Originally Posted by 92ranger lady
Hey ...does anyone know why my 92 Ranger would fail the low speed emission testing in the Nox (ppm) with a reading of 2794?? the hi speed reading passed @1116?? Just last June 2004 my truck failed and I had the catylitic converter replaced and asstd. other fuel cleaning stuff for around $500.00!! I hardly drive this truck only once a week for a couple of hours!! HELP???
Hi, welcome
Agreed, NOX increases when the combustion chamber temp rises above approx 2500F. It is at it's highest at part throttle with a light load which is exactly what the higher speed test is.
Typically it means that the EGR, or the hose connecting to the EGR is plugged. THat is both the most likely cause and the cheapest to fix. The EGR's primary function is to cool combustion temp's by feeding spent gases back into the chamber.
Advanced timing will raise combustion temps but most vehicles from mid 90's on won't allow you to alter the timing much if at all so it's not usually the cause for them.
Next likely is the Cat convertor but it is very unlikely in your case as you just changed it a bit ago.
good luck
Steve