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Old 08-27-2004, 01:15 PM   #1
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Default Failed NOx Help?

Went to inspection, here is the reading

Gas Standard/ Reading/ Result
NOx 853----1115----- Failed
HC 114 ----- 4 ------- Pass
CO% 0.63 -----0.00 ---- Pass
CO2% 14.4
O2% 0.2

Looking online says possible lean condition, running hot. I didnt have the car running too long and had a little bit above 1/4 tank in it, the temp was right below the 200 mark. Any one have any help or suggestions? Did a full tune-up to it a few months ago, except for the O2 sensor, that from what I understand would effect HC, but ordered one from GM and will put it in when it arrives anyways. I am off by 262, is that a high reading or is it low? ANY HELP would be great. In NJ, not sure if this Failed the Idle or Dyno test, they do both here. Thanks
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Old 08-27-2004, 01:32 PM   #2
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Yes, your NOx is too high. Could be the oxygen sensor, or possibly problems with the EGR valve. Do you have a service engine soon light? You might want to retrieve the codes anyway.
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Old 08-27-2004, 01:48 PM   #3
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No light, but going to swing by Auto Zone to check anyways. Any other suggestions?

Oh yeah, I realize its too high, just meant is that really high or is it only a little high, should have been more clear, thanks!

Just realized I ordered the wrong O2sensor from GMpartsdirect, 10 minutes after I ordered it. Found out I have the 3 wire sensor, hopefully they will change it over for me, even though on the site they say they wont...
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Old 08-27-2004, 02:32 PM   #4
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Possible catalytic converter, it is the last fuction in the emission process, especially when all of the other readings are well below normal, its primary funtion is to lower the NOx (Oxides of nitrogen).

Oxides - A binary compound of an element or radical with oxygen.

Nitrogen - A nonmetallic element that constitutes nearly four-fifths of the air by volume, occurring as a colorless, odorless, almost inert diatomic gas, N2, in various minerals and in all proteins and used in a wide variety of important manufactures, including ammonia, nitric acid, TNT, and fertilizers. Atomic number 7; atomic weight 14.0067; melting point -209.86C; boiling point -195.8C; valence 3, 5
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Old 08-27-2004, 03:02 PM   #5
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Just got back from Auto Zone and Advanced, they only had OBD II, not1I so I am going to try the paper clip thing. Got to go to Midas in the morning to get an exhaust leak checked out, Ill have them do the Cat test also, anyone know if and how much they should charge to diagnose the Cat? Thanks!
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Old 08-27-2004, 03:23 PM   #6
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Checked the PCM with the paper clip trick, only showing code 12, If there was a problem with the EGR valve, will the SES light store a code on a 93, its OBDI, I know its not as complex as II? Hopefully I will find out about the cat in the morning when I get the leak fixed. Thanks for all the help!

edit: Also changed out the PCV valve today, the other thing I didnt do on the tune-up. The o-ring that goes on the valve was really low and covered in oil, wiped it off and put it back on. I dont think that affects NOx but decided to do it anyways. Unless the lady (original owner) had everything serviced at the dealer, dont think anything really has been changed except oil. Everything I changed looked old and was original equipment, the PVC valve,the spark plug wires were still numbered from the factory and all nicely loomed, and the spark plugs had a diferent part number than the ones I had, I put OE Delco back in, maybe they changed the numbers since 1993? So I doubt the O2 sensor was changed, the car had only 60XXXmiles when I bought it, but it was still over a decade old.
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Old 08-27-2004, 06:38 PM   #7
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In March, my car failed, too, on the first try. I think it was NOx being too high. I filled up with good gas, took it on the highway for 15-20 minutes and then got it tested. It passed. While good maintenance is important, never underestimate the importance of having the car, especially cat, fully hot before testing. In Ontario, the re-test charge is only $17.50 so I was willing to take a chance before starting to change parts.
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Old 08-27-2004, 07:08 PM   #8
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In jersey inspection is covered when you register the car, so Ill get the leak fixed, change out the O2 sensor since its already on order and find out how much they want to charge for the cat test if its free or not much Ill let em do it, then try running it through again. Hopefully that will get me a sticker. Past 2 cars Ive had Ive been running without a valid sticker for almost 3yrs now, ticket is $124, so want to get this car passed before that happens, figure my luck on not getting pulled over might be running out.
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Old 08-27-2004, 09:29 PM   #9
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I looked around a little and according to a number of places higher combustion chamber temperatures raise the nox. Since the EGR actually lowers peak temperatures it combats nox. BUT this can also aparently be caused by a lean condition caused by any number of sensors or fuel related parts. You may want to get a multimeter and spend an hour testing all the sensors you can get your hands on.

Testing your EGR is pretty simple, I did it about a week ago.

Remove the wire clip going to it
The connectors on the EGR are arranged in a triangle and labled as such:

Top = A
Middle = B
Bottom left = C
Bottom right = D

Resistance should be:
A to B = 20 ohms
A to C = 10-17 ohms
A to D = 20-30 ohms

If those are ok take a 9v battery and connect the + to the A terminal. Then one by one put the negative on B C and D. You should hear a click on each of them as the pintle opens.

That whole thing should take like 10min and will at least rule out one sensor.
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Old 08-27-2004, 10:09 PM   #10
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Just to make sure, when testing the EGR, is this with the motor on or ignition on but no motor or nothing? Thanks, look forward to testing it tomorrow
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