94 5.0 lost half mpg

94mustanggtfast · Jul 7, 2011

i have a 94 mustang gt with 135000 miles and the 5.0 and its automatic (aode) a year ago i was getting 300 miles to a tankof gas. now i barley make it past 100 miles. it had 2 codes in it saying it was running rich. i changed my airfilter and cleaned my MAF i was told it could be my fuel pressure regulator or my 02 sensors how do i test these or do i just swap them?

lutter94 · Jul 7, 2011

Your information is not very accurate....haven't you ever calculated fuel mileage???? Was one code left bank rich and the other right bank rich? Seems strange that both o2's would take a dump at the same time. Did you put 100LL in it???

94mustanggtfast · Jul 8, 2011

it went from 23mpg to 11 mpg. yes i had 4 codes 2 for left bank rich and 2 for right bank rich. what is 100LL?

CC'S95GT · Jul 8, 2011

100LL is aviation gas but racers like to use it too. It has lead in it and the lead will foul you O2's.
Your O2's are probably origional and are due for replacement.

lutter94 · Jul 8, 2011

CC'S95GT said:
100LL is aviation gas but racers like to use it too. It has lead in it and the lead will foul you O2's.
Your O2's are probably origional and are due for replacement.

Yep, what he said....it stands for 100 Octane Low Lead. Always used to put it in lawn mowers, the go kart, and atv's back home.....really hard on cats, and can screw up o2 sensors as well.

Throw a couple new o2 sensors on it and see what happens.....she should run like new.

ttocs · Jul 8, 2011

why did you put high octane expensive gas in your lawn mower?

duh09 · Jul 8, 2011

ttocs said:
why did you put high octane expensive gas in your lawn mower?

That grass is tough, gotta be able to chop at super speeds

CC'S95GT · Jul 8, 2011

hovercraft/ lawnmower.

94mustanggtfast · Jul 8, 2011

no just 93 octane for me lol have not tried race fuel yet

akaslick15 · Jul 9, 2011

not to steal your subject bro sorry but man im on the same page ive heard people are getting like 250 to 300 miles on full tank but when it comes to me if im lucky i will only get 110 miles for full tank which is really pissing me the f*ck off sorry guys but i have already did spark plugs wires cleaned the maf cleaned the iac cleaned the TB changed fuel filter like what the hell if anything the car runs beautiful but prolly got worse on gas after all that lol can o2 sensors really kill gas millage
like that from running rich?cuz im forsure running rich but have no light on

ttocs · Jul 9, 2011

the people that get 250-300 miles a tank drive carefully to save gas. I can get 250 per tank if I drive it like I want it but normally with the mods I have 12-17 mpg is average.

what mods are done to the car?

akaslick15 · Jul 9, 2011

nothing but a 2 and a half exhaust with no cats soon in like a week im throwing 4.10s on it and thats about it
sounds messed up right?

ttocs · Jul 9, 2011

well if you are worried about milage I would not suggest gears...

akaslick15 · Jul 9, 2011

well i should be getting more than 110 miles per tank thats all im saying

94mustanggtfast · Jul 9, 2011

no mods except for off-road x-pipe and flowmasters. i would drive it hard and still get 250-300 to tank now i take it easy and get 100-150 mpg so ima try 02 sensors next

toyman · Jul 9, 2011

If the O2 sensors have seen 60k+ miles they will be lazy and should be replaced. For a car that runs in closed loop the PCM needs an accurate O2 sensor reading for optimum fuel economy.