Originally posted by dmorris1200
A NOX failure is often caused by a faulty EGR (not opening or clogged passage) but because of the opposite reason Jmark gave. (HuH?)
NOX failures mean that the combustion temps are too high. This is caused by lean mixtures.
Don't know where the confusion came from in my previous post, but I"ll re-write my first sentence.
"As far as the "high CO failure" goes, You could try leaning the idle mix a little and make sure the air cleaner and pcv valve are good.
Seems to me that if he is failing because of "high CO", its not lean. An in-operative EGR will cause combustion temps to rise ( because the engines are designed to run super lean anyway) and increase NOX readings. The main purpose of the EGR is to cool the combustion temps to keep NOX down.
As far as leaving the pcv laying on the valve cover sucking fresh air, thats an automatic failure here is AZ, no questions asked, your done, see ya tomorrow.
Leave out the air cleaner, same thing.
Un-hook the advance, same thing.