Emissions tests

[steve t]

The car is an 87 gw that is stock, and has 88k miles. It failed the emissions test here in dc, which is pretty tough - they don't just measure idle levels, but use a dynamometer type setup. HC was 1.337, under the standard of 3.2, CO was 15.274, under the standard of 80, but NOx was 8.677, over the standard of 7.0. The carb and egr valve were replaced less than 5000 miles ago, and the timing was just set at 12 btc, but the catalyst was orig and pretty sorry looking, so I had it replaced. But the car failed again on NOx! They do pass you if you have spent more then $450, and although I was only out $290 they passed me, but I wonder where these "standards" come from? Could this car ever meet the standards? I'd rather not spend a bunch of money for nothing next time. Does anyone know if AMC put out figures for this car's pollutants in 87? I'm presuming the figures are grams per mile or something like that.

Thanks for any help you can give on this

[chrisnsarah]

In CA, it's figures in PPM,(parts per million). I don't know how they get these figures, either form the manufacturer or from the air resources board testing. The usual cause of high NOx is a lean fuel mixture that raises the cumbustion temps. The egr is supposed to help reduce the NOx, you said you replaced it but there are different sized orifices, so hopefully you have the right one. And yes, the converter removes even more NOx. they haven't started dynometer testng where I'm at yet. Can't do it anyway with a Quadratrac. I just make sure I do a good tune-up, new plugs, wires, cap, and rotor. and do a quick carb adjust, and I pass. Rig's are '75's, no converters.

[DjD]

High NOx is most likely related to the EGR. My EGR worked fine when connected to a hand vac pump but found out it wasn't getting vac when connected to the engine vac hose. Are you sure there is vacumm in the hose running to the EGR after the engine is warmed up?

[nograin]

Here were my results.
Amen to the suggestions about vacuum operating everything OK. EGR dilution is needed for the running test.
http://www.ifsja.org/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=2&t=006744

Search seems to be working. If you are curious you will find many other posts for comparrisons.

http://www.ifsja.org/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=2&t=004404