Cadillac Repair: 1995 Cadillac Deville emission failure on nitrus oxide, combustion chambers, oxygen sensors

Question
I recently purchased this vehicle and have taken it through the Az emission test several times. It has failed the NOX test with readings at 2.26 woth a 2.00 threashold. I had the oxygen sensors replaced, but that did not fix the problem. Any suggestions?

Answer
Mark,
NOx failures are generally due to an EGR system failure of some type. NOx is caused by high combustion chamber temps, and they can be caused by several things:
1. EGR failure
2. Cooling system problem
3. Improper spark timing
4. Excessively lean A/F ratio
Get the picture? These are a starting place for you. You might also want to run a can of "Top-Engine-Cleaner" through the engine as a means to remove excess carbon from the combustion chambers.