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post #21 of 43 (permalink) Old 01-28-2018, 03:57 AM
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So I watched a video on measuring temperatures pre and post catalytic converters, so I decided to try this.

Left cat: pre- 220, post - 260
Right cat: pre - 260, post - 130

Because of the cooler temp after the right cat, it’s supposed to indicate the right cat is clogged.

Any thoughts?
as an amateur mechanic i would replace the cat(s) after measuring what you measured IF there is rattling when you hit the cat like illstplaya suggested (see above).
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post #22 of 43 (permalink) Old 01-28-2018, 05:23 PM
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If you dont live in a state where emissions is an issue and you have a sawzal i would cut one the cat off that has off temps and drive it to see if the car runs normally.

The secondary cats are used for emissions and do not mess with the cars ecu but they are the cats that get clogged. To be honest if you live somewhere that isnt strict about emissions i would cut them off and weld a pipe. The car will get a performance increase and better fuel mileage not to mention save you from clogged cat headaches
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post #23 of 43 (permalink) Old 01-29-2018, 06:16 AM
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The secondary cats are used for emissions and do not mess with the cars ecu but they are the cats that get clogged. To be honest if you live somewhere that isnt strict about emissions i would cut them off and weld a pipe.
This question will show my ignorance regarding the v8s, but what exactly is a "secondary cat" and why do you say they "mess with the cars ecu"?

I know only the v12 engine. Mercedes, to my knowledge, uses the abbreviation TWC (three-way converter) for the whole line-up of w140, and the three-way means:
1. The converter oxidizes CO to CO2
2. The converter reduces NOx to N2
3. The converter oxidizes unburned hydrocrabons to CO2

The converter, again only based on my limited knowledge on the v12 set-up, cannot mess with ECUs.

Did you mean O2-sensors (aka lambda-sensors). They are the only component near the TWC that provides input to the fueling computer(s).

Please clarify.

Steve

PS Cats will "light up" at about 250 (I assume this was in Celsius), but the normal operating temperature will be much higher, probably in the range 600-800C. To the OP -- did you warm up the car or it wasn't possible because of the backfire? If that's the case, a more conclusive test will be to measure the exhaust back-pressure during the first 2-3 minutes of operation

Last edited by Steve_B; 02-17-2018 at 06:12 AM.
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post #24 of 43 (permalink) Old 01-29-2018, 02:18 PM Thread Starter
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The temperatures quoted were Farenheit. I let the car idle for a while then measured the temperatures. I don't want to get stranded driving the car again.

I've removed the exhaust pipes and looking into gutting the cats. I've never welded do I might try to cut the pipes, gut the cats, then use a splice to put the pipes together. But that would be four patches where I cut the pipes (2 for the primary cats, 2 for the secondary cats)

Because the pipes are bent, I really can't gut them because there's no access to either the inlet or outlet side of the cats.

Thoughts?
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post #25 of 43 (permalink) Old 01-29-2018, 03:25 PM
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The temperatures quoted were Farenheit. I let the car idle for a while then measured the temperatures.
I am sorry, but 130 F could be the air temperature in Phoenix, AZ in July. If that were the case, the converter will be blocking the exhaust gases almost completely and the right exhaust pipe should have almost no "pulse", have you checked?


Quote:
I've removed the exhaust pipes and looking into gutting the cats. I've never welded do I might try to cut the pipes, gut the cats, then use a splice to put the pipes together. But that would be four patches where I cut the pipes (2 for the primary cats, 2 for the secondary cats)
Another mention of primary and secondary cats, can you please post a picture? I am very curious.

v12 exhaust is like that: 1) a cat. converter (one for each bank), 2) middle resonator, and 3) rear muffler.
This is it (shamelessly lifted off of a post of another fellow with a M120):



I always assumed that all w140 are the same when it comes to cats and pipes.

G-AMG has nice pictures from a 1999 v8, for example.



https://www.benzworld.org/forums/w140...2-sensors.html

Does your exhaust look different?

Steve

Last edited by Steve_B; 02-17-2018 at 06:12 AM.
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post #26 of 43 (permalink) Old 01-29-2018, 05:27 PM Thread Starter
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Here's a picture of the exhaust I removed. It's take as if you're standing at the back of the car, so the cats nearest you are the secondary cats. The computer turned the pic sideways, so the cats on the right are the secondary cats.
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post #27 of 43 (permalink) Old 01-29-2018, 10:31 PM
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Steve,

I think I recognize that crusty looking exhaust system!

For a quick update, after I gutted the cats, the car ran much better. The idle was much improved, due to the ability of both banks being able to breathe freely.

I also disconnected the O2 sensors.

The car throttle is much crisper, and the running temperture has dropped at least 5 degrees (C) after that.

I am very pleased not only with the WOT performance, but also the day to day running. I've been driving it about 3 weeks since returning, and the car is almost a daily driver.

Regards
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post #28 of 43 (permalink) Old 01-29-2018, 11:11 PM
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Originally Posted by MercedesMikeNAtlanta View Post
The temperatures quoted were Farenheit. I let the car idle for a while then measured the temperatures. I don't want to get stranded driving the car again.

I've removed the exhaust pipes and looking into gutting the cats. I've never welded do I might try to cut the pipes, gut the cats, then use a splice to put the pipes together. But that would be four patches where I cut the pipes (2 for the primary cats, 2 for the secondary cats)

Because the pipes are bent, I really can't gut them because there's no access to either the inlet or outlet side of the cats.

Thoughts?
You are better off going to an exhaust shop and let them do it. It's not that expensive for them to cut, bend, and weld a new pipe in. You can buy a new cat online or let the exhaust shop get it for you. Also I would cut out the secondary cats if you have them, since they are not needed and they don't make a difference regarding emissions anyway.

If you live in an area where they put the car on a lift during a car inspection, then you cannot cut the cats. They do this to make sure you have all the cats there. If the shop doing the inspection does not inspect the car like that, and they only do an exhaust test (putting pipe on the exhaust and measuring emissions) then you can cut the secondary cats out with no issues.
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post #29 of 43 (permalink) Old 01-29-2018, 11:19 PM
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Secondary cats are the cats that are towards the rear of the car. Those are the ones that can cause engine when they got clogged. Primary cats usually never get clogged. If you remove the secondary cats the check engine will not turn on because of it so it doesnt harm the fuel trim ratio. Now if you remove the cats up front you will get primary cat check engine light. Here is the the down side. If you primary cats are busted already you will get a check engine light for emissions. To be honest on my s55 i had no cats kleemann headers i always had a check engine light but car ran flawless. Same for my 97 s500. I attached a picture of my cousins e55 with secondary and resonator delete and the secondary cats go where the new pipes start
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post #30 of 43 (permalink) Old 01-30-2018, 06:26 AM
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Here's a picture of the exhaust I removed.
Thank you. I took the liberty to edit your picture and added a few comments.

Please also refer to the attached .PDF.

EDIT: As far as understand it, the thingies in the middle of the exhaust which are suggested to be secondary cats in various posts could be in fact the main cats. Whether they are in use on all model years, and for all markets is unclear. They could be with the design of catalytic converters with ceramic core, but the function of resonators (or silencers). The parts catalog refers to those sections as "exhaust pipes" and provides no specifics.
StarTek from which the attached printout was originated has no information and only identifies the TWC close to the engine.

Attachment 2364953

There are two O2S (oxygen sensors) upstream the TWC, which are used for fueling. If their are faulty, your air-fuel mixture will not be right.

The second pair of O2S are monitors. They are for the US market and a primary source of Check Engine Light/. Their function is ONLY to measure the health of the converters.

To me, it makes no sense to have another pair of converters this far out and AFTER the monitor O2Ss.

As of cats failure -- wrong fuel mixture (rich) will cause the cats to heat up 900C and glow. The matrix inside melts and blocks the flow. Debris from the melted converter usually end up blown downstream and get stuck in the middle resonators (the cause of rattle and funny noises).

I hope this makes sense.

Good luck,
Steve

PS On an OBD-I car, as Peter's, one can run straight pipes and will have no problems.

On an OBD-II car such as yours, you can't fool the ECU.

Last edited by Steve_B; 02-17-2018 at 06:14 AM.
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