Catalytic Converter failed on 1998 SL280 46k???

[aka$h]

I recently bought my SL and I drove the car this morning to ifnd a rattle from under the car, initially thought nothing of it and thought it might just be because its cold.

The engine warmed up and the noise got worse, so I took it into Kwik-fit (the only people open on a sunday). The guy put it up on the ramp and said, its one of the two CATS and that I should replace both. The wanted £510 each including fitting.

I think its odd that a CAT should fail on a '98 car with just 46k on the clock. Now what do I do next? Reading on the forum, I think ill stop driving it for a while. But I dont really want to spend £1000 on sorting the problem. Any help on this would be very much appriciated.

 

[watsone91]

Are there any elecrical connections coming from either cat

 

[aka$h]

NO, couldnt see any electrical connections.
Cheers

 

[peterchurch]

Then If there are no sensors present (get an MB garage to confirm this!), take the car to a decent mechanic and have the two precats removed. Their purpose is to warm up faster than the main cat to bring the emisions down quicker. You should be able to pass an MOT by running the car up to heat before the MOT.
at worse some tuning work should give the same effect for emmisions

 

[watsone91]

Then If there are no sensors present (get an MB garage to confirm this!), take the car to a decent mechanic and have the two precats removed. Their purpose is to warm up faster than the main cat to bring the emisions down quicker. You should be able to pass an MOT by running the car up to heat before the MOT.
at worse some tuning work should give the same effect for emmisions[/QUOTEThats exactly what i was gonna say peter

 

[aka$h]

Im not quite with you guys. The Cat sounds like its rattling, and once warmed up it gets worse. What would I gain by removing the pre-cats
Cheers

 

[peterchurch]

Thats exactly what i was gonna say peter

Great minds think alike sorry for slipping in and pinching your thunder

aka$h
These cars have three Cats two small (pre cats) at the front and the main one the back of the car they work in conjunction to keep your emmisions down the pre's are small and take little or no time to get up to full efficiency while the engine is cold. Then the main one takes over when it is up to full heat...

Now what is most likely happening with your car is that one of the small pre cats has started to break up (As to where the bits end up is up for disussion! but just to warn you that my MR2 roadster had a VVT engine and that it was well known amongst the drivers that a pre cat failure normaly lead to engine destruction, as a percentage of of the dust would get sucked back into the engine during the lift of the VVT) I am not saying that your SL engine would do the same just that you might not want to drive around with the rattling. The common cure on the MR2 for this problem was for owners to get together and remove the precats before they broke up and took the engine with them.

So if you remove the two precats there will be nothing left to rattle in the exhaust and provided that there are no engine sensors then the effect would be that your car would benifit from increased through flow (more torque ). But the car would need a good warm up just to make sure that is passes the emmisions test for an MOT. In theory you could run your car with no cats and it could still pass an emmisions test it would just need tuning once a year for the MOT

Any help ?

 

[glojo]

So if you remove the two precats there will be nothing left to rattle in the exhaust and provided that there are no engine sensors then the effect would be that your car would benifit from increased through flow (more torque ). But the car would need a good warm up just to make sure that is passes the emmisions test for an MOT. In theory you could run your car with no cats and it could still pass an emmisions test it would just need tuning once a year for the MOT Any help ?

Hi Peter
What excellent advice that will also save a lot of money.

On a side issue, what is your view on low mileage use and the effects it has on the exhaust system? (I am certainly NOT disagreeing with your excellent response, please do NOT even try to justify it)

Its just that some owners think lower annual mileage means less wear, corrosion etc (not parked unused in a heated enviroment) are they correct?

Regards,
John

 

[aka$h]

Thanks for the idea, just trying to think it through,
Statring for the engine, there are 2 down pipes, each one has two small boxes, one which is a cat and one before that. After the 2nd cat the two pipes join and go into the centre box, then the rear box. But it would seem that the noise was coming from the 2nd of the two boxes.
Ive attached a diagram of the exhaust system, im not sure which cat you think I should try to remove.

 

[Dieselman]

Thanks for the idea, just trying to think it through,
Statring for the engine, there are 2 down pipes, each one has two small boxes, one which is a cat and one before that. After the 2nd cat the two pipes join and go into the centre box, then the rear box. But it would seem that the noise was coming from the 2nd of the two boxes.
Ive attached a diagram of the exhaust system, im not sure which cat you think I should try to remove.

As has been said it is probably the small pre-cats. Just remove any that are rattling because they will collapse, block the outlet from their box into the exhaust and then blow back into the engine.

All you need to do is open the exhaust and bash out the honeycomb material.

 

[peterchurch]

I when I had my car MOT'd the guy that was doing the work pointed at the boxes that you have marked as a precat? when he was talking about them so my guess is you have got it right. I would then expect the centre box to house the main cat... now if the rattling is comming from the boxes that are between the centre box and the precats? then it might be that a weld has snaped in the baffle. (in which case nothing to do with the cat at all and the guy in quickfit was talking rubbish)
As a thought, my mate has got an FTO and got a very cheap sports exhaust as part of a deal to prototype it for the guy that was designing them. He is about to get his 3rd one because of a weak weld that keeps popping in the silencer as a result the car farts at about 2.6K revs but no other time

 

[aka$h]

Well I did get under the car and it sounds to me like the CAT is rattling inside, not the precat.
Any way of telling to be certain?
Cheers for all the help guys!

 

[peterchurch]

not really. short of getting it up on a ramp with someone that is impartial. You can still gut the main cat providing there are no engine sensors. at least that will give you some time to think it through

 

[l5foye]

If your car has a full MB history which confirms mileage, I recommend you taking the car back to the original dealer and ask them to check it out. At the same time, sound them out about a goodwill gesture from MB if the Cat has failed. MB reckon a Cat should last at least 90-100k miles. Your's has failed prematurely unless someone has been very careless.

 

[peterchurch]

While I was looking for my car I came across at least 2 other cars that had had them done under 40K miles and the guy that checked my car out, had failed one not much older than mine for the same problem. I would think that MB would say yeah it has only done 46K but the car is 6 years old and thats 3 years out of warranty would be nice if they did do something for you though ...

 

[glojo]

If your car has a full MB history which confirms mileage, I recommend you taking the car back to the original dealer and ask them to check it out. At the same time, sound them out about a goodwill gesture from MB if the Cat has failed. MB reckon a Cat should last at least 90-100k miles. Your's has failed prematurely unless someone has been very careless.

Trouble is normal to 'high mileage' is not as corrosive to exhaust systems compared to vehicles that only travel short journeys or low mileages. Condensation creates rust which in turn corrodes the system from the inside,out.

Regards,
John

 

[aka$h]

Ive been looking at various options today, the cheapest price ive had is £389 each, the other option being a universal CAT but this means a lot of cutting and hassle but would cost around £100 per side.

Does anyone think id have any chance with a goodwill claim, its done 46K with full MB history, its a totally spotless car, not even a stonechip.

Cheers

 

[glojo]

I recently bought my SL and I drove the car this morning to ifnd a rattle from under the car, initially thought nothing of it and thought it might just be because its cold.

First question is, how recent is recent?

If you bought the car and it had a defective 'exhaust' then the chances are better, than if you have owned it for a few months and it just developed.

Were you offered a warranty when you bought the car, and is the item covered?

I suppose the bottom line must be, 'don't ask, don't get'