I have a 89 300E in N. Cal. and I just passed my smog test.
HC CO NO
CO2 O2 Max Meas Max Meas Max Meas
15MPH 15.1 0.1 110 83 0.71 0.18 772 456
25MPH 15.1 0.1 85 81 0.59 0.23 711 435

It looks like my HC was pretty close to the limits at 25MPH. Reading what Duke2.6 has to say, my converter may have been too cool with O2 at 0.1. What would it have changed if my O2 was 0.0? Just seems too close to becoming a gross polluter. At least I am good for another two years.

I changed the plugs and ran Ventil Sauber cleaner into the tank.

If the catalyst is hot enough to consume that last 0.1 percent O2, it will probably knock the HC count down by at least 20 PPM. On my last test the HC reduction on the 15 MPH test was 40 PPM compared to the previous test. Often these M103 engines are near the HC limit with 0.1 percent O2 on the 15 MPH test, but this first test heats up the catalyst so O2 drops to 0.0 percent on the 25 MPH test, and the HC is not as close to the limit.

It's very simple to make a shorting plug for the R16/1 trim resistor to slow the centrifugal spark advance, and take a short piece of 1/8" vacuum tubing, plug it with a slug of silicone sealer and substitute it for the molded piece of tubing at the manifold end of the vacuum advance line to the EZL module to disable the vacuum advance.

You can see how this reduced the emissions on my California ASM test. My primary objective was to get more HC margin on the 15 MPH test, and the side benefit was a dramatic reduction of NOx though this was not an issue with my car.

http://www.peachparts.com/shopforum/showthread.php?p=833484#post833484

BTW. in order for a car to be tagged "gross polluter" the measured emissions have to be about DOUBLE the limit, so your car would be a long way from that if you only experienced a marginal failure on HC.

Duke

When you say shorting plug for the R16 resistor. Is that like removing the resistor? Or am I grounding it out.

A "shorting plug" just shorts two leads together by directly connecting them with a zero resistance element.

A zero resistance R16/1 (which is a shorting plug) yields the slowest rate of spark advance with RPM and the least total advance. I didn't try to buy a zero ohm R16/1 at the dealer (may not be available in the US since it was never included with a US spec car), but it's easy to fabricate one for temporary use by just cutting a 1-2" section of 10 or 12 gage wire, strip both ends and fold the copper strands back over the insulation, bend it into a U-shape, then stick it in the connector, and tape it back up as it was originally with the 750 ohm resistor so there is no obvious evidence of tampering.

If you want to get fancy, you could buy another 750 ohm R16/1, remove the cover, then solder in a thin piece of wire to short the little resistor. Being as how I will only need my homemade shorting plug for a couple of hours every two years, it's good enough for the purpose.

Removing the resistor (which is the "open circuit" condition) yields the quickest spark advance rate and total advance, but the difference between open circuit and the 750 ohm resistor on US models is not much.

Right now I'm running without a resistor, 87 PON fuel, and am not getting any detonation as long as the engine temp is below 90 and the ambient temp is below 70. Above these values I get a little transient detonation if I short shift and apply the throttle too rapidly, but can "drive around" this by shifting at higher revs and easing back on the throttle. There's no detonation at WOT and medium to high revs, and I suspect the transient detonation is just a result of lag in the vacuum advance pulling off when the throttle is opened quickly.

Duke

I have the R16 in and have been toying with removing the resistor. Even with it installed, I get a few pings running prem. fuel. with air temp in the 60's and engine running close to 90C. You are running 87 octane with the R16 removed without pinging. I will have try it out.