smog fail on NO

1991 ISUZU TROOPER
90,467 MILES
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[email protected]
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would not pass smog I ended up replacing headgasket, valve job, valve lashcomplete tune up, all new vacuum lines and pcv, sensors ect. It still failed just barely, it failed NO
max is 704 @ 15 mph it measured 854
max is 606 @ 25 mph it measured 638
tech checked egr working fine
tech suggested changing timing from 13 degrees to 9 degrees
Any Ideas?
Feb 21, 2012 at 12:47 AM
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RASMATAZ
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Check the EGR valve, a problem with it will caused the Nox -oxides of nitrogen to go high due to excessive combustion temperature
Feb 21, 2012 at 12:51 AM
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[email protected]
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The tech checked it out using a vacuum pump/gauge said it was working
Feb 21, 2012 at 1:15 AM
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RASMATAZ
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Tell him check the catalytic converter, oxygen and coolant temperature sensors-
Feb 21, 2012 at 1:29 AM