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Old 11-05-2002, 09:03 AM
Registered User
Join Date: Oct 1999
Location: Richardson, Tx
Posts: 25
Emissions Gurus please read and reply!


I need help. My 87 190e 2.3-16v (replaced motor with a Euro spec) has now failed emission testing twice...the first time I expected it.

The catalytic converter was clogged up, so I kinda helped it "breathe" a little better and knew the car would fail...I wanted to see how badly, though.
Here are the numbers for the first test: (just the high speed)

----------------Standard-------Current Reading

As you can see, only the HC reading was through the roof.

Now, here are the numers AFTER I replaced the cat:

-----------------Standard--------Current Reading

Someone please tell me how in the heck the Nox shot up like that!

Could a new catalytic converter cause this emissions nightmare?

Note:Over the past few days, my car will, without warning, shut off. All I have to do is restart it, though...could this have something to do with it?

Gurus, please help!

87 16v
00 ML430
00 ML55
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Old 11-05-2002, 09:59 AM
Posts: n/a
Well, tthe numbers are certainly odd. I have no explanation for the drastic increase in NOx, except for possible error on the part of the inspector or analyzer.
So, I have 2 suggestions.
1. Clean the EGR, test for function, clean the exhaust gas tube that goes to it.
2. ask the manager, or call the company office, ask to speak to the QA technical person, or call the Texas Dept of Public Safety 1-800-396-9394 ask for Santos Olivarez, which I believe oversees the emission testing, ask them when the calibrations for the analyzers are done, then try to test as soon as possible after the cals are done.

Good Luck, and thank you for your help to clean the air.
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Old 11-05-2002, 02:42 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I am not real familiar with the cats on 16v cars. The standard 2.3 cats have NOX precats right at the connection to the exhaust manifold and use the engine heat for the catalytic action.

Most aftermarket cats are about 1/3 the size and have all three components under the car. I have no experience solving NOX problems as we have no testing at all in Florida, but its concievable that the aftermarket cats do not perform well for NOX due to size and placement. The oxidation section of the cat is always under the car and was probably the part of your original cat system that was bad thus giving the appropriate oxidation values while dropping the reduction component.

Just a guess.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 11-05-2002, 04:50 PM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Here in Alanta we have the highest level of emission testing other than Calif. STEVE is 100% correct, unless you paid $2000. for the cat you didn't get pre-cats & that would be why the NOx went UP!
The 16V didn't have EGR so don't worry about that.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator
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Old 11-05-2002, 10:41 PM
Registered User
Join Date: Oct 1999
Location: Richardson, Tx
Posts: 25
First of all, thanks guys for the input...I appreciate it.

Here's what I found out today:

From the Texas Dept. of Transportation:
I was quite fortunate in reaching the main emissions guy in Austin who had a few suggestions as to what was wrong with my car's emissions.
1. The muffler shop put the wrong type of catalytic converter on my car...a two "something" instead of a three "something" (I forget the word).
2. The new cat might have been contaminated or faulty.

From a pretty good mechanic:
1. See above answer #1.
2. The muffler shop could have put the cat on backwards.

From the muffler shop:
1. No, we put the right catalytic converter on there...and yes it was a three "whatchamacallit", too.
2. The catalytic converter we took off was completely had NOTHING in it!
3. We put on a "universal" can't be put on backwards.

Here is what I don't get:
1. M.B. Doc, I don't know what EGR is or stands for...are those the pre-cats Steve was talking about?

2. If 16v's do have pre-cats, and they were working before WITHOUT the third lower cat, how come they stopped working when a new lower cat was installed?

3. If 16v's don't have pre-cats, how does putting on a new catalytic converter cause anything worse than NO CATALYTIC CONVERTER AT ALL???? My old catalytic converter was just a shell!!!

4. Mr. Moderator: Are you sure my cat would cost $2,000???? I looked up my specific model catalytic converter on several mercedes autoparts websites...they ranged from $100 - $300.
If the replacement 16v catalytic converter is $2000, how can anyone justify paying that much for one?

5. I watched the muffler guys remove my catalytic converter and replace it with an identical looking wasn't smaller or different looking in any respect.
87 16v
00 ML430
00 ML55

Last edited by Andrew; 11-05-2002 at 11:09 PM.
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Old 11-06-2002, 03:56 AM
Posts: n/a
I'm looking at replacing my entire exhaust system on my 88 300E due to rust and a crack in the converter and have been shopping the net. A company called sells complete exhaust systems for MB cars for around 800 bucks. This includes cats, mufflers and pipes. It is a stainless steel exhaust system too. I've had positive feedback regarding timevalve from some of the folks on this site. I've heard mixed messages about chain type muffler shops for MB replacements so I'm thinking of going with timevalve and having an MB independent service place install it. If you replaced the entire exhaust system and the car still didn't pass emmissions I would guess that something is going on with your new motor. In any case you could try to find a local independent shop "make" your car pass emmissions. What they do is adjust the fuel mixture on the car to lean it out during the test. The car will run aweful during the test but the emmissions will be low and it will pass. Once the test is done they just reset the fuel mixture back to its normal setting. Of course this is not the best solution but it is a temporary solution.
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Old 11-06-2002, 06:59 AM
Posts: n/a
I am very disappointed in the above method of "passing" the emissions test.

First of all nobody really likes the hassle and cost of emissions testing, it was a mandate from EPA via congress and the CAA of 1990, BUT what MADE the emissions testing happen was just such methods mentioned above, ie many polluting cars.And as I tell citizens here, if you think its an inconvenience now, how will you feel when it ( air quality) gets so bad that your kids will not know the joy of driving a vehicle, because they will no longer be allowed to own one. If you think this will never happen, think again about all the things one thought would never happen and they have indeed come to pass.

secondly, I have an 87 300E that was 80% below the allowed emissions limits for HC, 47% below for CO and 68% below for NOx. Why? proper maintenance, replacing the O2 sensor at 60K, then again at 120K, new cat at 100K.

third, I believe that there is not a way to "lean out" a 300E without really screwing it up because of CEC's.

But, at least for now it is still a relatively free country, at least in theory. Good Luck
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Old 11-06-2002, 08:56 AM
Registered User
Join Date: Jul 2002
Location: Dallas
Posts: 330
I have heard lots of complaints about emissions testing in Dallas with the new law, new equipment, and new technicians. Many people are failing emissions testing and going on a wild goose chase only to find out later that the problem was with the equipment testing their car. I just wonder, if you took the car to another place to have it tested, your problem might disappear as mysteriously as it arose. I dread my first "new" inspection in January.

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Old 11-06-2002, 10:41 AM
Posts: n/a
Of course I was only suggesting a temporary solution until you can get your car fixed properly. There are fewer things more frustrating in the car world than having a perfectly nice Benz you can't drive because you can't get it to pass a stupid emissions test.
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Old 11-06-2002, 11:45 AM
Registered User
Join Date: Dec 2000
Location: Battle Ground, WA
Posts: 576
Excessive nox emissions...

Hi there,
I think you need to go back to the original problem, the high hydrocarbons. The reason I say this is that you have very high nox emissions. These are caused by excessively high catalytic converter temperatures. I'm thinking the reason your cat is so hot is because it's getting too many hydrocarbons, and burning off the hydrocarbons is overheating the cat converter. The EPA has released a report that states that catalytic converters are contributing to global warming by causing excessive nox emissions to occur, and this may someday be the reason for their eliminating catalytic converters on tightly controlled fuel injected gasoline engines. That's not going to happen overnight, however, so why don't you get the engine tuned up and fix the original problem? My 1982 Mercedes 300D with the 4.3 liter chev V6 installed passes with NO catalytic converter, with much lower hydrocarbon numbers than you are showing. It shouldn't be very difficult to maintain an idle speed hydrocarbon measurement of under 150 ppm, and a 2500 rpm measurement of under 75 or so. Those are the numbers my engine posted last emissions check. (Washington State) You can't fix an out of tune engine with a new cat!

Richard Wooldridge
1982 Mercedes 300D/4.3V6
1994 Ford Taurus
1988 Chev Astrovan
1977 Jag XJ6L
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Old 11-06-2002, 08:03 PM
Registered User
Join Date: Oct 1999
Location: Richardson, Tx
Posts: 25
Richard, either you work for the Texas Dept. of Transportation, or you're just pretty dang smart...

A gentleman from the TDOT called me today regarding a message I left yesterday when looking for someone to explain my Nox emission problem.

He was very methodical, and I think pointed me in the right direction for solving this dillemma. He did it with just two questions!

1. Why were the HC's high in the first place? The answer was a messed up catalytic converter.

2. What caused the catalytic converter to fail?

He then went on to explain that an engine running too rich is almost like pouring gas on a fire. A catalytic converter exposed to too rich a mixture can get hot enough to melt! According to his experience, he's seen a new cat destroyed by over an over rich engine in just one week...although, I doubt my case is that extreme.

I attatched a NOTE: to the bottom of my first post, mentioning that my car had recently been shutting off spontaniously...almost like it had been flooded. BINGO!

Anyway, I'll start there and see what happens.

Oh, by the way, Dave I think you might be right about one thing: The tech who tested my emissions the second time was a snot nosed kid who stalled my car SEVERAL times trying to drive it onto the test ramp. Everyone in the bay kept laughing at him...I probably should have asked for the first guy.

Thanks to all who replied,
87 16v
00 ML430
00 ML55
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