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Old 09-30-2009, 10:17 PM   #1
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Default Helpéadvice on helping my Miata pass failed emissions

Hey guys,

My wife's 90 with ~298000kms just failed emissions today.

I am looking for some tips to help pass.
I can probably grab a good used Cat from work to help pass but I am hoping to just tweek a few things to pass...

curb idle test

limit / reading
hc 200 81 pass
co 1.00 0.15 pass
no n/a n/a pass

speed test

limit / reading
hc 78 83 FAIL
co 0.44 0.30 pass
no 907 798 pass

What do you guys suggest to help pass the HC test?

Thanks for the help!
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Old 09-30-2009, 10:27 PM   #2
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There's no way to adjust fuel, and from your other readings it's obvious that the O2 sensor is working.

All else being equal, retarding the ignition timing will decrease HC emissions somewhat.

Try dialing it back by 5 degrees (from wherever it is now) at idle with the TEN-GND jumper set. Some experimentation may be necessary, as all else being equal, retarding the spark will decrease HC and NOx, but slightly increase CO.




If you want some in-depth data, here's a good source: http://dspace.mit.edu/bitstream/hand...pdf?sequence=1 (timing vs. HC starts on page 53.)
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Old 10-01-2009, 10:50 PM   #3
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Thanks for the help Joe,

I think I will retard the timing to 5' and see what happens - i am pretty sure it is set to 10' or 12' now.

I guess I'll also check the air filter and plugs.

I changed the oil last week and have been running high test too.

If it still fails I may reinstall the old exhaust back onto the car which has a newer cat on it.

Thanks.
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Old 10-01-2009, 11:00 PM   #4
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run low octane fuel for the sniff test. you barely failed, which may have been due to the high test.
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Old 10-01-2009, 11:11 PM   #5
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Quote:
Originally Posted by Ben View Post
run low octane fuel for the sniff test. you barely failed, which may have been due to the high test.
Hey Ben ,

I was running low octane before and for the test, I just put high test in now, after the test.
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Old 10-01-2009, 11:19 PM   #6
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okee dokee, well burn through the tank and refill with regular before the re-test.
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