Nissan Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter #1
I have owned this Xterra sense 2000 I have had no problems with it other than it only was getting 12 mpg. now it is slowly getting worse. it has a 3.3 V6 supercharged. could it be the fuel injectors? It has around 250.000 miles on it. Not sure where to start. I've checked for leaks and found nothing.
Any advice???
 

·
NF Mod/Nissan Master Tech
2006 Pathfinder LE, 2003 Frontier SVE
Joined
·
10,036 Posts
You've had a 2002 Xterra since 2000?? I'll assume that's a mis-type! ;) I have a 2003 Frontier SVE 4x4 that has the VG33ER engine, as well, and about 210,000 miles. 12-13 MPG combined seems about right on premium. If the fuel mileage is getting worse, that could be any of a number of things. First and easiest is to make sure the engine's ignition system is not in need of a tune-up. As you probably already know, it's best to stick with OE parts, like NGK plugs and wires and Nissan cap and rotor. Get a fuel pressure tester and test the fuel pressure and do a fuel pressure leak down test. I'm not so much worried about too little fuel pressure as your gas mileage is dropping, but, too high fuel pressure, which would cause it to run rich and burn more fuel. You should see 34-36 PSI with the engine running and around 44-46 PSI static fuel pressure. If the fuel pressure is too high, most likely the fuel pressure regulator is shot. Also, pull the vacuum hose off of the pressure regulator and make sure there's no gas in it, which would indicate the diaphragm is leaking. A leak down test would show if one or more of the fuel injectors is leaking. When I purchased mine, I had a bad fuel injector that wasn't injecting fuel. With 184,000 miles and at a time when I just purchased it and was doing a number of repairs to put it safely on the road, I decided to just bite the bullet and replace all of them with remanufactured fuel injectors and a new pressure regulator. With close to 200,000 miles, those injectors served their purpose, IMO. The front, or "upstream," oxygen sensors are also something to look at, especially if they are original. Over time, they can lose their efficiency and they are a main input for the ECM to determine how much fuel the engine needs. If you had a scan tool, you could monitor their activity. If you need new sensors, stick with NTK or Denso brand; Rockauto usually has the best prices. Note that the rear sensors are only used to monitor the converter efficiency and don't effect the fuel management. Get some MAS cleaner and carefully spray clean the hotwire in the mass air flow sensor. You can check the resistance of the ambient air temp sensor to make sure that is good; online factory service manuals are available for free at Nico Club's website. If that doesn't fix the fuel mileage issue, check for cracks in the manifold near the oxygen sensor and check the engine compression and compare it to manufacturer specs. A cylinder leak down tester can check the ability of the rings and valves to seal the cylinders properly. An exhaust back pressure test can check to see if there is any exhaust restriction. If you don't have any of these testers, many are usually available through tool loaner programs at auto parts stores like Autozone and Advanced Auto Parts.
 

·
Registered
2003 Nissan frontier XE D22
Joined
·
108 Posts
The fuel pressure regulator might be at fault. Also it might be time for a tune-up, change spark plugs, wires,cap,rotor,pcv and timing belt with genuine Nissan OEM parts. Look out for restrictive exhaust catalytic convertor and leaky valve stem seal. Get a scan tool and look at the STFT...SHORT TERM FUEL TRIM when the engine is hot, place the transmission in drive and hold the brakes. Look at the short term fuel trim should read close to 0%. If it above on the + side its a rich condition. If its in the - side its a lean condition.
 
1 - 3 of 3 Posts
Top