Hi,

A few weeks ago, I had to do my bi-annual smog check. I had not been using my car for most of the spring, since I had another car, which was parked in front of the garage, easier just to drive that instead. I guess the car had been sitting in the garage for about 4 months or so, maybe out once or twice for small rides, had to fill up gas and did at the local gas station, Arco.
I took it to the smog and it failed miserably.



The car is a 1999 996, with 86k miles on it, and around 21k miles on a new engine. I doubt very much that there is something wrong with the engine.
I remembered that my friend also had problems passing his big old Dodge van after filling up gas from Arco a few months earlier. Could that be it? Hmm.
I started reading the threads about passing smog, read about all these additives that can be added to make it pass smog, guaranteed... Well, almost
I started driving the car every day for a week or so, tried to get the old gas out of the tank for sure. I filled it up with Chevron's finest and added a bottle of this Techron. Drove it until the tank was almost empty and filled it up again at Chevron, with another bottle of Techron
I spend half an hour before the smog test to get the operating temperature up and I drove confidently to the smog place. Some old dude in an RV from 1986 was there for 45min, he passed. I thought, yes, if that monster will pass, so should mine with flying colors.
I had left the car running for the entire time, so I should be nice and warm, ready to pass the test. Typical sunny summer day in SD, 10am and 90 degrees and totally dry.



What? It failed again, but a lot closer now. Back to the computer and do some more reading.
The primarily reason why the NOx is failing could be too high temperature in the engine during combustion? Air getting into the cat???? Catalytic converter is bust? The engine is running lean? MAF faulty? Water in the gas, standing still for too long?
I have to admit, I did not prepare very well for the test, thinking I would pass without any problems.
Now, my tags expired in June, so driving it around too much is probably not so smart. I ordered a new airfilter, never changed that in all the years I have had it. I ordered a new fuel filter too, thinking that maybe the car is struggling at low RPM getting fuel or air enough?
I have not had any check-engine light pop up ever (yes, the light works!), but would the ECU not let me know if the cats were failing? If one of the O2 sensors was not working well?
I tried using this Durametric to see if there was really something failing that I could not see with the regular OBDII sensors, but found nothing.
I tried plotting the O2 sensors, but didn't really see anything wrong with them.

I am waiting for the temperature to drop a bit here, if I want to wait until it is wet and damp, I guess I will be lucky to smog it this year...

Does anyone have any suggestions to how to get this NOx number lower? What can I try to check at home by myself? If it does not pass this week, I guess I will drop it off at the local mechanic and have him diagnose the problem.
Yes, I guess new catalytic converters would most probably take care of the problem, but they are a fortune. Also, I am not sure that ones I have are actually bad, as the sensors to measure if it is working, could also be bad.

What puzzles me is why the system fails at 15mph, but passes with flying colors at 25mph. It is only 200 RPM more...

 

Find some good used cats... yours sound worn out. If your check engine light works, then the engine is controlling everything properly. An O2 sensor does not measure NOx levels, so if the cat has lost its functionality in that regard, your OBDII system won't warn you of an issue. But the Smog Check will.

About Arco fuel: my smog shop has a list from the state of CA that lists common causes of a failed Smog Check; handwritten in the #1 slot for failed checks is Arco Gas.

 

I can't believe that you're at 655ppm at 15MPH and 1563 revs, and at 15ppm at 25 MPH and 1765 revs. That seems too great a disparity.

I'd guess bad cats would affect both values equally.

 

Here is the stuff that I used...."CRC Guaranteed to Pass". It saved me a ton of money and zeroed my emissions. Everyone in my family now uses it and the results are amazing. If you look at the mods on my car, you will see that I have lots of reasons not to pass smog in CA. I recently failed again on the visual inspection....I have to get a stock air box, headers, and photograph the CARB exemption number on my high flow cats in order to pass...what a pain. My wife and I plan on moving to another state to permanently solve the problem. If you look up my "failed CA smog post" you will see that my issues were similar to yours, except my car is not stock. Good luck.

 

How long didmyou drive it before the test. Need to get those cats good and hot. Drive it like you stole it right up to the test. Run through the gas you have and get some good stuff in the tank. Even some 93 if you can find some.

 

Ha, moving out of state because your emission tests fail? That seems a little extreme to me :-)


After a few months of just standing around, I guess the gas must have gone bad, maybe there was some water in it? Refilling with Arco was probably asking for trouble, even though they try hard to convince people they are selling Premium grade gas. I usually fill up my old clunker there, but never my 996, I was just not thinking clearly...


After I failed, I tried to add this Techron to the remainder of the Arco gas tank. I drove it till it was almost empty, filled up with another Techron and a full tank of Chevron 91. Then I drove it around for a while again, a long trip 250 miles. Filled up again at Chevron and the morning I was doing the smog test I added this Lucas Oil treatment that promised to reduce the NOx.
I was driving for about 20min before the test, it was running in idle for about 45min while waiting for the other customer to finish. That should make it warm enough, right?
Well, something changed for sure compared to the previous smog test, but I am not sure what made the difference.


The smog guy only put one sensor up the left exhaust. I am not sure what the other exhaust would show.


It is easy to say that the cats don't work, but I am not so sure. If both numbers had been through the roof, OK, but they are not.

I just changed the air and gasoline filter, I will try to empty the gas tank.


If I drive it like I stole it, I might attract too much attention, running on tags from June :-(


Looks like it is time to try the Guaranteed to Pass juice. Actually I looked at the bottle, but put it back on the shelf - I was sure it was just some BS they write to sell it, but sounds like it works...?

 

My family is moving out of state, after a lifetime in CA. The smog crap is only a minor contributing factor. I have gasoline running through my veins. A couple months ago I was about to buy a 1976 930, until I found out that the smog equipment had been removed and a later engine had been swapped. I spoke to a local expert who convinced me that getting it to pass smog in CA would be next to impossible, with a later 930 engine installed.
I previously bought a set of factory cats to get my car to pass smog. I sold them a week later. I drove to the smog shop with my rear bumper removed to make it easier to reinstall my high flow cats. The last time my car failed smog, I was looking at having to buy a new ECU from the dealer because my GIAC flash could not be returned to stock (per the company that flashed it). The Guaranteed to Pass juice saved me a ton of money and hassle. There was no other explanation for my emissions being reduced to almost zero. You will not regret it.

 

Only need to stay in lower gear to achieve same result. 3rd gear tops at highway speed..

 

If there is no hard fault, a DTC, related to converter problems (or O2 sensor problems) the odds are high the only problem is the car needs to be driven some.

My Boxster recently failed its SMOG test here in CA. I had taken all the precautions, well, I had driven the car enough to ensure the engine and exhaust was up to operating temperature and had been for some time. The day was warm, and I let the engine idle while I get the paperwork done.

After the test I swung by the dealer to consult with the techs. Both when asked said the same thing as I opened with above. If there are no error codes the car needs to be driven some. I headed out on the freeway and put around 40 to 50 miles on the car. While I did a few hard acceleration runs most of the time was spent just at highway speed. (In fact on the way home I had to follow a CHP cruiser.)

Back at the SMOG station I had the car in for a second test and it passed with no problems.

FWIW, I do not run Arco gas or any discount gas in my cars. While Arco and some other discount gasoline stations offer top tier gasoline I found with my Boxster and its sensitive converter it would trip and error code more often than when running Shell gasoline. So, I run either Shell or Chevron where i live and drive and on the open highway try to use Chevron or Shell, but Unocal and Philips 66 seem to work just fine, too.

BTW, Chevron, I read somewhere, is what Porsche uses for the official emissions/mileage tests here in the USA.

My advice is be sure the plugs are reasonably fresh.

I note you have changed the air filter which is good.

Before the test arrange a 40 mile drive say 20 miles down the freeway and then back again. Try to pick a day and time when the SMOG test facility is not busy so you can get the car in pronto. On the day of my Boxster's test my usual SMOG station was busy and I was directed to its other facility which was not busy.

Note the addresses of several facilities in your area so if one is busy you can drive over to another one until you get to one that can take your car in right away.

 

The last few nights I spent on changing a few things:
- air filter
- fuel filter
- topped off the coolant (2 liters missing???)
- topped off the oil, 1 quart
- changed the spark plugs (actually pretty easy)
I drove around with 2 bottles of Techron, 1 bottle of Lucas Engine cleaner something and finally a bottle of the Guaranteed to Pass juice.
Sunday I took a joy ride from San Diego to Palm Springs and back to let the additive do its work. In Palm Springs and 105 degrees I was reminded that my AC doesn't work. Arghhh

Anyway, I took an hour detour home today to make the car warm, then went for a retest:



Happy ending! :-) I don't know exactly what made it pass, but to be honest, the other 2 results look very fishy.

I just wanted to thank all of you for the advice and support, it helped for sure.

Now I just have to figure out what to do with the 2 used cats I got my hands on in the midst of the stress, haha

 

Congrats on finally passing. I bought a set of stock cats before I discovered the additive. I sold them here for what I paid for them...minus shipping.