nismospec

iTrader: (3)

looking for help/potential causes of a gas mileage drop.
car just passed 100,000. mods are in my signature.

i thought initially the drop could be bad plugs, so I had those changed out to iridiums and still not seeing any gains.

is it possible that the O2 sensors could be going bad and messing up the air/fuel ratio? i'm not throwing any codes yet, but could that be it? Is there any way to tell a bad O2 senor?

next thing to try was to clean the MAF, thought maybe that would help.
or finally, is it just time to get a tune to even out the mixture?

to put things in perspective, I put $25 in gas which got me to slightly under 1/2 a tank. 50 miles later, i'm nearing the 1/4 tank full. my computer is registering 20 avg mpg, but it doesn't seem right.

or could the gas gauge be giving out?
sorry for the multiple questions, but gas isn't cheap and lately it seems that i've been at the pump more often than usual.

sry110

iTrader: (17)

I would suggest tracking the mileage manually for a few tanks and do your best to keep your driving style consistent between tanks, and use the same brand and grade of fuel each fill-up. You will have to top off the tank and start tracking your data from there. No need to run the tank all the way down....topped off will be your datum point for tracking the mileage. (Even more ideal is to use the same gas station and same pump for each fill-up if possible).

How many miles per tank were you getting previously? What's your reference point?

Could be a bad fuel level sensor and/or gauge but you should be able to prove that to yourself when you top off your next fill. Take note of where the gauge is before filling and translate that into gallons (approximate of course) and then see how much is required to fill it up.

I doubt a tune is necessary. It wouldn't hurt but that seems like a solution to a different problem. In other words, if this is a problem with sensors or fuel gauges let's fix that first.

Cleaning the MAF sensor never hurts. I do that every time I clean out my air filter (bout once per year).

Have you recently installed wider (heavier) wheels and/or tires? Any other recent modifications that may have coincided with your 100k mile turnover?

nismospec

iTrader: (3)

will check into the full tank procedure.
used to get 400 miles to the tank if not heavy on the pedal. now i'm looking at low 300's.

no new mods, all have been on the car for sometime. same stock rims/tires.

i've never cleaned the MAF. clean my popcharger every other oil change, but never the MAF.
i've reset my ECU several times to see if that would help using the step by step procedure, but not sure if that ever helps.

bmccann101

iTrader: (16)

youre in texas, they use crappy gas in the summer..jsut saying, mine drops every year in the summer.

drivessidewayz

iTrader: (4)

^^ Fuel isn't the same year-round; they do change it. And I can't stress enough never, ever, EVER base fuel economy solely off of your fuel gauge. sry110 noted the correct procedure.

nismospec

iTrader: (3)

on that note, and without starting a new thread....any preference on gas?
shell, chevron, exxon, etc?

ehaalandtluk

iTrader: (1)

Shell for me. Also check that the pump certification from Texas department of agriculture is at least from 2009 or you're getting screwed.