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Discussion Starter #1
Hey everyone, hope a great new year is in the works for all of y'all.
Question about o2 sensors. I want to replace all of them on my 99 s500 (w140). But I'm confused about model numbers. When I look it up some say front left or front right or downstream left or right. But they have the same model numbers. Regardless of what side. Why is that? Same thing when I looked at cats on magnaflows site. It listed a front right and front left cat but when I add to cart it is the same model. Any clarification will be helpful. I'm really hoping I can slap on the same o2s for all the bungs.
 

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Discussion Starter #2
According to PelicanParts, they have that the front o2s are interchangeable regardless of sides. So I think I'll order the same model for the front ones.
 

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'99 S420 116K
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What is the mileage of the vehicle?

Why do you want to change them all? Symptoms? CEL? Poor fuel economy? Codes?

I understand that they are considered expendables, so if one fails, it might be good to replace all at once, but without symptoms(CEL), i'm sure there are other areas to drop $500 into.:confused:
 

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Discussion Starter #4 (Edited)
Yeah, got a CEL, figure I should replace them all, one of the cats was clogged (secondary driver - now removed). s500 1999 w/ 115k miles
 

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'99 S420 116K
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Yeah, got a CEL, figure I should replace them all, one of the cats was clogged (secondary driver - now removed). s500 1999 w/ 115k miles

What clogged the CAT?

I doubt replacing the O2 sensor will remedy that.
 

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'97 CL600
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Logical, I ended up with a failed cat and I only have 70K on my '97 CL600. Have no idea what caused this. I switched to Magnaflows at $250 each instead of $1200 ea from MB. You can find Bosch replacement O2 sensors at amazon.com for about $60 each. While we replaced the two exit O2's we didn't replace the ones upstream of the cats. That will happen today. And yes, a pesky CE light is the reason.
 

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'99 S420 116K
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Clogged Cats are usually unburned fuel(rich mixture), coolant burning, oil burning. I'd bet unburned fuel combined with short trips, or maybe a long trip with a rich mixture.

Those cheaper Bosch O2 sensors are probably usable, but the $125 Bosch sensors are complete with proper wires, length, and connectors, and new rubber grommets.

When they get high mileage the oil burning becomes the issue, or a blown head gasket dumps coolant in a cat. This is why it's imperative to keep those O2 sensors operative and pay attention to the CEL situations.

My next question for the OP was if he noticed ANY smoke out the exhaust, or if the CATS were getting red hot.

Anzani, I like your remedy of replacing the cats, did you notice any operational changes, better fuel economy, more power? Will it pass state inspections?
 

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Discussion Starter #8
The issue was with the fuel pressure regulator. The car hadn't been ran since 2004 before I got it working late last year. The cat would turn red hot and on further inspection it was clogged and destroyed inside. Wouldn't take more that 2 minutes of run time to see it get near bright red on the driver side secondary cat.

My q is regarding the type of o2 sensor though, I'm going to replace them all since I'm getting codes for at least 2 (can't recall which ones). And I need to know if they are the same or different. According to PelicanParts the front are interchangeable so the same model works but the downstreams are different. Does this sound right?
 

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'99 S420 116K
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The issue was with the fuel pressure regulator. The car hadn't been ran since 2004 before I got it working late last year. The cat would turn red hot and on further inspection it was clogged and destroyed inside. Wouldn't take more that 2 minutes of run time to see it get near bright red on the driver side secondary cat.

My q is regarding the type of o2 sensor though, I'm going to replace them all since I'm getting codes for at least 2 (can't recall which ones). And I need to know if they are the same or different. According to PelicanParts the front are interchangeable so the same model works but the downstreams are different. Does this sound right?

Thank you for the explanation.

I would assume Pelican Parts is correct.

As a final word, you might check MB's recommendation for replacement O2 sensors.
 

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'99 S420 116K
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FWIW, I have found O2 sensors to have a useful lifespan of between 75K and 125K miles, barring any malfunction of the engine, excessive fuel, oil, or coolant mishaps.
 

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'97 CL600
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Clogged Cats are usually unburned fuel(rich mixture), coolant burning, oil burning. I'd bet unburned fuel combined with short trips, or maybe a long trip with a rich mixture.

Those cheaper Bosch O2 sensors are probably usable, but the $125 Bosch sensors are complete with proper wires, length, and connectors, and new rubber grommets.

When they get high mileage the oil burning becomes the issue, or a blown head gasket dumps coolant in a cat. This is why it's imperative to keep those O2 sensors operative and pay attention to the CEL situations.

My next question for the OP was if he noticed ANY smoke out the exhaust, or if the CATS were getting red hot.

Anzani, I like your remedy of replacing the cats, did you notice any operational changes, better fuel economy, more power? Will it pass state inspections?
I didn't notice much improvement because the car has always been a rocket. I made sure that the Magnaflows I ordered were CAL approved. In fact, I had to do the mandatory "smog check" recently and the car passed with flying colors. I think the original cats gave out because the car was in a marine environment for 15 years and was hardly driven. I buy it and bring it to the desert where the humidity is negligible. I think corrosion had already set in and my fast driving style with hours of wide open roads may have been too much. It gave no warning when it let loose. Since there are two on my car, I changed them both.
 

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Discussion Starter #13
I've noticed you mention that before and I'm sort of confused on the amount of cats the car has. Are there only 2 total or 4- Primary and secondary? I'm contemplating removing the secondaries and replacing the primaries for something better but the issue ends up being in the o2 sensors and their locations
 

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'97 CL600
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I've noticed you mention that before and I'm sort of confused on the amount of cats the car has. Are there only 2 total or 4- Primary and secondary? I'm contemplating removing the secondaries and replacing the primaries for something better but the issue ends up being in the o2 sensors and their locations
Chungas, there were TWO catalytics on my '97 CL600 (S600 coupe) There were two O2 sensors upstream BEFORE the cats and two downstream AFTER the cats. Then there were mufflers, etc. We replaced the two original cats with CALI approved Magnaflows. We then removed one of the two mufflers. This gave me a "throaty" rumbling sound especially when I start the car. The neighbor across the street told me he always knows when I'm leaving. The sound is not annoying especially at speed. I'm very pleased.
Anziani
 

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1994 S600 Coupe, 1995 S600 Coupe
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Early M120 engined cars with LH injection have one O2 sensor on each side. Late cars have two on each side.

For the late cars, you need two 0005407417 sensors, and two 0005407217 sensors.

Jon
 

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'98 S500, '99 S420 etc.
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Early M120 engined cars with LH injection have one O2 sensor on each side. Late cars have two on each side.
Jon
I'm working on a '95 S600, which has two O2 sensors and two cats and two "mufflers." I think exhaust guys would call the one behind the cats a muffler, and the one just before the tailpipe a resonator. I'm guessing that that last one was the one Anzani removed from his car to get a bit more "growl." Am I right?
 

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1994 S600 Coupe, 1995 S600 Coupe
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That would be my guess. He'll have to answer to make sure.

Yeah, your 95 will have one O2 sensor on each side.

Jon
 

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'95 S600
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I believe its market dependent also as my old Euro spec'd facelift car built Dec '95 had ME injection but only the 2 pre-cat sensors.
 

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'97 CL600
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That would be my guess. He'll have to answer to make sure.

Yeah, your 95 will have one O2 sensor on each side.

Jon
The muffler shop did the conversion but I think they removed the downstream mufflers but left the resonators. The staid old Benz now has a throaty rumble at times. Love it!
 
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