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A couple days ago I took my Trooper, 2.6 engine, in for a smog check, here in California. The numbers were all well within tolerance except the NOX, which was just a bit high--nothing outrageous but enough that it did not pass.

The normal cause for high NOX numbers is the EGR Valve. I've had very little experience with EGR valves, and none of it good.

I pulled the codes when I got home, and the only code which appeared concerned the O2 sensor. That O2 sensor was changed about 22000 miles ago, so should be good for anoth 68000 miles (I think they're on a 90,000 mile cycle, aren't they?). The Trooper is an '89, has 202,000 miles. Will a bad O2 sensor effect the NOX numbers?

On the other hand, would it help if I remove and clean the EGR valve? If cleaning would help, what is the proper way to remove the EGR valve?

Any other suggestions? Help is always appreciated. TIA

Ken
 

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A bad O2 sensor will cause all sorts of issues with fuel mixture.

I can't explain the chemistry behind it, but I'm sure that if the fuel mixture is not right, then the NOX #'s are probably not going to be right.

It could be a bad contact if the sensor isn't bad. I had a little corrosion on an O2 sensor contact not so long ago. Cleaned it up and things were OK.
 

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yeah O2 sensors can through everything off. Check the contacts and what not. Then go back and get it retested. If that dosnt do it then its the egr. *** far as that goes, i think you can clean them whith solvant. Im not shure on this though, hopefully someone whith a little more knowledge on this will chime in.
 
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