Only reason I am not 100% sure about running rich is that I was getting this mileage before when I had 0.10ppm on HC.

I will do a little catchup on the ignition system -- Rotor + Cap, BP5ES (BP5EF) plugs, and splice in a new Bosch 13953 O2 sensor since all those items are at or very near recommended change intervals.

Duxthe1: I had the fuel distrib + eha rebuilt by larry @ CISFlowTech 2 years ago so I can guess everything with those 2 items should be OK. I guess I will run a fuel pump volume test to make sure everything pump-side is OK. Once all that is done, I will check mixture and make sure its not showing rich as you suggest.

Duke -- I thank you for the help at the prior emissions. I managed to get it to pass with the R16/1 shorting...but BARELY. Shorting it did not give me huge differences, so this time around I left it alone to see how she would do as-is.
I am also concerned about the Magnaflow cat. I had it installed in 2008...so its been 5 years and I do not have any precats so its fronting everything itself. Its a dang shame you can't "just" buy the OE cat and install it -- you have to cough up $2k for the entire pipe which I just simply cannot afford, nor is it cost effective.

Plan is to do the above, and then gauge results afterwards to see if I should get the Magnaflow replaced. Sucks emissions is a little bit of a crapshoot since everything is somewhat inversely proportional so nothing is ever 100%.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

For my wife's Honda (1990 Accord LX), a number of items were replaced and it passed like a new car. Pre-test numbers; HC = 72ppm and NOx = 536. PCV was toast as was air-filter, original O2 sensor and, original cat @ 148k miles!

Direct link here. Unfortunately, replacement cats have a very short life so I'm told.

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Regards . . . . JimF
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'94 S500 Cpe

Visit my Mercedes Web Page

Make sure you plug the vacuum advance signal line to the EZL module, too.

Unfortunately a lot of owners replace the OE catalyst way too soon IMO. Catalyst aging increases the temperature required to achieve maximum oxidation/reduction reactions, but retarding the spark advance map really helps by reducing engine-out NOx dramatically and increasing EGT to get the cat really hot during the test. The hotter the cat, the more reactions it will enable.

In the California ASM test the 15 MPH segment is done is second gear (I have a five speed manual in my '88 190E 2.6), which is about 1500, and with the R16/1 connector shorted and the vacuum advance blocked, no advance is added to the 9 deg. initial.

I always ask them to do the 25 MPH test in third, which is also about 1500, but sometimes they do it in second, which is about 2600. The numbers in both cases are about the same even though there is more advance at 2600 - probably because the 15 MPH test gets the catalyst very hot.

I believe your test is I/M 240, which has more speed and load variation, but retarding the spark advance map should have similar results assuming the cat is in reasonable working order.

The problem with my car was high HC at 15 MPH. It never failed but was at 90+ percent of the cutpoint. What really surprised me is the dramatic reduction in NOx. NOx is produced in the flame front at over 4000 deg. F. If timing is optimum for maximum torque at a particular operating condition, peak combustion temperature is about 4500F, but reducing it a few hundred degrees can dramatically reduce NOx formation. This is what retarded spark advance and EGR do - reduce peak combustion temperature.

Lower peak combustion temperature also reduces torque output, so where does that energy go? The First Law of Themodynamics says that energy is conserved. We have to accout for it, and that energy which would otherwise produce torque ends up going out the exhaust in the form of higher EGT, which adds more heat to the coolant as it passes out the exhaust ports and heats up the catalyst.

Duke