I have a 2008 infinity g37 journey base model that is running 13.8 miles a gallon what could it be idk how long the sparkplugs haven’t been changed out has this happened to anyone ?

 

Check air filter, sparks, clean MAF sensor and cleak throttle bodies. That is really weird 13.8 mpg, The least I had was 16.9 mpg but I was doing really high speed for a very long time. Also next time you fuel up record how many gallons of gas you put in and set your trip A or B and when you are at empty divide it and it will give you a much accurate reading of you mpg. Maybe your mpg calculator in the vehicle is not functioning right. Or you might have just recently reset it and drove aggressively.

 

First learn how to spell Infiniti
This site is for a car not speakers
Before you do anything fill your tank. I always use regular 87 octane. Reset your odometer to zero. Reset the vehicle computer
Drive on an interstate for 250 to 300 miles or until you reach 1/4 tank at the speed limit or slightly above no cruise control
Refill the tank
Divide the gallons it took to refill the tank into the miles traveled on your odometer
If you see 24 MPG or above there is nothing wrong with your vehicle
Plugs are good for 105k miles

Telcoman

 

Don't we have an 11:1 compression ratio? That means 93 octane..... Knock sensors will retard the timing and save your engine, but 87 certainly isnt healthy. I've never had a car that takes regular fuel though.

EDIT: the filler door says premium fuel only. Use 93 or higher!

 

If you have any questions about your Nissan/Infiniti, never mind the owner's manual; dial "0" for telcoman!

 

I use 91 and my car still sounds like it knocking like crazy. lol

 

Do not use 87 that’s dumb use 91 or 93 what is recommended

 

Don't use 87. I always (try) use Shell 93.

 

This is is to share a point of fact.

I have a 2013 6MT. According to my car’s manual, our premium fuel (91 Octane minimum is REQUIRED.

The manual also also says that it can use regular with reduced performance. I suspect that the car is smart enough to detect the octane and adjust the timing.

To avoid issues, I only use Top Tier premium.

Regarding fuel economy, our G-37 is not the most efficient.

I replace the air filter and put Chevron Techon concentrate every 9-12 month.
My overall MPG averages 21 MPG (23.5 highway and 13 city).

I normally drive gently except when I let it fly from time to time (what good is it if we don’t enjoy it)

hope that hat this helps

 

The two biggest causes of poor fuel economy are the driver's right foot and bad O2 sensors. If the ECU isn't throwing a code, it's not the O2 sensors causing your issue.

 

It would seem it is pretty easy to get a wide range of MPG out of the G. Like slarti said right foot usually causes the biggest decrease (at least in my experience). If you keep the car routinely maintained (i.e. fluid changes, filter changes, clean throttle bodies etc..) and you drive reasonably there's no reason it shouldn't average 21-24. Also FWIW when my G was my daily driver, I always noticed approx. 2-3mpg drop when I switched to my winter tires, I also posited that winter blend gas may have some influence too. Warm weather months it was easy to get 25-26. I took the G on a family road trip to the beach a couple years ago and got 500 miles out of the tank with room to spare. Now that its just a fair weather car and I've recently installed some new parts I tend to stay in sport mode more and spend less time on the highway, I've been getting more like 19-20.

If you really want better MPG make the G a weekender and get a Q50S Hybrid 360hp, plenty of instant torque and as a daily driver I avg 31+