Passed CA Smog!!!

[Tom]

Fast forward another 2 years and happy to report I passed smog today, but not without some effort.

Hi Tom - where did you take it this time around?

I need to do my Cayenne for the 1st time and it might be good to warm up the relationship before I present them with the 951.

Thanks!

Mike

Sorry, have been out of town. I take the 951 to Smog It Mercedes Service on Evelyn in Mt. View. The tech is quiet and a bit hard to read, and does all testing by the book but without any game playing or going out of his way to find ways to fail the car. I used to go to a guy that would hem and haw about nonsense trying to get a 'tip' -- but happy to say BAR finally caught up with him. So I'm happy with the Smog It guy just to avoid that kind of thing. If you take your car there, be sure to remind him that both the 15mph and 25mph tests can (and per the regs, should) be done in second gear. He has a tendency to want to shift to 3rd for the 25mph test, which meaningfully increases the emissions numbers. He's not at all cheap though, so for a Cayenne (where they only really check for computer errors), I'd be inclined to go to an OBDII only place with commodity pricing. I used these guys last month on a modern Toyota and they were fast, cheap and easy... https://www.yelp.com/biz/campbell-every ... 2c82d02526

[whalenlg]

Thanks - I’ve been there twice with no bs, so I’ll plan on returning.

[Tom]

Thanks - I’ve been there twice with no bs, so I’ll plan on returning.

Which one? Smog it?

[whalenlg]

Thanks - I’ve been there twice with no bs, so I’ll plan on returning.

Which one? Smog it?

Yes - smog it

[Localracer]

Tom,
Congrats on smog pass.
You mentioned NOx are going up.
Cats control HC by oxidizing the unspent fuel (hc) to CO and CO2 .
NOx are formed at higher temps which is why the old air cooled motors generate high levels.
Next smog, try running a 10 gallon tank of gas with OxyCat to clean up the cat surface. Then run a mix of higher octane lead free fuel, like Sunoco or VP fuels with premium pump gas. Try a 20% mix of 100 octane. Octanes are additive so you can estimate the octane you are at with the mixture. Higher octane fuels burn cooler and will reduce the NOx made. However, the HC and CO may increase. Look at you last smog checks and be sure there is room to increase the HC and Co before maxing the limit. So be sure cat is clean and at full operating temp before taking it into the smog check.
I learned this from a chemical engineer after changing ecus, fuel injectors, maf, cat. It is low cost, legal and keeps your car running clean.
Good luck.
FYI, i was over Nox max by a few hundred ppm. I was at 1% of max HC and CO, so numbers could increase 100X before I failed. NOx dropped 300, HC increazed only 25% and I passed with just adjusting the octane of fuel I was using.

[Tom]

Tom,
Congrats on smog pass.
You mentioned NOx are going up.
Cats control HC by oxidizing the unspent fuel (hc) to CO and CO2 .
NOx are formed at higher temps which is why the old air cooled motors generate high levels.
Next smog, try running a 10 gallon tank of gas with OxyCat to clean up the cat surface. Then run a mix of higher octane lead free fuel, like Sunoco or VP fuels with premium pump gas. Try a 20% mix of 100 octane. Octanes are additive so you can estimate the octane you are at with the mixture. Higher octane fuels burn cooler and will reduce the NOx made. However, the HC and CO may increase. Look at you last smog checks and be sure there is room to increase the HC and Co before maxing the limit. So be sure cat is clean and at full operating temp before taking it into the smog check.
I learned this from a chemical engineer after changing ecus, fuel injectors, maf, cat. It is low cost, legal and keeps your car running clean.
Good luck.
FYI, i was over Nox max by a few hundred ppm. I was at 1% of max HC and CO, so numbers could increase 100X before I failed. NOx dropped 300, HC increazed only 25% and I passed with just adjusting the octane of fuel I was using.

Thanks for the suggestions, and welcome to Carpokes!

In my case, the cat had simply been compromised by some earlier tuning efforts. CARB-certified cats are three-way converters, meaning they also contain (primarily) rhodium to control NOx, and the 951 is notorious for producing plenty of NOx. Unfortunately, aftermarket replacement cats generally have much less Rhodium (among other things) compared to the original factory cats, so they tend not to last as long or tolerate much rich-running hot-rod tuning. Mine had become virtually inert. A new cat, with no other changes, brought all the emissions number comfortably below their respective limits. It also didn't help that the tech lugged the car in 3rd gear on the first test -- that alone may have pushed me over the limit, or darn close...