How to replace R/H catalytic converter - Part 1

[Kobus]

My E320 has developed the notorious CAT rattle – of course just out of all warranties at 83,000 miles. Quotes to replace a single cat varied from $1,000 to $1,500. So I’ve decide to tackle it myself, instead of forking out all that green stuff to the dealer/exhaust shops. I’ve taken some pictures, since I think that more people will be coming into the situation where they are no longer cover by any warranty. The job took me about 2 hours.

The first step is to diagnose which side is bad. Not such an easy task as it may seem, since the 2 pipes runs just a few inches from each other and makes it hard to pinpoint the bad one. For this I used the highly complicated and technically advanced Catalytic Converter Diagnostic Device (CCDD) (Local and International patents pending) - Photo 1

Just press the one end to your ear and the other end to the cat while the car is idling in the condition where the cats rattle – in my case the car had to be in gear, so be careful!. For a second opinion, I’ve had my son listen afterwards, while I pressed the end to the cats out of his sight and we came to an agreement on the bad side. (Well, it also helped that the left side had a manufacture date of 10/2005 and was probably replaced by the previous owner ). I would suggest that you at least have metal on one end of the hose , since those cats get extremely HOT.

The dealer wanted $850 plus for the right-hand cat, so I decided to try a non-OEM one at $595. The replacement cat has a 5 year/50,000 mile warranty. Non-California owners may have more options and can maybe elect to just to cut out the bad cat and have a replacement welded in.

The following are the tools needed for the job (photo 2) :

12 mm socket
13 mm socket
12 mm spanner
13 mm spanner
Ratchet
O2 sensor socket
Some very long extensions (12 inch plus)
Torque Wrench (Optional)

VERY GOOD STANDS OR RAMPS!!!!

You will be spending a lot of time totally underneath the car, and you are going to push and pull quite bit, so your setup MUST be VERY stable. Don’t try to skimp here – you may end up injuring or killing yourself.

[Kobus]

Start off by unplugging the 2 O2 sensors at the places as indicated in the next 2 photos. One is inside the engine compartment and the other one is underneath the car. They are a very tight fit, with a small protrusion to hold them, so they require quite a pull. It also helps to have a small screwdriver to lift the plastic lip over the protrusion.

[Kobus]

Lift the car up at least on the side you are going to replace the cat. Next loosen the 2 collars mating the cat portion to the rear part of the exhaust system. This is the point where you need a 13 mm socket and both a 12 mm spanner and 13 mm spanner. The collar on the non-replaced side had bolts with 13 mm heads and 12 mm nuts! The collar on the left side had 13 mm bolts and nuts. All nuts however looked the same, so maybe this was an upgrade on replacement. (Photo 1)


Also remove the brace between the 2 cats, using a 13mm socket. (Photo 2)

[Kobus]

Next take your long extension and remove the 2 bolts holding the cat against the manifold. (Photo 1) The one closest to the engine is the easiest to reach, so first loosen that one. Just make sure that you keep your head here. Since you are working upside down, it is easy to confuse which way is loose and which way is tight – and you surely don’t want to take it in to have a broken bolt drilled out. Since the collars are loose around the pipe, it will tilt over and make the second one easier to remove. The second one (not visible in the photo) is where I ran into a bit of a problem. I did not have the long extension that I show in my picture, so I used a 13 mm spanner with a swivel box head. The space is so limited that you cannot turn the bolt more that 1/8 of a turn, so it took a lot of small turns to loosen it. Even with a long extension it may still be a problem, since the sway bar mounting is just off line with a straight line to the bolt. To make it worse, the sway bar mounting has a little shield on top further impeding the line to the nut. Next time I’ll probably try to remove the shield, or just bend it out of the way.

Once you have loosened both bolts, you can remove them totally, since the cat is still supported by this front hanger (Photo 2) You will again need both a 12 mm socket and a 13 mm socket. The front nut is 13 mm and the back one is 12 mm. On the replaced left side they are both 13 mm, so I guess it was standardized on replacement. The cat will now be free and you can wiggle it forward to pull it out of the exhaust pipe. The space is quite tight, but you will be able to move it enough to the front to pull the pipe out. Be careful not to damage the O2 sensors when you pull the cat out. In my case the cat pipe pulled out quite easily from the exhaust pipe.

[Kobus]

Now is the time where you can found out if your diagnosis was correct. Shake the cat or turn it over end to end and hopefully you will hear the plate fall around inside. Otherwise go and have a few beers before continuing. In my case I was correct and it was the rear-most cat on the right side that was bad.

Photo 1 is a shot of the old and the new cats. Besides the physical shape of the rear cat, the flex point is different (concertina on old - photo 2, braided metal on new - Photo 3). A bigger difference is in the collar. The old one had a ceramic collar, while the new one has a metal collar (Photo 1). The new collar is also only half the thickness of the old one, so you’ll need some washers under the bolt or you’ll have to cut the bolt. If you don’t the bolt closest to the engine will turn into the manifold. I just used an old nut as a spacer under the bolt head. Also make sure that you get a new seal, especially if you are doing the right-hand cat. It is made of some metallic-plastic material, and my old one was dripping water when the engine was cold. Also note that there is no gasket between the manifold and the cat pipe.

Remove the old O2 sensors from the old cat (photo 4) and coat them with an anti-seize lubricant (photo 5) before installing them on the new cat. Make sure that you note which one is in front and which one is in the rear, since they are not interchangeable. Hint – the one with the long wire goes in the front.

Now I know a lot of people say you should also replace the sensors when you replace the cat. I did not do it, since mine still give perfect readings. Also the ones on the right-hand side can easily be replaced even with the cat fitted to the car. So I’ve saved myself more than $300 dollars on this alone.

Also remove the rear collar from the old cat and slide it onto the new cat. Next slide the new gasket onto the pipe (Photo 6). Also remove the hanger bolts from the old cat and insert them into the hanger mounting on the new cat.

[Kobus]

Fitting the cat is exactly the reverse of the removal. Maneuver the front of the cat over the swaybar and push the rear end of the cat pipe into the exhaust pipe. Getting the pipe in deep enough is the hardest part of the job. Do yourself a favor and get two 4 or 5-inch long bolts and nuts of about a ¼ or 3/8 inch diameter. Use these to pull the pipe in by putting them through the collar and tightening them until the collars are pulled close enough to use the real bolts. Don’t tighten the bolts totally – just get the collars close enough to so that you can use the correct bolts.
Now proceed to tighten the bolts, while you continuously check if you can fit the front collar to the manifold and/or the bolts in the front hanger. Don’t fully tighten any thing at this stage, just get all the bolts to take. I inserted the bolt closest to the engine first. It’s the easiest one, so that why I did it first. Just tighten it 2 or 3 turns and then do the other bolt. You may have to do some pushing/pulling to get the alignment correct. Once the second bolt has taken, you can start tightening both bolts. Only finger-tight both bolts, since you may still want to do some final alignment.

Check your exhaust alignment and make sure that there is enough clearance everywhere. Tighten the cat to manifold bolts, alternating between the 2. Tighten the bolts on the cat to exhaust collar fully. Tighten the front hanger fully. Replace the brace between the two cats.

Plug back the O2 sensor wires. Note that the plug is keyed, so it can only go in one way.

That’s it. All done as can be seen in photo.

I've also had a look at the righthand cat, and that seems to be even easier. The cat and exhaust pipe is just a face-to-face fit with a gasket between them, so there is no pipe to slide out or in.

[cerritos]

Originally Posted by Kobus

Just press the one end to your ear and the other end to the cat while the car is idling in the condition where the cats rattle – in my case the car had to be in gear, so be careful!. For a second opinion, I’ve had my son listen afterwards, while I pressed the end to the cats out of his sight and we came to an agreement on the bad side. (Well, it also helped that the left side had a manufacture date of 10/2005 and was probably replaced by the previous owner ). I would suggest that you at least have metal on one end of the hose , since those cats get extremely HOT.

This is a very innovative method to diagnose a car problem. It reminded me of how the doctors listen to our heart and lung when we're sick.

[skipinschool]

I could admit.... this is a pretty difficult task... Ive done it myself 1 1/2 times (taking a CAT system off one junk E-class... then taking the one out of mine and putting the other in.)

It was a pain in the azz, but got it done in about 1 1/2 hrs...
now I gotta replace it agian!! sounds like the "rock tumbling" noise

[cerritos]

Great DIY writeup!! Great pictures too!!
We all appreciate your excellent work. Thumbs up!!

[ohlord]

They are available for left ,right ,front, back for $ 50 or so each,oem match,new universal O2 $65 each you splice in the cats if you weld or have a muffler shop do it,you splice the connectors of the old O2 to the univ O2( bosch oem).$ 460 in parts another $100-$125 labor at the muffler shop if you can't weld. $560 ish both sides new and new O2's to boot.
As to the O2 sensors they are a 100,000 mile maint issue,so replace them if the cat failed,your down there anyway and if your near 100,000 i.e. 85,000 up your getting close.
ohlord
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