If the vehicle is hard to start after setting overnight, the problem could be the fuel pressure regulator has failed and is allowing the fuel pressure to bleed off. A failed fuel pressure regulator will should be replaced.Google+
Car Problem Reports
Nissan Sentra Fuel Pressure Regulator May Bleed Off Pressure Overnight
Nissan Sentra Problem
Engines Affected: 1.8L 4 Cylinder, 2.5L 4 Cylinder
Average Mileage: 90,821 mi (26,000 mi - 210,000 mi)
Visitor, 2002 Nissan Sentra, 1.8L 4 Cylinder, 210,000 mi
After sitting overnight engine floods and will not crank without removing plugs and drying them, this only happens once or twice a week. Also using excessive gas.
Visitor, 2003 Nissan Sentra, 1.8L 4 Cylinder, 110,700 mi
I have to crank the car 2-4 times before the car starts.
Visitor, 2004 Nissan Sentra, 1.8L 4 Cylinder, 75,000 mi
engine hesitates to crank or takes to many turns to start the car. Once you drive the car come back and let it sit, try to start it again and it takes a few times before it does decide to start
Visitor, 2002 Nissan Sentra, 1.8L 4 Cylinder, 180,000 mi
Wont hold fuel presure
Visitor, 2004 Nissan Sentra, 1.8L 4 Cylinder, 82,000 mi
Long cranking before start.
Visitor, 2004 Nissan Sentra, 1.8L 4 Cylinder, 130,000 mi
had the pressure tested due to the fact the engine will not start right away its over 800.00 to replace
Visitor, 2006 Nissan Sentra, 1.8L 4 Cylinder, 88,000 mi
Same as above. When letting the car sit for any length of time, it will turn over for several seconds before starting.
Visitor, 2005 Nissan Sentra, 1.8L 4 Cylinder
Has a veryhard time starting, specially after a couple days parked.I removed air cleaner intake,filter is new.Engine sounds like it wants to start,but takes a long time.Finally fires.
Visitor, 2003 Nissan Sentra, 1.8L 4 Cylinder, 50,000 mi
Yep, won't start the first time but will on second or third try. Seems to be same problem of fuel bleed off. Haven't yet tried pump/regulator replacement or check valve fix. Nissan service bulletin NTB05-052a
Visitor, 2004 Nissan Sentra, 1.8L 4 Cylinder, 85,000 mi
I replaced the Fuel Pump Assembly with a genuine Nissan Fuel Pump Assembly--since it was significantly cheaper than the aftermarket one by Bosch. (The Bosch assembly also lacked the Fuel Tank Temp Sensor.)
The genuine Nissan part includes the fuel pressure regulator, fuel level sensor, fuel tank temp sensor fuel pump, etc.
Typically, dealer replacement parts contain modifications when known problems have arisen--like the fuel pressure bleed problem.