Catalytic Convertor / MOT Dilemma - E300TD

[MPK]

Need some advice please.
Have a 1999 E300TD with MOT coming up soon.
The only problem it has is a small hole (size of 10p coin) in middle section of exhaust pipe.( Approx 1 ft from CAT, just passed a bend in the pipe).
Also, the CAT has been making a rattling noise for some time now - But - This did not affect last MOT.

Brought car to 3 exhaust garages and recieved conflicting advice from all.
1 - Replace whole exhaust. ( CAT plus rear box) - £700
2 - Replace CAT. £410 ( £350 from EURO CAR PARTS PLUS £60 to fit)
3 - DIY Repair - Jubilee clips and oil / beer can to get thru MOT.

I also phoned local MB dealer - CAT alone £1k plus. And then even more Plus Plus to fit !!

My dilemma is which option to take ?


A - Repair exhaust.Good old jubilee clips and tin jobbie.
- Not sure if todays MOT allows you repair an exhaust in this way ???
- Allows me time to get MOT done and save for CAT. ( Funds low after hols)

B - Replace NEW. Given the CAT rattle is getting worse - Bite bullet now.
- £350 from Euro Car Parts seems reasonable.
( They said its original MB ??? - Irmschaer brand I think they said ??)

C - Replace OLD.Try and find a old CAT from a crashed / scrapped E300TD.
( False economy ?)

D - De-CAT and fit Powerflow type Stainless steel exhaust ?
- Not sure about Pro's / Con,s here.
- Prefer to stick with MB original if costs similar.


Would appreciate any advice,guidance or experiences that you can provide please.

PS - Anyone know where to get a better deal on a new CAT ?

Many thanks Mike.

 

[Dieselman]

You can repair and exhaust. As long as the repair is gas tight it's OK.

The cat isn't needed for the diesel MOT so you could remove it if you want.

You shouldn't leave a rattling cat too long as they can spit back, having said that it's not close coupled on the 300 so probably not a problem.

If cash is tight repair the exhaust for the MOT then look at your options.

Aftermarket cats tend to not be as reliable as OEM ones so can be false economy.

 

[Karl]

I had a similar problem with my 1996 W210 E300D a few months ago.
I went for the cheap option and cut out the Cat and replaced it with a piece of 60mm exhaust pipe and two 60mm clamps.
It passed the MOT with no problems also the car goes better than ever before with no noticeable increase in exhaust noise. On the E300TD, I think the downpipe from the manifold has a bend immediately before the Cat, so it may involve a bit of fabrication unless you can find a pipe with a suitable bend.
Try the Bosal exhaust catalogue for pipes and flex joints.
Good luck.

 

[Thmsshaun]

Go for the DIY job Providing its a gas tight seal you wont have any problems.

 

[MPK]

Repaired exhaust with a tin of Holts Gun Gum and a Holts exhaust bandage.
Easy enought to do - Cost £6.
Sailed thru MOT. ( Extra dose of Millers & BP Ultimate in tank - As always. )

CAT still rattles at tick over.

Considering exhaust options : -

1.MB original CAT - £1000 plus VAT plus Fitting..........................£1350
2 EuroCarParts - £350 plus VAT plus fitting.................................£475.
3.Stainless Steel exhaust - bypass CAT. ( Powerflow ? )...............£400
4.Look for salvage CAT from crashed / stripped E300TD... ............£200
5.Remove - "Gut the cat" - Re-install........................................£100
6.Leave alone - Turn radio up. Cheapest.......................................£0

Any thoughts or expereinces please ?

 

[Copiertech]

maybe the rattle is just the heatshield? does it have a heatshield? decat would be best option, cheap, and improved mpg/bhp.

 

[MainMan]

If the rattle is a broken up cat there is a danger that the bits can be sucked into the bores - don't ask me how because I would have thought the bits would get blown out the back, but that's what the technical boffins say.

I recently had the same problem on a 320 petrol. The cost of the MB part was £1287 fitted (even after deductions for > 3 year old car). I was unwilling to pay this - particularly in the light of the fact that this is the second MB cat failure in 24k miles, so I took the after-market option. I got a cat from autospares (£400) and had it fitted at an independent (£80). All was fine for a week or so until the "check engine" light comes on. The code was "nearside cat insufficient capacity". The people who supplied the cat say I have to return it to them so that they can check if it's faulty manufacture if I want to claim on the guarantee. This is inconvenient and I suspect that they'll just say it's not their problem - just like MB.

These cats are exceedingly complex. There are so-called closed-loop sensors that monitor the various gasses in the exhaust and feed back to the ECU so that it can adjust the mixture (on petrol anyway - don't know about diesel). I'd be interested too know if others have used after-market cats and how they've got on.

 

[SSBB]

cat rattles

I was about to post a message asking for advice about an exhaust rattle I cant cure, when I came across this thread, and I'm glad I did. Looking at the various cost options, I have to say, if you can remove a component and still be legal for MOT's, then why opt for a 'cost' option. I shall be looking to 'bin' my cat as soon as possible. The rattle is certainly in that area.

 

[Copiertech]

I have used aftermarket cats on many vehicles without a problem, maybe the problem that damaged your first 2 cats also took out your aftermarket one. Cats are simple devices, as long as they are not subjected to physical damage or overheated due to unburnt fuel down the exhaust or clogged up with soot they should last until they rust away. the closed loop sensor you refer to is the lambda probe, almost every car since 1994 has one. metal ones tend to last a bit longer than ceramic ones but are a wee bit dearer. still miles cheaper than oem though.

 

[MainMan]

I have used aftermarket cats on many vehicles without a problem, maybe the problem that damaged your first 2 cats also took out your aftermarket one.

I don't think so. When the first cat went I asked the dealer why it had broken up and he said that they'd had a faulty batch. When the second one went - out of warranty - they made little comment, other than to say it needed a new cat and it would cost £1287. I pointed out that cats ought to last more than 8k miles and that it's either a defective part (again) or there's something wrong with the car or the fitting. I couldn't get any goodwill payment out of MB (or any sense) so I got an aftermarket part and went to an independent. He checked the car over and said there was nothing wrong with the engine and that the cat was externally undamaged. The things that can destroy a cat are running rich (though this poisons them rather than breaks them up), a misfire (ditto), physical damage, continual stop start short journeys and rapid changes of temperature such as driving through water. Well, the engine runs fine, the mpg is good, it's undamaged, I don't do short journeys and I haven't driven through water. He reckoned it was almost certainly another defective part.

The new cat is in fact a metal one (for reasons of durability). I had the emissions checked at an MOT station and they're absolutely fine, so I suspect that the cat is working within limits. Unfortunately the limits don't satisfy the various sensors in the SLK. I wonder why.

 

[MainMan]

I have to say, if you can remove a component and still be legal for MOT's, then why opt for a 'cost' option.

Why indeed. It's strange that the government don't apply the same emission criteria to diesels as they do to petrol cars and have absolutely no regulations about particulates. It's different in the USA. That's why there aren't many diesels.

 

[tamrsoft]

I was interested in everyones CAT comments. I was surprised to hear that the MOT doesn't require a CAT on a diesel when testing for emissions.Any further comments on the de-CAT option for diesels, is this the same for the new CDi (common rail models) ? In particular I would be interested to know what you do about the lambda sensor if you opt for the de-CAT (remove the CAT) option and where do you get the bits to complete the exhaust path when removing the CAT.

 

[MainMan]

In particular I would be interested to know what you do about the lambda sensor if you opt for the de-CAT (remove the CAT) option

That's a good question and I'd be interested to know the answer. the way I understand it these closed-loop systems operate by running the engine alternately rich and then lean - lean to build up O2 in the cat to oxidise CO to CO2, and then rich to create CO to reduce the nitrogen oxides to nitrogen. If there's no feedback I don't see how this would work except my remapping the ECU ?????? Or maybe diesels operate differently as they seem to be exempt from emission controls.

 

[tamrsoft]

Have managed to dig up some more info from other forums. I understand that most cars have one lambda sensor before the CAT and this is used purely to monitor the amount of unburned oxygen in the exhaust gases and then adjust the mixture (via the ECU) to balance the fuel/air mix correctly, apparently the CAT is not part of this loop. There are some cars with sensors before and after the CAT and maybe this is the closed loop system you are referring to ? I would imagine removing the CAT in this situation may cause problems. The same article also mentioned that CATs are not necessarily required for the MOT on any car provided the car still meets the legal emission requirements for that type of engine (interesting !!). How true is all this, additional comments anyone ? Great article on Lambda sensors on:

http://www.picotech.com/auto/lambda_sensor.html

 

[MainMan]

That makes sense. If there's only a lamda sensor before the cat you're OK. I think MB (on petrol at least) use one after too as per article below.

https://mbwholesaleparts.com/StarTuned/pdfs/CatConvMar05.pdf

 

[Dieselman]

Closed loop refers to the lamda sensor in front to the Cat.

The engine emmissions are regulated by the ECU and checked and corrected by the lamda sensor....closed loop.

Diesels don't have a lamda sensor because they don't have mixture control as they have no throttle flap in the intake manifold.
All diesel engines run with excess air unless the fuelling has been tampered with.

Petrol engines use 3 way Cats usually made using a ceramic honeycomb for superior performance, diesel Cats are simpler 2 way oxydisation Cats.

The reason for this is that there are generally less polutant gasses from a diesel exhaust so less cleaning up is required.

Someone mentioned that diesels get off lightly at MOT time. Not so. All petrol engines are tested at idle whereas diesels are revved from idle to the rev limiter a maximum of six times.
Many petrol engined vehicles would exibit problems given this treatment.

The two tests are different because the gasses emitted are different, for example petrol engines emit copious quantities of CO (carbon monoxide) whereas a diesel engine will hardly register on the scale for CO.

Removing the Cat from a diesel will make the exhaust smell of diesel and will produce more polutants but not drastically so.
Removing a petrol Cat will have no effect on performance as the engine will still be running over rich to feed the Cat which is no longer there. This is the reason why Cat cars are less powerful than non-Cat cars.

Before removing their diesel Cat can someone please give before and after pressure readings from their exhaust as I am interested in free flowing a diesel exhaust, although I would probably use a larger capacity or even two Cats.

 

[spock500]

Just pulled by exhaust off from the turbo through to the back end.

I can see the cat as the break is very close, looks to be in good condition with no visible damage across the honey comb section (pics t/f)

Dieselmaan, i think you mentioned a while back that the break where mine has gone is quite common, going to pop it into a repair shop for a stainless coupling to be put it, question is the cat?

Do I break it up then weld it or leave alone knowing that's it is quite old and could go anytime?

edit; should have posted on this thread as a continuation

http://www.mbclub.co.uk/forums/engine/18654-kicking-cat-3.html