Hey you guys, long time no talk. After having gone to 2 general mechanics in the last 6 months(owned the car for 8 months) and nothing showing up on their diagnostics, i went to infiniti dealer today. just got my 2004 g35 coupe (auto) back and i was hoping they could tell me what was wrong but it turns out the "car is running perfectly." i am really running out of hope and think im going to have to get rid of my baby G. to much money being wasted on gas when it shouldnt be. my gas consumption when from about 180mi every 17-18 gals to now about 135. any advise would be appreciated as i rly want to keep it.


things ive done:

New k&N air filer
New Platinum tipped spark plugs
BG air intake system cleanse
regular oil changes...first i used castrol syntec then changed to royal purple
93 gas everytime
gradual accelerations at about 2000-2500rpm

fyi:about 7 months ago my service engine light turned on so i went to advance auto to get codes read. it threw a running rich and evap system small leak codes dude deleted it and never came back on.


my friends, i really need your recommendations. what else can i look for? thanks in advance.

 

Fuel management system

 

thanks for the reply. im not to auto savvy, can u please elaborate. should a computer diagnostic have picked up a bad fuel management system? how do i know if its bad? thanks again

 

I suggest try reseting the ECU to let the computer learn your driving habbit.
https://g35driver.com/forums/engine-...resetting.html

Also clean out the Mass Airflow Sensor in the engine bay. You will need a TORX 20 bit to open access the MAS sensor located in the intake (near the dip stick). You can get the CRC MAS cleaner from Autozone.

Don't forget to clean your air filter if you haven't done so.

 

Maybe take it to a dyno tuner and have them monitor the A/F ratio to see if it's running rich. You might be able to get a custom tune that leans things out a bit.

 

Sounds like maybe your fuel sending units?

 

Is your car one of the recall unit that has problem with fuel line crack and leak evaporation emission control system ?

HTSA Campaign Number: 05V555000
http://www.lemonauto.com/complaints/infiniti/g35.htm

 

thanks for the reply guys. i actually did reset the ecu this morning but have not cleaned out the MAF sensor. will give that a shot. air filter is clean and was recently changed

infiniti said my car did not have that recall.


should any general mechanic have a dyno tuner?

 

No, you will need to go to a performance tuning shop that has a chassis dyno and has experience working with Nissans/Infinitis.

And the fuel tank sending unit doesn't affect mileage - just the reading on the gas gauge.

 

thx G35from PA...i am definitely going to give that a try. so strange 2 mechanics and even infiniti dont know whats going on.

 

I'm intrigued. So you were getting roughly 10 m.p.g. and now it's dropped to 8 m.p.g. ?

It's difficult to believe the car would be drivable if the engine were truly ingesting that much fuel...you're talking about less than half the gas mileage I get. That means your engine has to be processing more than twice as much fuel as mine does, and I can't make this work in my head. If my car runs a 14:1 air/fuel ratio, yours would be running a 6:1 a.f.r. - and I don't think the engine is capable of running that rich.

It seems like there must be a problem elsewhere, or multiple smaller issues that are adding up.

Are your tires the stock diameter? If not, are you correcting your mileage calculations for the difference?

How are you calculating your gas mileage?

How are you getting 17-18 gallons of gas in your tank? I ask because even if I wait until the "low fuel" idiot light comes on, I still can't squeeze more than about 15 gallons into my tank.

You haven't forgotten to remove the parachute from the back of your car after you deployed it the last time you were drag racing down at the local strip? J/K

Since I can't resolve the engine running with a 6:1 a.f.r. ratio without at a minimum some serious drivability issues by using simple rational thought, I'd be inclined to start looking for fuel leaks, re examining the math and method I was applying to my m.p.g. calculations, and ensuring the car was parked in secure locations where I could be relatively certain no one was stealing gas from it.

Good luck resolving the issue. Please keep us posted on your progress.

 

the funny thing is none of the diagnostics hav picked up anything and they show everything is operating normally. i do have stock tires and are properly inflated. i have very good driving habits and i accelerate gradually otherwise i wouldnt even be complaining. when i get to gas stationi divide miles ive done since last fillup(i reset trip A) and divide by gallons filled. i do know that this car was originally in ny before i got it by one owner. ive had the car since oct 09 and didnt really notice the problem at first but once i did dealer said sold as is and nothin they could do =/

i rly dont want to get rid of it but might just have to

 

I noticed a DECREASE in MPG when I put a K&N in my wife's 05 G35 Sedan.
I called K&N to hear what they had to say about it, and was told that they do not claim to increase MPG, but only HP and performance.

I noticed slight increases in my 1999 Exploder 4x4, but I also modified the air box too.
Now, I use NAPA (WIX) air filters due to claims that oil soaked cotton types do not filter nearly as good.

I did notice a increase in MPG when I added a SBD Grounding kit to my 04 G35 coupe AT.

 

put the stock filter back in. and a dealer will be able to monitor your a/f and rear o2 readings. that will tell you if you are rich or not when they hook up c2. if the car was running anything more or less than stock a/f readings it would throw a code. if the a/f sensor went bad and you were running lean, it would throw a multi-cylinder misfire code due to a lean condition on that particular bank. and as far as an evap leak....it couldve just been that your gas cap wasnt fully secured. otherwise its a hose or valve issue in the evap system. BUT.....you COULD have a sending unit issue showing your gauge running innacurately as well.