The maximum allowed NOx parts per million is 1522. I had 2434. Anybody know of an obvious part to adjust/change to fix this? Or could it be a lot of different things. 87 245 with 271k miles. FWIW I have no idea when the O2 sensor was last changed.
--
It's Jim (in Hartford CT)

Jim,

I'm among those who benefitted from disconnecting the vacuum line, whose purpose is to tell the ECU how to refine that last little bit of emissions out of the exhaust. Unobstrusively plugging the vacuum line from the distributor brought me from well outside specs to well within them.

I later saw an article on O2 sensors that showed graphically just how radically NOX ppm rise when the the mixture goes just a little too lean, which was evidently happening in my case.

I take it that your CO and other emission readings were OK, as mine were, which would tend to support this guess.

Here in VA, you get a free emissions re-check if you go back to the same station within 28 days (You have to read the reject certificate to learn that, because no inspection station owner is about to bring to your attention a rule that is to your advantage).

If CT is similarly kind, you might give this quick, cheap fix a try without having to invest a new inspection fee.
--
jds

Jim,

There's been some NOX reduction advice here on the BB involving the removal of the vacuum line to the Ignition Control Unit. You might run a search here for those threads. As I recall Bricks with LH 2.2 fuel injection that had totally failed the NOX test passed, with flying colors after the ICU vacuum line was disconnected. I've never had to resort to this myself to pass emmissions but it's worth looking into. It may solve your problem. Overly advanced timing, high engine temps, vacuum leaks and bad cats can also cause your Brick to blow high NOX numbers. Good Luck sorting this out ...

Look for vacuum leaks or other causes of a lean running condition such as a leak of unmetered air between the AMM and the throttle body due to a bad hose. Perhaps a leaking manifold gasket.

Are you still running the original cat? Sometimes you have to bite the bullet and replace them. I have a 91 745Ti that ran good but failed on NOX readings here in Ohio. Finally replaced cat at which point it passed with very low NOX levels and ran even better. Good luck.

Randy

Thanks for the post Randy-

The cat is about a year old. But I've had an on going high idle issue that I haven't been fully able to resolve. This works right in with your idea of a leak in the intake system. I've looked for leaks before and haven't found anything though. What is the best way to do this?
--
It's Jim (in Hartford CT)

You may be able to pass the NOx test by plugging the vacuum line to your Volvo/Chrysler Ignition CU.

See my original post, with technical description here, and a success story here.
Others are shown here, and here.

--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

If you cat is only a year old, I would check the O2 sensor AND suspect the cat for premnature failure due to an improper running mixture. There may also be other things which lead the car to run high NOX (that number is really high!)but it usually means a bad cat deteriorated from a rich condition like a bad O2 sensor, not a lean condition. In your case, I would first check the O2 then the AMM, then the coolant temp sensor (driving the ECU to run over-rich condition).
Sometimes the inspection report gives an O2 reading. This number will tell if there may be leaks by high values. Anything over ~0.5% should be considered high.
When all is fixed, you may be lucky the cat still works.

You can remove the hose between the AMM and the throttle body and give it a good visual inspection.

People talk about using carb cleaner or an unlit propane torch to introduce a combustable around the intake manifold gasket and listen for an increased idle, but that always seemed risky to me.

I have also heard that an exhaust leak either at the manifold runners or a connection can create a lean running conditon.

Try doing a search for emissions or NOX. There have been a number of discussions on the subject.

Randy