There are several reasons your Nissan Quest could have produced high NOx emissions. The most common is a malfunctioning EGR system. The EGR valve is used to cool down combustion chamber temperatures by delivering inert gas to the air/fuel mixture. NOx emissions are formed when engine chamber temperatures rise above 2500* F.
Your Nissan Quest's EGR valve should be inspected for proper operation. A working valve should be able to open its passage using manifold vacuum. The EGR system is prone to collecting carbon build-up. Since the EGR valve pulls exhaust gasses from your Nissan's exhaust and introduces them back into your engine's intake, over time the EGR passages may become plugged with carbon deposits. It is important to ensure once the EGR valve is opened during idle the engine RPM decreases almost to where the engine is about to stall.
Other faults which may cause your Nissan Quest to fail the smog check for high NOx are:
Bad Engine Cooling - If your Nissan's cooling system is not working efficiently, chances are there is an excessive amount of NOx being created. For this reason you want to make sure your Quest's temperature gauge is always normal and that your cooling system is working properly.
High Cylinder Compression - Carbon build-up within your Nissan's combustion chambers will cause increased engine temperature and high NOx. An increase in carbon build-up causes increased cylinder compression, which causes high temperatures, which result in high NOx emissions.
Lean Fuel Mixtures - Lean fuel mixtures cause high NOx as well. A lean fuel mixture is when the engine receives less fuel then is necessary to obtain efficient combustion. Lean fuel mixtures can be caused by vacuum leaks. Vacuum leaks will allow the suction of un-metered air into the combustion mixture or exhaust (depending on where the vacuum leak is located) disturbing pre/post fuel combustion and increasing NOx emissions.
posted by SmogTips Support
