MPG keeps getting worse. just burned 1/2 tank after 100 miles

[wu_tang]

a/c always on? bad or leaking injectors? O2 sensors?

Minimal AC use. And if there is a bad injector i havent seen or felt anything

 

[truWarier02]

And I thought mine wasn't that great.

I have an auto I4 with AC on most of the time during the day. I do 70%fwy (avg. 65-70mph) 30%city (avg. 35mph) and usually get approx. 350mi with 13gals, which rounds off to 26-27mpg.

But when I saw our EPA ratings of 20city 28fwy, I suppose my mpg isn't as bad as I thought. I'm still stumped by how some members on here could average low to mid 30's though.

 

[twofast4u]

if your cat converter was plugged like no tomorrow, that would cause bad mileage with no CEL....

 

[Chris Vu]

I get ~100 miles for the first half, but then when I get close to empty, I'm at around ~350 miles .. if I drive purely highway, I get about 380-390 miles by the time I get close to E. I don't know why, but I find it pretty retarded. I'm use to it now though. As long as I hit 350 miles by E I'm happy.

 

[bagoon316]

I get ~100 miles for the first half, but then when I get close to empty, I'm at around ~350 miles .. if I drive purely highway, I get about 380-390 miles by the time I get close to E. I don't know why, but I find it pretty retarded. I'm use to it now though. As long as I hit 350 miles by E I'm happy.

Mine is opposite, on a good tank, and good driving, i'll easily hit 200 miles on the first half. Second half, I get about 125-150. I drive mixed use, probably 50/50 highway/city. My avg MPG is only about 24, sometimes less if I've had a "rough week" running late everywhere. Or feeling frisky

 

[001Stunna]

Replace Spark Plugs (gapped correctly)
Replace Distributor Cap & Rotor
Replace or Clean Air filter
Check and replace spark plug wires if they show signs of arcing or tears
Seafoam in tank and through pcv hose
Set tire Pressure at 34-36psi when cold
Check the o2 sensor voltage using an OBD2 Code Reader with live readings and replace if necessary.
Checked for bad wheel bearings or possible dragging rear drum brakes
Take extra sh1t out of the trunk
Try and not do a lot of short stops if you can. Mix your errands together.
Accelerate like a grandma making the car shift gears at no higher then 2.5k rpm in all gears.

 

[wu_tang]

my passenger rear tire was at 18 psi

 

[wu_tang]

Replace Spark Plugs (gapped correctly)
Replace Distributor Cap & Rotor
Replace or Clean Air filter
Check and replace spark plug wires if they show signs of arcing or tears
Seafoam in tank and through pcv hose
Set tire Pressure at 34-36psi when cold
Check the o2 sensor voltage using an OBD2 Code Reader with live readings and replace if necessary.
Checked for bad wheel bearings or possible dragging rear drum brakes
Take extra sh1t out of the trunk
Try and not do a lot of short stops if you can. Mix your errands together.
Accelerate like a grandma making the car shift gears at no higher then 2.5k rpm in all gears.

 

[truWarier02]

my passenger rear tire was at 18 psi

 

[Simkid5614]

Also, Correct about the platinum/copper debate, On my previous car,

If you ran coppers you would get 30-35MPG 02' Saturn 5MT
Platinums would foul up by about 3-5k miles, would need replacement and would make mileage drop to 18mpg.