Excessive Oxides of Nitrogen (NOx)

1. Blocked, leaking, or improperly routed vacuum lines.
2. Incorrect EGR system operation.
3. Obstructed EGR passages.
4. Inoperative BVSV.
5. Lead contamination of catalytic converter.
a. Check for absence of fuel tank filler restricter.
6. Faulty feedback system.