I heard that over inflating the rear tires since it is RWD will help a closely failing vehicle.

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William
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1987 420 SEL - Like a fine wine only better with age

How does the car know the speed?
Can it be altered a bit by different wheel/tire size?

Seems to me RPM
no is that the rear wheels or the cam?
Or does the cam revolve as aresult of the rear wheels driving it...

What I am gettin gat is
I got really low rpm on my car
15 & 25 mph were in the 1300 range.

I;m wondering if & how that coudl affect a smog test?

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83 500 SEC Euro 198K

For what it's worth, most NOx issues are EGR related.

That's the tough part...the 260E has no provision for an EGR valve other than a untapped bung on its exhaust manifold. High NOx tends to indicate high combustion temperatures.

Because your other numbers look okay, ensure that you're running the highest possible fuel octane to ward off detonation (pre-ignition) and that it is as close as possible to 87C (thermostat opening temperature) when the test is conducted. Let us know how it goes...

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one neat trick on a car that is that clean and close to passing is to inflate the rear tires to 45psi because on the dyno you have two bags on the tires not one and it takes power to move those bags around the wheel.from what i see of your results you could also richen up the mixture about a 1/16th of a turn.more fuel means less o2 available for making nox and you have room in your results for a little more hc and co.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg

Altering the initial mechanical mixture adjustment will have no significant effect unless it's altered beyond the ability of the lamda system to maintain stoichiometry, which will probably knock all the gases beyond the cutpoints.

The 0.1% O2 reading indicates the catalyst could do a little more if it was hotter, but your HC and CO are good. The biggest problem on these engines is usually meeting the 15 MPH HC cutpoint when the catalyst is coolest. That's why the engine should be as hot as possible when you start the test.

NOx generation is a function of peak combustion temperature. (It has absolutely nothing to do with coolant temperature.) Retarding timing will reduce peak combustion temperature. Initial timing is fixed and not adjustable, but you can replace the short vacuum advance line rubber hose from the manifold to the nylon tube that routes to the EZL module with another piece of rubber hose plugged with a slug of silicone sealer, and/or you can replace the R16/1 resistor with a shorting plug that you can make out of a piece of wire. This will reduce spark advance at the speed/load conditions of the test and dramatically reduce NOx. It will also increase EGT, which will heat up the catalyst and allow it to promote more reactions, likely consuming the last remaining fraction of O2.

The above is thoroughly discussed in other threads in the last couple of years. Search under my screen name.

And please post your final test results.

Duke

DITTO...

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William
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1987 420 SEL - Like a fine wine only better with age