Barely passing smog

[tmblackflag]

My car has barely passed smog since i purchased it some 6 years ago. I have all records and it looks like the only thing that was changed was an O2 sensor a while back.

Looking at my results (hyperlink below) is there any common knowledge on what needs changed? Cat converter? O2 sensor again?

I should note that when the car starts, for the first 1-2 minutes it smells like exhaust. This persisted even after the top end was rebuilt about 10-15k miles ago.


https://imgur.com/a/tR7dL

['76 911S 3.0]

High NOx is indicative of high combustion chamber temps or a failing catalytic converter. Based on the CO and HC numbers, I'd say the engine seems to be running pretty well. The NOx bed is separate from the CO and HC bed,and can fail independently of one another.

[tmblackflag]

The top end was done after the smog i posted and engine runs even better but the NOx numbers are similar. So you're saying a new cat is likely the culprit? Does that jive with the smelly exhaust on startup symptom?

[bemmett]

I failed due to NO up here in the SF area. Your NO readings are worse than mine, but everything else looked reasonably similar prior to my failure a year ago.

A new cat (220K on the original) basically cleaned it all up: NO, HC and CO all look really good now.

Original Cat


New Cat

[Nick Triesch]

You barely passed smog? Are you kidding?????congratulations! You passed!!!!!!!! You should be dancing in the street!

[tmblackflag]

Smog is due mid-may and you can see my NO numbers are ridiculously close to failing. I'm just trying to get ahead of the problem and hope the exhaust smelling on startup for the first 1-2 minutes goes away at the same time.

[Nick Triesch]

I was just having fun. I’m glad you passed. I just failed a few weeks ago but a complete tuneup with a new 02 sensor and 40 pounds of air in the back tires and I passed!

[tdw28210]

Is 1975 (and newer) the cut off year for Cali smog tests? You guys out there have my sympathies. Fortunately, the Porsche bug didn't bite me until after I left San Mateo for the East Coast.

[Tippy]

Do you run the crap out of it to get the engine nice and toasty before testing?

[bemmett]

Originally Posted by tmblackflag

Smog is due mid-may and you can see my NO numbers are ridiculously close to failing. I'm just trying to get ahead of the problem and hope the exhaust smelling on startup for the first 1-2 minutes goes away at the same time.

I had similar startup combustion smells prior to replacing my cat, and they're all gone now. After 220K on the original, all the catalyst had basically disintegrated.

[Jack Stands]

I think 1976 is the first year for California testing. Here in Illinois they go back to 1996 (when OBD2 came on board) and just plug into the computer port. No sniffers required.

[86 911 Targa]

My approach to the test is to disconnect the oil cooler fan
which activates at 210f, and run the oil temp up to about
230f during a "spirited" freeway drive.

Then, leave the car running until the very begining of
the test.

Best,

Gerry

[darkbeer]

This is a re-run of my experience last month to pass smog. Also NO was just barely to high "FAIL".
I went ahead and bought a new, quality, CAT, and passed with near zero's, across the board. Now, coughing up $800 every few years for a CAT, (they don't last like the 'original' ones) is awfully expensive. CAT bypass anyone, and save the CAT for every 2 years test ????

[tmblackflag]

Dang darkbeer that sucks. How long do they last? just got mine back today and will get smogged this weekend.