Assuming your Nissan Pickup truck's timing is incorrect and your Nissan is equipped with a 2.4 liter engine, ignition timing should be set at 10 BTDC (before top dead center). Timing should be taken from cylinder number one, while engine RPM is at 800, and with the throttle position sensor (TPS) electrical connector disconnected. If your Nissan is equipped with a 3.0 engine, the same procedure applies except timing should be set at 15 BTDC and while engine RPM is 750.
Find the timing marker on the crankshaft pulley and the second mark on the timing belt cover. Loosen the distributor tightening bolts. Using a timing gun adjust the ignition distributor to align the mark on the timing belt cover with the 10 BTDC mark on the pulley. Once achieved tightened the distributor and reconnect the TPS connecter.
(We recommend attempting to perform this task only if you have automotive mechanical experience.)
Correcting your Nissan Truck's ignition timing may very well lower CO (along with HC and NOx) and allow your Nissan pickup to pass the smog check.
