiting for a second cat pipe to turn up. I have fitted a Timax Steel replacement on the drivers side. The monolyth is made of stainless Steel as opposed to the normal ceramic type. The whole pipe (two cats) cost £327 +plus vat fitted vs £512 plus vat for a Ceramic MB part unfitted...

Given that the company I bought this one from, now owns the company that make the Mercedes exhausts and supply the exhaust for the New SLK and the ML series I am quite happy that there is no degradation in quality

I am replacing the other side so that the presures will be the same on both sides of the engine. Timax said this did not need to be done but I might as well get them done together

Best regards,

Peter

 

[gfern]

Thanks for advice so far,it would seem that it should not be that difficult particularly for pre 1993 cars. We don't have the MOT system here in Ireland and the rules are for vehicles registered from 1986 to Dec 1993 Carbon Monoxide content that is < 3.5% and Hyrdocarbon content < 750 ppm both measured at idling will pass the test. Does anyone have any experience of achieving these results after removing the cat or (cats) and did it affect the readings to the ECU for mixture control etc. I like the advice from 190 which matches my engineering skill perfectly but am still a bit concerned especially where readings to the cars brain are concerned. So any more info would be appreciated

 

[R129]

For the first few months of R129 production they were available without a cat, I know I have a September 1989 built 500SL. When in good order this runs at a steady 1.5% co and the HC output is around 200 ppm which is not bad for 120k miles. Your car will likely produce lower figures as the cat equipped cars run leaner and should fall well within the figures you give.

Don't expect much in the way of power or mpg improvements as the car is still adapting the mixture as though it has a cat whereby the pre cat model had a different ignition and fuelling map which gave 333bhp and about a 5% improvement in MPG.

The ignition map on early cars can be altered by changing the trimming plug on the ignition module but in order to get the revised fuelling map you would need an early injection ecu which aren't exactly common!
If your legislation allows I personally would go down the poking out the innards route and leaving everything else in place. Not popular with enviromentalists but a lot cheaper than a pair of replacemants.

 

[gfern]

R129 thanks for that it helps resolve the issue a bit more for me I wonder if it is possible to reprogram the ECU or chip it. My car is a 1990 500 so missed out on the pre cat, just out of interest what sort of mpg do you get. My overall average is 16.60 mpg with 24 being possible on a decent run.

 

[R129]

Have run the car as a daily driver but now I have it on a 3000 mile classic policy. In the 3 years I've had it I would say it averaged about 20 mpg.
Still amazed at how reliable these early 129's are given the very early technology employed in them, for example BMW didn't start variable valve timing on their V8's until 1998 and then they still proved unreliable.
Enjoy the Summer when it arrives.

 

[peterchurch]

I have a set of cat pipes that I have taken off my 99 three of the cats are fine just the drivers side rear one has blown (it can be rebuilt for £200)

These would make a good set to decat as a tester or you could rebuild the one failed one and have a full set

Anyone interested ??