Clean Air test FAIL & PASS results- Confusing !
 

After miserably failing the clean air test one day then passing the next day after only increasing the idle .
The First test results which FAIL were as follows :
at curb idle 678 RPM
HC -- limit 300 reading 650 -- CO limit 1.50 reading 8.18-----
At 1644 RPM
HC-- limit 90--reading 334---CO--limit ,50-- reading--8.41 NO-- limit 979 -- reading 36

The strange thing to me is that just by increasing the idle a bit the HC, Co went down BUT the NO went up dramatically. PASS results as follows.
At 1671 RPM
HC reading 68---- CO reading 0.04 -------- BUT---------NO ppm went up to 354
I know at this point it's all just academic but are these cars so finicky ?

ALSO since I am typing away - can anyone please tell me the engine specs for my 1986 300E -- does it have a 3 L or 3.2 L what is the horse and torque power?

Cant help you with your first question, but here is some info about your 300e taken from the cars section of this site:
The M103 3.0 liter inline 6 engine in the 1986-1992 300E's displaced 2962cc's or 180.8 cubic inches. While in SOHC 2 valve per cylinder trim it made 177 horsepower @ 5700rpm and 188 lb-ft of torque @4400rpm.

Was your car cold during the first test and well warmed up during the second?
High NOx emmissions come from high engine opperating temps.
High HC emmissions come from a cold or worn out Catalyst that can not convert unburned fuel molecules (Hydrocarbons) by combining them with all available Oxygen molecules.
I think.

Thank you !
 

:) Thanks for specs !

NOx has nothing to do with "operating temperature" as expressed by coolant temperature. NOx is produced in the combustion flame front and is a function of load, A/F ratio, and spark timing.

See my previously referenced threads on the effect of engine timing on NOx.

Duke

So higher flame front temperatures produce more NOx?
Is there a inverse relationship between HC and NOx under correct opperating conditions?
I am still trying to understand these concepts.
http://www.naftc.wvu.edu/technical/indepth/CNG/CNG2.html

No, there's no simple relationship between NOx and HC. Lowering peak flame front temperature by retarding timing will reduce NOx, without much effect on engine out HC since engine out HC is primarily a function of A/F ratio and design issues such as quench area.

So lets take the A/F ratio out of the equation by assuming that the lambda system is operating properly and maintaining stoichiometry. Retarding the timing under any engine operating condition will reduce peak flame front temperataure, which will generate less NOx, and reduced timing will also increase EGT, which will increase converter temperature. So you end up with lower engine out NOx, about the same engine out HC and CO, but since the converter is hotter both its oxidation and reduction efficiency increases, which should lower all emissions at the tail pipe.

For a loaded test that measures NOx, the parameter that tells you how well the converter is operating is O2 content. If it measures zero, the converter is operating at or near peak efficiency. If it more than zero, it is not - probably because it is too cold - and this will usually show up as high HC - often near or over the test limit.

I retarded my timing map to reduce HC, which is the result I got - lower HC and reduction of O2 content from 0.1% to 0.0%, which meant the converter was operating at higher efficiency. I also expected to reduce NOx, but the 90 percent reduction really surprised me, and most of that reduction was likely in the flame front (lower engine out NOx), not due to better converter efficiency though it probably helped.

http://www.peachparts.com/shopforum/tech-help/117048-successful-ca-asm-emission-test-ke-fuel-system.html#post833484

Duke

HC= hydrocarbons thats what gasoline is made of. If your engine is emitting too much HC it has a miss or some other problem that is preventing all of the fuel from being burnt. In the above example the engine was running too rich. I can tell this because your CO was at 8%. CO or "carbon monoxide" is tied to fuel mixture the richer the engine runs the more CO. The O2 sensor or "exhaust gas oxygen sensor" on you car will attempt to keep the CO level at around .7% Some will run a little richer some a little leaner depending on the engine and temp of the sensor. NOx nitrogen oxides are a result of heat and pressure in the combustion chamber the greater the combustion temp or heat the higher the NOx. The reason the NOx was so low because you had too much fuel resulting in incomplete combustion and thats where your HC came from.
It's true that cat convertors reduce all of the things (provided it's a 3 way) they should not be high in the first place and to adjust your engine with a gas analyser you have to measure in front of the convertor, most euro cars have a provision for this. Something must be wrong with that car if it was running at 8% CO even if it was cold. That much unburnt fuel and CO will ruin that cat and I bet they are expensive on a benz. P.S. I am an ex Canuck pm me please tino

NOx engine out is maximum at about 10 percent excess air, which is quite lean. As the mixture is richened engine out NOx declines. Once the mixture is richer than stoichiometric NOx drops rapidly due to its effect on cooling peak flame front temperature. Running slightly rich was actually an NOx emission control strategy back in the seventies. Then the high HC and CO was was cleaned up with air injection and a two-way (oxidation only) catalyst.

Your first test numbers indicate about 30 percent excess fuel - the engine was obviously not in closed loop mode. In fact, it appears that it was tested virtually stone cold.

Did you just drop off the car at some shop and come back later?

Your second test numbers indicate a properly functioning lamda system and a hot catalyst. The NOx went up because the mixture was stoichiometric rather than way rich, but it's only about one-third the test limit.

Duke