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  #1  
Old 02-28-2014, 02:50 PM
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Nox readings in emissions

What causes bad NOX readings in an emissions test?

- Peter.

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Old 02-28-2014, 02:53 PM
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lean mixtures, timing off, egr valve stuck open
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Old 02-28-2014, 02:57 PM
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Had that problem on my Landcruiser recently. Non-operating EGR. The EGR exists to reduce NOx emissions by lowering combustion temperatures. I troubleshot mine with a Mity Vac. What kind of car? Mine had a bad EGR valve, a bad modulator and a bad vacuum solenoid valve. You can pass emissions by forcing the EGR to be on all the time. I did that because the VSV which controls the on/off of a Landcruiser EGR had not arrived before I had to take my free follow up test.
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Old 02-28-2014, 02:58 PM
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High NOX comes from higher combustion temps. It is tougher to clean up so automakers tend to run a bit rich (which lowers temps) and just clean up the HC in the cat. Egr is supposed to lower NOX by "poisoning" the mixture and making it burn at a lower temp. EGR could be stuck closed or just clogged. i think early timing can up the temps too. of course a bad OX sensor will screw it up too. If you are lucky, you have the cheaper of the two models; usually with just one wire.
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Old 02-28-2014, 03:40 PM
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If you have OBD, start with codes. If not, always start with the EGR when troubleshooting a NOx issue.
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Old 02-28-2014, 11:54 PM
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Thanks for the replies. It's a 1990 Suburban I am considering. It passed it's emissions recently in all areas but the NOX just squeaked by. So I'm wondering how much of an issue it could be in the future.

- Peter.
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81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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Old 03-01-2014, 12:14 AM
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Quote:
Originally Posted by pj67coll View Post
Thanks for the replies. It's a 1990 Suburban I am considering. It passed it's emissions recently in all areas but the NOX just squeaked by. So I'm wondering how much of an issue it could be in the future.

- Peter.
5.7L came with no air pump 89-91, so that might be the design value. Squeak = pass
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Old 03-01-2014, 05:31 AM
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You passed so you're good. If it doesn't pass next time, look at the EGR.
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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 362,xxx miles
08 Triumph Street Triple 30,xxx miles, lowered 10mm in front, Pirelli Angel GT tires, EBC HH brake pads, otherwise stock.
88 Jaguar XJS V12 92,xxx miles. I should be in the garage now.
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Old 03-01-2014, 12:59 PM
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Quote:
Originally Posted by INSIDIOUS View Post
5.7L came with no air pump 89-91, so that might be the design value. Squeak = pass
Interesting. I'm thinking the earlier, the simpler the better.

- Peter.

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81 240D stick. 316000 miles at purchase. 342000 now
2000 GMC Sonoma
Formerly...
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles. Deceased Jan 08
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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