Yeah seriously that is just crazy not going about 2100 to save a little gas. Holy hell please do go by a hybrid if your worried that much about gas.

 

OP - Unless you are constantly ABOVE 4000 RPMS you should not be getting that kind of gas mileage. How many miles do you have? You should consider changing your PCV valve, Thermostat, and Upstream O2 sensors.

Fuel consumption is a combination of throttle (gas pedal) position, Load on the engine(gear/hills), and RPM. For every rotation the injectors will squirt fuel into the cylinder so obviously the more RPMs the more fuel. Throttle position and load levels change the map that the ECU uses for A/F ratios and thereby will increase or decrease the injector pulse width per RPM.

If you are shifting between 2500-3000 rpms in city driving you should be getting at least 15 mpg assuming you live in a very hilly area, otherwise you should be closer to 18-20 mpg. This will vary with spirited driving some, but 15 MPG should be a MINIMUM unless you are on a track.

I have 163K miles on my car now. I drive it pretty hard a lot of the time I'm driving. I average around 19-20 MPG around town in the summer and 17-19 in the winter.

You need to go figure out what is going on.

 

^^^^^Using to higher gear at a low speed say 6th at 30mph as mentioned previously in the thread. Puts a alot of load on the engine so it's throwing petrol in to stop it stalling. It's constantly in a state of being bogged down and not running freely with no stress.

Also coasting uses up alot of petrol. When a modern engine is in gear rolling along to a stop or red light with no accelerator input it uses no petrol what so ever-non is injected into the cylinders. As soon as a manual car is put in neutral and is rolling along the engine still needs to maintain an idle speed, so will inject fuel to keep it at "tick over speed". A complete numpty came up with that idea or someone who doesn't understand modern fuel injection systems.

Whats going on is someone needs to get back in an automatic and leave the manuals to the big boys lol.

I too get similar milage in mine round town to you. Obviously more gear changes and touching boost at times brings it way down, long steady runs with few gear changes sees it at 26mpg...

 

Thanks for the advice, everyone else is going nuts about their masculinity and how it relates to shifting at lower RPMs...

Yeah I honestly don't floor it or go nuts, I'm babying my car since I got it 3 weeks ago, and it has 75k miles on it. TBH though I have sped up a few times for fun, but maybe only for a few minutes out of 100 miles of driving, when I calculated my 9.3 mpg. I've been revving only up to 2.5k from the last fillup and yet I'm already at around 40% on the gas gauge and at 80 miles. I know that's not really 40%, but even if its 70% thats still about 11.5 mpg so something mechanical may be wrong. Ugh. I'll have to wait until I go home for spring break to get my mechanic to check it out. Is there anything I can do right now myself?

 

As for the chest beating and masculinity issues, I'll leave that to you US guys, some of us who can actually drive, and enjoy driving have simply been trying to educate you guys, but its obviously a lost cause

As far as your fuel consumption, it still sounds like you are not calculating correctly, or the is a problem with your car, and i suspect its either lambda or ECU WT or IAT related, get it looked at rather than keep trying to second guess the MPG.

 

If it is correct your mpg calculations, look into the O2 sensors. A faulty one may cause the car to run rich hence the crap mileage your getting.

Are the exhaust tail pipes getting coked up on the inside(black n sooty)-this proves that fuel is being burnt properly. If not i expect it to be runing rich. Maybe wipe the as best you can inside and run the car for a tank or 2 of fuel. If they stay relativley clean then fuel isn't being burned fully in the engine...

 

Thanks for the DIY tip, definitely try that soon.

 

It's free and it's worth a shot

Did this on mine when fitted a new exhaust. It didn't seem to be getting dirty on the inside of the tailpipe and it had been on a while....confusing.

Then when upping the boost a little (R33GTST) it had a real bad miss fire at 5000rpm. It was traced back to worn coilpacks not supplying the spark plugs with enough proper currrent so i was getting an in-efficient burn in the cylinders. The boost was effectivly blowing the spark out! New coilpacks and spark plugs fixed it a dream. I know it's a different car but still has an electrical ignition system and can tell when mpg's are down..

 

You are talking about oil consumption, right?
Seems about normal...

 

Enigmatic42..... I just re-read your first post about re-setting your trip computer and you say you filled the car up with 93 (mon?) rated fuel. Now isn't that the lowest grade fuel you can get over there? Thats your problem right there...

I'm pretty sure these cars have a self learning ecu that can advance or retard timing for performance/economy gains. I know my 1994 nissan did.... By putting in the lower grade fuel the ecu has to put in more fuel to get the same bang you would get if you were to run it on premium or super unleaded fuel. The timing will also probibly be retarded slightly.

Using a better fuel coupled with better driving techniques will give you better mpg's simple. A higher MON or RON rated fuel is more volitile so when in the combustion chambers gives a better burn/bang per buck so to speak.

Don't be tight put proper fuel in it . Or get rid of your 3.5litre V6 and get a 2.0 v-tec honda...

Remember over in Japan they have 100RON rated fuel, thats a little better than what we get over here with Shell V-Power in the UK(98 or 99RON). Manufacturers have to take into account fuel quality world wide so the car is tuned to run/work all over the world with a compromise on performance. I have totally removed this feature from mine like many other owners over here into there performance cars. If i ran my car on 95RON fuel now(lowest we have here) yeh it would work but not for long it would start to DET and then blow up. Simply because the fuel isn't good enough and stable enough.

Ask the Nascar guys what they use. Tell you now racing fuel is anything from 105RON to 110,120+RON not the 93 bath water you get on the street

 

93 octane is the highest grade in the states, so i'm sure its equivalent to your 98 RON over in europe. They made the infiniti g35 to take 93 octane in the US, not anything else. I appreciate the joke about I should be driving a honda cause I'm not informed about gas octanes in my own country however. >.<

 

Your forgetting that the G35 is designed and manufactured in Japan with the US gas and emissions in mind, and built in the US, so it will have no problems with there fuel, but in any case there 93MON is equivalent to our 98RON.

Also the ECU while being a clever little sod, has limits,you can run 95RON in the 350GT and it will cope fine, and will still return pretty much the same MPG, you just wont have quite the same performance
and if you consider that the 350GT ECU is actually designed for 97-98RON as although 100RON is readily available, since 1999 the Japanese manufactures have been optimizing the fueling to run the lower RON fuels.

 

US fuel is rated as (RON+MON) / 2. 93 R+M/2 = is near 100RON.

Higher octane means fuel is less prone to detonation, so you can use a higher compression ratio. Higher compression ratios are what's responsible for better power and better gas mileage because they're more efficient. You can put million octane gas in our cars, and it's not going to help with power or efficiency.

Nascar engines run at 12:1 compression, while the VQ35* engines are 9.8:1, that's why the difference in octane requirements. It's irrelevant whether the engine is a 2.0L-VTEC or a 5L-V12, what matters is compression. My other car has a 1.8L supercharged four-cylinder engine running 11.5:1 compression, and it's much more picky about fuel then the engine in my G35.

As long as the fuel you put into your tank has sufficient octane not to detonate at the most advanced timing possible, the car will run at the same efficiency. Using too low of an octane means the engine has to retard timing to prevent knock, which is less efficient, hence, worse mileage.

 

Unless you're pegging like 8K in 1st everywhere you go and never change gears, I'd say it's way low.

Something be amiss somewhere if you're really pulling only 8.

 

So OP did you ever look into cleaning out the TB and the rest of the maintenance? Filter, oil, etc.