Only getting 12.3 mpg!!!! Whats going on?

[robert]

i currently own a 98 pontiac firebird 3.8 with no major mods, my o2 sensors are fine my oil filter is new my fuel filter is new, i have a lot of air flow (Ls1 intake) new IAT, i seafoamed the car, im out of options What else can it be?

[97rs4life]

Re: Only getting 12.3 mpg!!!! Whats going on?

plugged cat, spark plugs, wires, coils, injectors, and more can cause fuel mileage issues. Also a lead foot

[robert]

Re: Only getting 12.3 mpg!!!! Whats going on?

i have been taking the car easy keeping it under 2.5k and the spark plugs and wires are all still good, can the cat cause that much of a loss?

[cam98aro]

Re: Only getting 12.3 mpg!!!! Whats going on?

how are you calculating mpg?

are you using a tool, or doing the math yourself?

[robert]

Re: Only getting 12.3 mpg!!!! Whats going on?

do it my self i set the odometer to Zero when i completly fill up and when im empty i take the miles and divide it by 15 gallons which is what my car tank is.

[cam98aro]

Re: Only getting 12.3 mpg!!!! Whats going on?

well thats why, you are doing it wrong

you need to fill it up all of the way 100% full, write down the mileage, drive around, fill the tank up again, see how many gallons you put in to make it full again, then divide that number by how many miles you drove

there is usually 2-3.5 gallons left in the tank when it reads E

and your tank is 15.5 gallons

[nascar24jd]

Re: Only getting 12.3 mpg!!!! Whats going on?

X2...

Also, you don't need to run it empty. You can run it to half a tank and then fill it up and do the calculations.

[pathology knight]

Re: Only getting 12.3 mpg!!!! Whats going on?

yes, if you reset your trip od to "0" and then drive around like normal and then put gas in it again (when every that is....you don't have to be on empty).

fill up your tank.
take the miles you drove (per od) and divide by how many gallons you put in (per gas station tank).

example: 325.7 miles. filled up with 14.2 gallons.

325.7 miles/14.2 gallons=22.9 miles per gallon.

[venom3300]

Re: Only getting 12.3 mpg!!!! Whats going on?

^x2

and if u drive like me u still get 16mpg lol

[Cammy98]

Re: Only getting 12.3 mpg!!!! Whats going on?

Hah im pretty heavy on the gas I get about 15-16 mpg. 20+ on the highway.

[venom3300]

Re: Only getting 12.3 mpg!!!! Whats going on?

ya i get 15-16 to school and back, 22-24 highway, 27-29 interstate

[bwkmaro]

Re: Only getting 12.3 mpg!!!! Whats going on?

if ur getting 12mpg ur either doing ur math wrong or some thing uve put on is ****ing up. i beat the poop out of my car and never get less than 20 and 24 if im easy so u shouldent see under 15 ever.... and also if ur cat was plugged you would know it first off you'd have no power and theres a good chance you'd throw a misfire code