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Discussion Starter #1 (Edited)
Well, I took the LHS to the testing station Sat morning. She failed. Specifically, it was the NOx that failed, over TWICE the limit. The HC and CO were well below the limits. The general diagnostics that came with the results pointed to: lean air/fuel mix, EGR problems, cat. conv., and something else. (can't remember, the sheet's at home and I'm at work) So I looked at the EGR. It seems ok, tested it per the Haynes manual, took it off and cleaned it and the tubes. Then I checked the plugs. They're almost two years old (Autolites) when I put new wires in. The gap on them were close to .060 (I had gapped them @ .050, per the tag - I know there's a TSB, but I don't know if the computer's been updated, and there isn't any cold-start issues) So I put in some Champion coppers gapped @ .035 (I checked each one) and now am going to take it in after work today. If anyone had any similar experiences and what they did to fix it let me know. Otherwise, wish me luck.

Oh, I also did the SeaFoam thru the intake & in the tank. Smoke show city!

Thanks, Andrew

Forgot to add this: 95 LHS, 129K mi, 3.5L engine, timing & water pump @ 105K mi, plugs, wires, O2 sensors @ 106K mi, "new" tranny @ 119K mi, regular oil changes, no check engine light, daily driver (wife's car so I don't get much wheel time)
 

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EGR is one of the biggest culprits for increased NOx emissions. That's actually its purpose, to reduce combustion temps, which keeps down the NOx. Not sure on the air/fuel link. How old are the O2 sensors? They will lead to a/f mixture issues when they go bad.
 

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Discussion Starter #3
The O2 sensors were replaced about two years ago. They were replaced before the plug wires in an attempt to fix a misfire problem (that the plug wires were responsible for). I did notice that when I drove the car to the test station that the temp gauge was just under the halfway mark, and after I replaced the plugs the gauge was closer to the 1/4 mark. Maybe it'll pass as the temp was lower and high comb. temp increases NOx. I don't have a lot of $$ to throw at this problem, so I'm hoping it passes.

Andrew
 

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Discussion Starter #4
No Go. Failed even worse. NOx was higher. Guess I'll have to take it somewhere & get it checked out. Don't want to just throw parts at it. Let you know what fixes it.

Andrew
 

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Discussion Starter #5
Guess third time's the charm. This time they didn't have to run the whole test, it passed easily. Culprit: EGR solenoid. I'll make another thread about what was wrong with it and how I tested it. So relieved. Don't have to deal with that for another 2 years. Maybe I'll have a "new" 300 by then.

Later...Andrew
 
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