So im getting like 12mpg in my 05 g35. Ive changed the sparks, the 02 sensors, and cleaned the mass air flow sensore. Ive been getting this mgp and sometimes worse even before i got a cat back. Ever since i got the car. What do I do

 

Lighten the pressure you apply to the throttle.

 

Lmao i have been

 

X B, have there been any CELs? 12mpg is really low, and could indicate a problem(maybe serious). I'm 9 1/2 weeks into the ownership of my G, and it gets ~19-20 city, which is normal, and I rarely "get on it".

You should really get it checked out by a professional. Good luck.

 

How does it run? Hows the power? U do have your E-brake off, right?

 

Based on 10 years of G ownership and also here on the forum 19-20 isn't "normal' for all city driving 15-18 would be considered normal, remember it was rated from the factory 17 city, 25 highway. If the car's driven with any amount of hard driving it's not out of the question to be getting 12-14. There are exceptions to this of course but they're not "normal."

 

Ahhh...I had misread the statements/rating concerning fuel mileage. 20 was the "combined" I had read. My tune-up work, plugs/a-f/engine oil&filter/trans-diff gear oil changes must be working!

Cool, thanks for sharing the experience knowledge...greatly appreciated!

 

12 is extremely low. Are you running premium ATM?

 

Sorry for the late reply. Ive had a check engine like for a very long time. Even befor i put test pipes. Every time i go to get it checked out, it always says its the 02 sensors but ive changed them out a few times. Even the dealership went through extensive testing and only found the 02 sensors.

 

How exactly are you calculating mpg, are you using some kind of plug in tracker that might not be functioning correctly or are you using the trip odometer and dividing miles / gallons of fuel on the next fill up.

 

It runs good, power is there. And yes my ebrake is off lol

 

Yes i divde the miles i dribe by the gallons

 

Get the vehicle up on jackstands and spin the wheels by hand with it in neutral to verify something isn't dragging.

Check your tire pressure (tpms might be malfunctioning).

Have the vehicle aligned (toe causes major friction and severely reduced mileage).

Pull and inspect the plugs, they tell you almost everything you need to know about the conditions in the combustion chamber.

Clean/replace your air filter, clean the MAF, inspect and clean the TB if necessary.

Inspect/clean the PCV valve.

OBD2 realtime scan the O2 sensors to verify they're cycling properly at idle and with throttle.

Remove/inspect the CATS with an inspection mirror or borescope for any melting on the media.

Smoke test exhaust system for leaks.

Run seafoam through the gas tank.

Perform an ECM and idle recalibration.

 

Sorry if this seems obvious, but you FILL the tank up until it clicks off ?

 

My younger sister owned my G35X, new from the dealer, and the combined MPG was 19.something. I will bet that she never reset it in 10 years either. In the 12+ months I've owned it, I did reset it (multiple times) and it always falls back to 19.something with my driving too. I don't drive like a grandma but I also don't drive like a 17-year old. I do open it up often enough.