Have reviewed archive and gotten good ideas. Looking for latest feedback. Vehicle runs great. Maryland gives one figure per test, my vehicle: Hydrocarbons 17841 GPM Pass, Carbon Monoxide 51013 GPM Pass, Oxides of Nitrogen 45922 FAIL.
All emissions failures appear to be for NO2 on these vehicles. Have replaced the EGR with a fuctional one. "Engine check light" code also read that the throttle position sensor was off but Chilton manual says this is not an emissions issue and only effects the auto tranny which shifts fine. O2 sensor and cat could be replaced but these are after combustion components and may not be the cause. Engine check light goes off after a few miles but I still don't pass the test even with 20 minutes of freeway drive to get to the station. Nect idea,per archive search, is to pull the intake manifold and blast the EGR intake (not excited to do this). I have 30 days until suspension. All ideas welcome.

Per this reference, these are the likely culprits:

* Malfunctioning EGR valve

* Lean fuel mixture (AFR above 14.7, Lambda above 1.0)

* Improper spark advance

* Thermostatic air heater stuck in the heated air position

* Missing or damaged cold air duct

* Combustion chamber deposits

* Malfunctioning catalytic converter

Hope this helps.

Welcome to the Wire! <img src="/forums/images/graemlins/cheers.gif" alt="" />

My NO went to almost 0 with a new cat <img src="/forums/images/graemlins/kewl.gif" alt="" />

You still need to check everything first as it could be a host of issues.

<img src="/forums/images/graemlins/patriot.gif" alt="" />

How is your cooling system? These things are prone to trouble in that area (fan clutch?), and that can cause NOx levels to get up there. NOx only becomes a problem once the combustion temp. gets above 2500 degrees f. which can be caused by overheating. You may also try getting rid of some carbon buildup in your combuistion chambers which can cause "hot spots".

How do you know that the EGR is working? Open the EGR at idle. the engine should run rough or stall. If not, you have clogged passages. Check engine temperature and carbon build-up. Be sure the correct heat range spark plugs are installed. Most of Nox has to be controlled at the engine. The reduction bed of the catalytic converor is limited as far as NOX conversion.
Conner

My 89 3L failed the NO2 last year. Fault was a failed relay. Sorry, I'm a long way from my car and receipt until mid July. All I remember was it was easy to replace and it was on the left inside fender. The relay is no longer manufactured and not stocked. I found a specialty shop in CA that stocks hard to find emissions parts. $65 later I was back in business and it runs okay on regular instead of the 89 octane. I was told I'll fail the next one because of the cc. Aftermarket ccs are good for 2 years only apparently.

Real simple and works every time.
1 gallon denatured alcohol to 5 gallons of gas.
Then when passed test fill up tank.