CA Smog test blues with my Miata

Shentar

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Feb 3, 2006
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Location
San Francisco, CA
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06 Porsche Cayman S, 90 Miata
I'm super frustrated at this point. I've failed my 4th smog test.

I ran a smog test in April on the Miata. Its a 1990, so 1.6L engine. There is no EGR on these cars. Its got about 180k miles.

First test, I dropped the car off at a place 2 miles from work during my lunch break, in San Carlos, CA
Test results: https://lh5.googleusercontent.com/-7yzencBkR-g/Tj2qwYUuinI/AAAAAAAAAqw/RU-_TIeb7u4/s800/photo.JPG
Failed due to high NOx.

I replaced the catalytic converter with a new Magnaflow, CARB legal 3-way catalytic converter. I also put on a Racing Beat intake with a K&N filter.The cat that was on there was the OEM one. The next test was done, again, on a lunch break, but it was about 8 miles from work, and I did a little driving before I went there.

Test 2 results: https://lh3.googleusercontent.com/-...kY/tcZm4xJwyiY/s800/photo%2520%25282%2529.JPG
Failed due to high NOx. Everything else came down so the new cat has helped.

The guy at the 2nd test place in Redwood City said it was running lean, hence the high NOx. I installed a new O2 sensor and new spark plugs. I retested a week later in Hayward. I did the test with 91 octane gas and I did a 50 minute hard drive on the freeway beforehand. I will say after the plugs, O2 sensor, intake, and cat, the car ran really strong.

Test3 results (one week after test2):
https://lh3.googleusercontent.com/-...kc/M_wmGZU2b4k/s800/photo%2520%25281%2529.JPG
Failed due to high NOx. This time I'm a gross polluter. Nice.

The tech checked my O2 sensor and MAF and said both were fine.
Time to get serious. I ran Seafoam in the car. I filled up with 87 octane gas and put a bottle of Seafoam in the tank. I put 8oz in the intake manifold through a vaccuum line, and 8oz in the crank case. Lots of white some from carbon burning. I had the oil changed the next day. I drove through that tank of gas, and refilled with Chevron 87 octane. I took off the aftermarket intake and put the OEM box back on. I checked the timing and saw that it was set to 16 degrees BTDC. 10 degrees is stock. I reset the timing to 8 degrees before BTDC. I did a 40 minute hard drive and took it back to the place in Hayward where test3 was done.

Test4: Failed due to high NOx. He didn't do the ciomplete test because it was reading too high right away. About 1700 NOx.

so. A little e85 in the gas tank? colder spark plugs?

EDIT: to provide more data of the history since I started trying to get it smogged.
 
Last edited:

JCE

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I know you put in a new cat but I would check for exhaust leaks and run Seafoam through you vaccuum lines.
 

Shentar

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06 Porsche Cayman S, 90 Miata
I know you put in a new cat but I would check for exhaust leaks and run Seafoam through you vaccuum lines.
I did the seafoam through the Vac lines. I made a more detailed post elsewhere, so I'll edit the original post.
 

Spectre

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Yank the fuel injectors and have them flow tested.
 

dtv70r

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SF
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90 Miata, 98 Volvo V70 T5 M
Hello, I found your post when doing research on my 1990 Miata CA smog hell. You have exactly listed my situation and I am wondering if you were able to get your car to pass smog. Any info would be much appreciated. Thanks.
 

Shentar

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Joined
Feb 3, 2006
Messages
1,603
Location
San Francisco, CA
Car(s)
06 Porsche Cayman S, 90 Miata
Hello, I found your post when doing research on my 1990 Miata CA smog hell. You have exactly listed my situation and I am wondering if you were able to get your car to pass smog. Any info would be much appreciated. Thanks.
I did figure it out. The main problem was a hole in the exhaust ahead of the catalytic converter. The guy at the shop that installed the catalytic converter had told me that I would always blow the gasket between the cat the downpipe because one side of the flange was new and straight while the other side had been heated up so much that it would be slightly curved. Sure enough, it was blowing the gasket. He put a new gasket on there and I drove the car to get it smogged before it blew. A month or two later, I went to replace the gasket with another one that I had lying around. I found that the nut the guy had used had some slag on it, and no washers were used. I replaced the bolts and nuts with new ones, as well as some washers for each side of the exhaust flanges. Thats kept it from leaking once they were good and torqued down.

Beyond that, I also had ended up changing the fuel filter, o2 sensor, spark plugs, and put the OEM intake back on it. Also, I retarted the timing to 8 degrees and ran 87 octane gas for the smog test. Lower octane gas will have less NOX in it that higher octane.

I'm about to have to resmog it again this month, so we will see how it goes. I'm going to try to just change the timing back down and leave the aftermarket intake on it to see how it does. Its not a hard job to change out the intake, but I'm inherently lazy, so the less I have to do, the better.
 
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