The fuel injectors can fail and cause drivability problems. Often there is no Check Engine light and the failures can be caused by corrosion of the connector, clogging beyond the point of cleaning, and/or internal failures.Google+
Car Problem Reports
Nissan Xterra Fuel Injectors May Fail and Cause Drivability Concerns
Nissan Xterra Problem
Engines Affected: 3.3L V6, V6
Average Mileage: 109,935 mi (15,045 mi - 178,880 mi)
Visitor, 2001 Nissan Xterra, 3.3L V6, 178,880 mi
Same problem an that's just one of many
Visitor, 2000 Nissan Xterra, 3.3L V6, 160,000 mi
Not fixed yet. Misfire on Cyl 4
Visitor, 2004 Nissan Xterra, V6, 45,750 mi
Problem with fuel injectors. Engine light did come on. Luckily covered under warranty.
Still is not repaired correctly. 2 years now - emissions problems. Have had an oxygen sensor replaced, all spark plugs replaced, numerous other things (hoses, belts, timing belt, radiator, power steering, center link and idler arm) just to name a few! I need help. Auto Zone codes say Knock sensor or misfire # 4 cylinder or Catalyst system efficiency below threshold. But mechanics can't seem to fix it and keep the check engine light off more than a week. It runs a little better with a full tank of high octane gas.