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Old 03-30-2003, 09:10 PM
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ILUVMILS: Sorry, didn't know you were a "seasoned tech". Didn't mean to disrespect you or anything. Just remember, I'm agreeing with you on this!
'86 420SE Euro
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Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."
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Old 03-31-2003, 11:43 AM
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Location: Ontario, Canada
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I think responses should be devided into two categories.
OPINIONS & SUGGESTIONS ( when you are not sure ) would be one,
the other is FACTS ( when you are certain ).
Sometimes, the nature of the response may determine if somebody runs & throws many unnecessary dollars & parts at a problem, based on what they are told here.
One should therefore specify, if their response is opinion or fact.
2007 C 230 Sport.
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Old 03-31-2003, 12:38 PM
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Location: Evansville WI
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I'm no chemist, and there is no emissions testing where I live, so I'm no emissions specialist really, but Nitrous Oxide is laughing gas, which is used by ricers and racers to get more power than is normally available form their engines. Oxides of Nitrogen (NO) is an emission gas I believe, not Nitrous Oxide (NO2), different things. There are many links in the web to indicate both Nox and NO2 are the same thing, but I believe (and maybe there is a chemist out there reading this who can clarify it) but I believe NO is the chemical nomenclature for the "bad" stuff, and NO2 is the stuff dentists and ricers use.
Possibly "NO" is Nitrogen Oxide and NO2 is NitrOUS Oxide?

There is no emission related sensor that analyzes exhaust gases EXCEPT an 02 sensor (Oxygen sensor) and that's all it can sense is the presence of oxygen molecules. It senses "rich" as the lack of oxygen molecules and "lean" as a higher presence of oxygen molecules.
There are now a couple sets of O2 sensors, depending on exhaust system configuration, which senses how efficient the catalytic converters are.

I've never hear of a knock sensor referred to anything other than a "knock sensor", and there is no "NOx" sensor.

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Old 03-31-2003, 04:27 PM
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OK, I have done some research. I would like everyone to know that I am sorry, and that I would like to you to read this post, for I fell that it is far more accurate than my previous posts.

There is no such thing as a NOx sensor.

A knock sensor, is usually found on cars with high compression engines. The knock sensor senses the vibrations of the engine block due to predetonation of the fuel in the combustion chamber. The knock sensor tells the car computer (EMC) to retard the timing of the engine to avoid pinging- which causes serious damage.

When the fuel mixture is too lean, it becomes very hot, and everything about what I said before: "because of the lean fuel mixture which makes the bonds of N2 which is regularly found in air at close to 80% of air to combine with O2 to form N20, NO, N2O5, and other NOx mixtures. Instead of N2 being a non-reacting molecule passing through the engine, it reacts with air at high temperatures to form N20, NO, N2O5, etc. Basically N2 + O2 ~~~> NOx emissions, which is an endothermic reaction (requires heat to react)." The EGR valve lets some exhaust gas back into the engine to lower combustion temperatures to reduce these types of emissions. The knock sensor has nothing to do with this.

I spoke with my brother about knock sensors, he said if you were to hit the side of the block with a hammer (not endorsing this), and the the engine started running bad, then you would know that the car has a knock sensor because it sensed the vibration and retarted the timing.

I spoke with a Mercedes Tech about the SL600. He said if the car is pinging, check to see if you are running premium. You said you were, so thats probably not the problem. The next thing it to make sure that the knock sensor is working-retarding the timing.

For Gilly,
Ricers use Nitrous oxide which is N20.
N20 Nitrous oxide (old naming) Dinitrogen monoxide (new naming)
N0 Nitrogen monoxide
Nitrous oxide is used by ricers to provide more oxygen for the fuel to burn, but consequently they dont care about the emissions of their car when they are racing.

Very sorry for the poor information. I hope this has helped clarify the subject and help you know what to do with your SL600.

No Benzes in the stable at the moment, but itching for one again.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 300E Amg Hammer 88k mi sold
1992 500E 156k mi sold
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Old 03-31-2003, 04:53 PM
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Here is a link to a good page I found regarding nitrous oxide injection, in case anyone is interested:

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Old 03-31-2003, 08:47 PM
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You are forgiven. ( Because you have Senior member status ).
2007 C 230 Sport.
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Old 03-31-2003, 11:33 PM
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It sounds like my simple question elicted much sound and fury!. To push the issue further in a constuctive manner how do I get the trouble codes on this car?.
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Old 04-01-2003, 10:35 AM
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Location: Dallas/Fort-Worth
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How about another uninformed opinion?

Check vacuum lines and inspect for any breaches in and around the intakes.

If the combustion chamber is sucking more air than what would normally be "metered", that would cause a lean condition, especially under "load".

I would presume that the engine management system would compensate for that, but it would be something I would inspect.

BTW, how long has this been occurring? Any recent repairs done in the engine bay prior to the incident?
2009 ML350 (106K) - Family vehicle
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