You might want to do a general tune-up. Change the spark plugs and engine
oil. You also want to make sure there are no disconnected, loose or brittle
vacuum lines. A common fault of older vehicles failing the smog check is
broken or disconnected vacuum lines. Vacuum lines are usually thin and
exposed to high temperatures in the engine compartment. Soon as one is
dislodged or broken, unmetered air enters the intake manifold, disrupting
the air/fuel mixture. So just take a quick look under the hood. Make sure
everything looks intact... and do the tune up. Have the gas tank fuel 3/4 of
fresh fuel (manufacturer recommend octane), and ensure your Nissan is properly warmed up before the smog check.
posted by SmogTips Support
