CA Smog

[Tom]

Tom is the CA smog whisperer.

I think it is true, though, that you can't get under all the CA limits with just a tune. You need a working cat too.

I'd say it's 'possible' for a 951 to pass without a cat, but everything would have to be exactly perfect. The car in question had an o2 sensor that was several years old, oversized injectors and 3 bar FPR, etc. It was also an '88, which has lower limits than my 86. The failing numbers we got would have been just under the 86 limits. That said, unless you are tuning during the test with real-time exhaust readings, the wideband alone doesn't give enough feedback to let you know when you're in that super sweet spot. Somewhere on my long list of forgotten projects, I meant to build a meter that shows what percentage of time the car is running above and below 14.7. The entire time we were tuning on the test, the car was dithering around 14.7, but adding a smidge of fuel would no doubt cause the car to spend more time below the target, etc. so if we could hone in on that sweet spot, we'd have another tool at our disposal. Now whether that sweet spot is the same from car to car is another questions, and I'd kind of guess not....

[cda951]

I don't have much to add to what Tom has already said, except to reiterate how important a stoichiometric mixture is, along with a good oxygen sensor that quickly switches up and down on either side of stoich.

I managed to get my VEMS-equipped 951 with 800cc fuel injectors to pass the less-strict "basic" CA smog test (idle and 2500 RPM in neutral, no dyno) by carefully tuning the VE cells in that region, and enabling the closed-loop WBO2 sensor feature in VEMS. This ended up mimicking the factory O2 sensor controller and the AFR wavered slightly and consistently above and below 14.7:1 when I got it right.

My original factory catalytic converter with over 170K miles on it is getting a bit tired, but is still up to the task. I feel that it if it had to pass the "enhanced" dyno test, it would likely fail on NOx. And that is the biggest hurdle for older cars passing CA smog: even the expensive, CARB-legal cats are absolute garbage and usually only last a few years.

Attached are some pics of my engine bay. A super-knowledgable old-school smog tech would find issues, but most do not know what they are looking at.

[Tom]

Wow, that does look pretty darn stock! It "seems" like most shops have become a bit more lenient on the visual over the years, so something like would pass the visual just about every time I suspect. Back in the 80's, I once had to 'buy' a $20 wingnut from a smog shop for the top of an old V8 air filter lid because the hex nut I used 'didn't pass visual.' The 'test only' centers did away with those kinds of shake downs, which were all too common. But also, because smog testing is their sole source of income, 'test only' centers have incentive not to be known as nit-picky. Thanks to the internet, if a shop failed this car because of the Laust manifold or whatever, it would be all over Yelp and hurt their business. Not to mention most shops give free or half price second tests -- so nit-picking little things just means they doubled their work for no particular reason. Just my two cents....

Are you using the air flow meter to actually measure air, or just to keep the stock look?

Do they not test NOx on the 'basic' test? That's the bugger that makes the whole thing such a balancing act....

[cda951]

Are you using the air flow meter to actually measure air, or just to keep the stock look?

Do they not test NOx on the 'basic' test? That's the bugger that makes the whole thing such a balancing act....

If you look closely, there is no AFM whatsoever, VEMS uses MAP/speed-density for air mass estimation. I hogged out a factory 1980s BMW AFM adapter tube to 3" ID, and have a black silicone coupler with a sleeve connecting to a Lindsey J-boot. Again, this would not fly if the smog tech is familiar with Bosch L-Jet and/or its successors . . . .

As for NOx, the "basic" test does not consider NOx, since meaningful emissions of this pollutant are only emitted when the engine is under load, hence the dyno test in more densely populated "enhanced" areas of CA.

[Tom]

Nice work -- looked like a real AFM to me. Is the air flowing through the stock filter box this way? Have any pictures of what you did there?

Very jealous of no NOx limits! DEC stopped making their cheap-o direct-fit cats, so I am nursing the last one I bought in ~2018. Two tests passed with it, but at some point I suspect I'll be welding cheap-o universal CA cats into these pipes every two years