Quote:
Originally Posted by SeanPlunk
What would cause a 4cyl Jeep to pass HC, and CO with flying colors, but fail NO at 15mph but not at 25mph. Any ideas? It has a brand new cat (smog legal) that is clearly working for the most part. Help  |
Assuming the engine is otherwise workign to spec, the system is correctly metering emissions, that is clearly a failure of the reduction catalyst stage. I don't think there's any real break in period for a cat and I can't imagine it was a failure in manufacturing. Was the cat hot? It's always best to get a system good and warm before testing for emissions.
NO is (to my knowledge) only formed from high combustion tempratures. This can happen for a variety of reasons. The top two that come to mind are a failing EGR (which lowers charge temps) or if there's a ton of carbon buildup in the cylinders that can cause some high residiual heat.