1997 Pathfinder Bad Gas Mileage Help!!!

[kpuri]

1997 Pathfinder SEAutomatic Tranny102k Miles

Hello, I am stumped I was getting 10 mpg city and 12mpg highway.

I just recently did the following maintenance.New NGK Plugs (non platinum)Air FilterFuel FilterFront/Rear Diff. fluid changeTranny filter/Transfer case fluid changeOil change (5w30w)Checked Cap/Rotor and wires (no excessive wear noted)Checked tire pressureVisual check of fuel system no leaks notedRan scan on OBDII no stored or pending codes.

(I did have a intermittent P0440 code 6 months ago, so I purchased a new gas cap and made sure it clicks at least twice every fill up

After the tune up mileage has increased to 14.2 mpg (75% city 25% highway) I still feel something is wrong (driving habits ok could be a little better)

I tracked my Mileage on a 240 all Highway trip and got 15.4 mpg that was when the vehicle had about 80K miles on it, does that sound about right?

I was doing some research and comparisons and estimated my mileage should about 14/15 city and 18/19 Highway.The vehicle runs great and idles smooth.Not sure what to check next?I plan on testing my pre-cat 02 sensors, coolant and MAF sensors in the morningAny suggestions would be appreciated.Thanks in advance, Kevin

[NISTECH]

get a fuel induction service to clean the intake out and throttle body. but your fuel milage really doesnt seem all that bad for that kind of milage. you may be able to improve it slightly but I wouldnt hold to much hope in achieving 19 mpg freeway.

[kpuri]

1997 Pathfinder SEManufactured 8/96Auto Tranny102k

I ran a few more checks today O2/MAF checked out ok.I also ran another scan today and found a stored P0440 code Vent Control Valve (possibly circuit?)The part looks fairly easy to replace.

I remember hearing about a Nissan TSB on a P0446 possible being caused by a EVAP system pressure sensor.The remedy was as follows "Test the operation of the EVAP system pressure sensor. If necessary replace the sensor with the countermeasure part in this bulletin."

Any suggestions on test procedures for the pressure sensor and control valve would be appreciated.

Thanks, Kevin

[NISTECH]

pull the hose of under the hood that goes to the evap purge control solonoid. If black gravel(charcoal) comes out of this hose you are gonna need more then the vent valve. if there is no charcoal there then replacing the vent valve is al you will really need it is probably stuck open. I have done several of those valves due to rust on the pintle inside. the charcoal in the lines situation only a few times which required replacement of the canister, vent valve ,purge valve, pressure sensor, and clean out the lines with compressed air. Oddly the canister cars where all from colorado!!

[NISTECH]

BTW p0440 is evap small leak code. so most likely your vent valve is stuck open or your gas cap is loose.