[kms1990]

i get anywhere between 250 and 300 miles out of a full tank, change your pcv valve its cheap and easy to do and can help alot with mpg and if you have any noticeable power loss it can help that. the investigate your evap leak. try a gas cap lokk at the seal around the cap if it has alot of or any big cracks in it or chunks of seal missing get a new one and it should fix it that seal keeps pressure in tank and can throw a p0441 or other evap leak codes if it goes bad.

 

[kms1990]

maf is mass air flow sensor its the square sensor located in the air intake tube behind the air filter box, be careful cleaning it, use only mass airflow sensor cleaner and dont touch the little things dangling in, only the plastic. could be the winter fuel mix, in texas it doesnt seem to affect vehicles as much but if your elsewhere it might. check out your vacuum leak it maybe causing it, check your fuel filter, that is a cheap way to start to see if it helps. may also run a good fuel treatment such as lucas deep clean or rxp (ask at counter at autozone) (both work good) run that with a new fuel filter. do the pcv valve at same time total parts are about $18 and will maybe take 20 minutes o do total (your pcv valve is located near the n on where it says nissan on the engine in the front most vacuum line running from there. also make sure your not leaking fuel anywhere. let us know if anything helps and keep us up to date and feel free to post up or private message me if you need help.

 

[kms1990]

what is the PCV valve? I started following this thread because i've gotten bad MPG since i bought my 04 X in summer of 2011. did knock sensor relocate, put a short ram intake on (helped slightly) but i can't seem to track down why i'm only getting 13.5-15 mpg. i've done the math on like 50 tanks and always fill at same pump. can't figure out what is wrong.

a pcv valve is the positive crankcase ventilation basically your engine builds up toxic fumes in the combustion chamber and if they cannot be released the pressure builds and can cause all kinds of issues it can foul spark plugs cause your oil to go bad prematurely and even blow seals in the engine if left unchecked. this pressure build up can cause loss of power and loss of gas mileage, those are usually the first 2 signs of a bad pcv valve. also check your fuel filter these 3.3l engines change are very sensitive to that fuel filter being replaced and if you dont they will drop in as mileage and power and if left long enough could foul out injectors both parts run you about $18 to buy $11 for the fuel filter and $4 for the pcv valve and both are easy to change (20 mins max ea.) and the pcv most of that will be fighting to get the hose off (they get tight). also if your check engine light (cel, or mil) is on get the codes read that might point you to the issue

 

[kms1990]

I hope it's not a fuel leak. My neighbor has the same year Xterra, but his is an SC. He said his gas tank was leaking. Supposedly they're plastic?
I hope to get to do my oil change, PCV this Tues. I work Thurs-Sun. Weather pending as well. If its raining or snowing, that puts a damper on outside projects. Lol

my 2000 has a metal tank with a metal skid plate under it (se came with it) you may have a leaking injector.

 

[kms1990]

It's a vacuum/spring regulator and a return fuel system. The fuel pump could pump a million gallons a minute, won't make a difference.

And you do know that it's perfectly normal for the engine to build up toxic fumes in the combustion chamber, right? That's what a combustion chamber does, deflagrate the air/fuel mixture (that's the internal combustion part of the internal combustion engine).

PCV valves provide negative pressure on the backside of the pistons and expel ring bypass gasses to help keep the oil cleaner and the engine a little more efficient.

I've had the same fuel filter for over 60k miles and have never changed my PCV valve. I have close to 120k miles on my engine and change my oil around 4k miles or whenever I get around to it. I get between 19.6 and 20.4mpg's.

A bad PCV valve won't trash your mileage, won't foul your plugs or destroy the ozone layer. Just helps with a bit of efficiency for the rotating assembly and get's the bypass out of the oil.

Gas tanks with the skid plates have been found to be rusting out due to mud and junk getting between the tank and the skid plate, causing the tank to rust on the bottom. I'd crawl underneath it and smell for fuel. If you smell fuel, get to a shop and find out why.

well maybe your pcv valve is fine, a bad one can cause blow by which is what fouls the plugs not the actual valve and yes it is normal for your engine to build up toxic fumes the pcv system rids them and sends them to be reburned so as not to gum up the oil and cause sludge and oil leaks, that pressure however can cause a small, but sometimes noticeable mpg drop and if your plugs foul or are old it can cause more mpg drop

 

[kms1990]

It's a gimmick, don't bother.

X2! probably needs a tune up too how many miles are on it?

 

[kms1990]

i think my air filter is fine. i put a weapon r short ram on not too long ago. i've been chasing this problem for awhile and now that i have resolved my KS issue and did the relocate mod for that, this is my best option to try next. hopefully this will resolve the issue. should i do the seafoam too?

that seafoam helped mine out alot aand yeah your right at about the mileage for its first major tune up you need to think about spark plugs spark wires cap and rotor (distributor) also your timing belt service this is an absolute must, its expensive but WILL save your engine down the road and DO THE WATER PUMP at the same time, and do the aternator, power steering ect belts. and all the tune ups

 

[kms1990]

yeah but could possibly be the oil pump going bad check that sending unit first as it would be a cheaper fix. check for leaks near that unit as it maybe causing low pressure

 

[kms1990]

maybe you got some water on or in the electrical parts of the oil pump.

 

[kms1990]

odd, i wash my truck once a week (at least) i like to keep it clean! and have never had any wiring issues then again mine is a 2000 not a 2004 so the way they did the wires is most likely different or maybe on the 04s the wiring can slip loose from a holder somewhere it wont get wet and get to where it can, might check that out, or wrap it in some electrical tape

 

[kms1990]

did the sputtering start when you did the seafoam in vacuum line? if so did it stop after you stopped pouring it in or no? if no check the vacuum line you used to pour it in and make sure its tight(if tight check your spark plugs, wires and cap and rotor on distributor or it may have the first signs of a failing distributor, my dizzy gave me a bad idle for about 3months before (not hardly noticeable but the occasional, rhythmic off feel in the idle then the other day the dizzy quit on me so just a thought, dont freak out and go buy a distributor until you have narrowed it down). if it was just when your pouring it in thats normal as you are basically creating a massive vacuum leak to do it. the smoke in the engine bay is not your valve covers its the exhaust manifold that has cracked (most of us have that, both sides on mine are) if its not throwing a check engine light for o2 sensors or cats then dont worry about that as it wont hurt anything (or hasnt on mine, and mine still passes inspection and runs just fine with it that way)

 

[kms1990]

i would suspect a vacuum leak then check all the hoses you touched for tightness and replace that hose clamp should fix er right up