I have a S420 ,MAF failed,and the previous owner drove the car long enough like that,till one of the front cats is almost plugged,will start to lose power after 10-15 miles of driving and showing the o2 and cat code.If I don't need to go thru emission,is it possible to remove all four,or just the front cats and replace them with custom exhaust pipe?,I have a local,inexpensive muffler shop that works well on making custom exhaust that will fit any car.Aside from check engine light,any other issues to expect?

I removed mine no problems for testing I would run e85 2gal e85 with 2 gals. gas. after test fill tank with gasoline

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

You need to a back pressure test first, a clogged cat is usually clogged all the time.

If you do have a clogged cat poking out the affected one would get you going again, just ad a rear O2 sensor fooler plug.

Thanks for the advice,I went yesterday to my local shop,and they installed 2 carefully bent pipes from the front all the way to the resonator,nicely done,for next to nothing because they get about 150$ out of the used converters...anyway,one of the front ones was melted.I had both O2 sensors removed and there is no check engine light on dash,it was on before the job.The computer is not triggering the check engine with the missing converters,how about that?...and the power is amazing,the S420 is flying down the road.

told you,that what happen to my s320 when I got rid of cats,and mufflers.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

So there is no catalytic conversion happening at all and its not throwing codes? Or did you just remove the back cats?

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DS
2010 CL550 - Heaven help me but it's beautiful
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Las Vegas NV

All four cats,front and rear,I was about to install O2 foulers,however,there are no codes,I even plugged the tool and read,there are no pending codes either,car runs just fine,and sound like a Olds rocket engine from the 50's

You need at least the front O2 sensors for things to work properly. The front sensors read exhaust oxygen and the computer adjusts fuel mixture accordingly, the rear sensors look to make sure all the oxygen is used up in the cats. Adding the front sensors is easy, just weld in some threaded bungs, for the rear use the fooler ( resistor ).

With OBD2, you will trip a code, for the moment the car is running in limp mode.

There are only 2 sensors on the s420,between front and rear cats,not 4,one on each side.Limp mode?,this thing is burning the tires right now like a Corvette...

Start at the exhaust manifold and work rearward, the ones that you need are in front of the first cat, they may still be there.

Missing rear ones won't trip a light right away, it takes a while to trip a cat efficiency code.