20 mpg- why?

[ScoobKing]

I have recently done a tune up on my 93 1.8l. I did air filter(K&N), fuel filter, plugs and wires. The car was getting about 15 mpg before I did that. Now it's about 20mpg. I know it should average about 25-30. I'm not getting and check engine lights or rough idling. It feels like it's running great but the mpg is still a bit low. Did I miss something?

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[silver2004impreza]

The O2 sensor maybe? It might be getting sluggish, causing the computer to throw too much fuel at the wrong time. I'd recommend getting one from the dealership, or from a vendor here on NASIOC. I'd steer clear of the "universal" ones though. All the universal ones I've used have been junk.

[Doc Holiday]

How heavy is your foot, how much traffic do you sit in, etc

[ScoobKing]

I drive it pretty lightly and traffic is almost never a factor. I was thinking it might be the O2 sensor but it doesn't throw any codes for it. Would it do that if it was bad? I work at a NAPA a block away from the dealer. I wonder if I should use a Bosch OEM style sensor or if I should try the dealer since I can get one for a little bit more money.

[ScoobKing]

Bump!

[JamesWilson]

Tire pressure and tire condition, condition of other drag items like wheel bearings, brakes. Condition of engine (good compression, oil pressure) and overall health. Belt tensioners/rollers dragging, ps pump dragging, alternator dragging. O2 sensor is fairly huge, as well as a certain driving style that will have it run in closed loop mode = better fuel mileage. A/C versus windows down has an effect also on aero drag.

I tested with a lot of this, I used to drive 400+ miles per day for a job years ago, same freeway route (<5% street/city), makes a big difference. I overinflate my tires by up to 4psi, run good quality synthetic oil (German Castrol/GC 0w-30 was 2mpg lower than AMSOIL 5w-30 or Pennzoil Platinum 5w-30 in my testing) , make sure I drive the car lightly especially before it reaches operating temperature, no jackrabbit starts, feather the throttle at all times, coast down long (.5 to 1 mile) hills in neutral (may be illegal in some states), never above 70mph, windows rolled UP even in the summertime. That's the difference between 38mpg and 45mpg in a '94 Suzuki Swift GT (1.3L DOHC screamer)

[Ioku]

I am also getting bad mpgs with my 1.8, I'm changing the plugs, fuel filter and air filter today, so that should help, but i was also thinking the O2 sensor could have some thing to do with it. But where is it on the car and what dose it look like any1 have a pic. thanks.

[Doc Holiday]

Originally Posted by JamesWilson

Tire pressure and tire condition, condition of other drag items like wheel bearings, brakes. Condition of engine (good compression, oil pressure) and overall health. Belt tensioners/rollers dragging, ps pump dragging, alternator dragging. O2 sensor is fairly huge, as well as a certain driving style that will have it run in closed loop mode = better fuel mileage. A/C versus windows down has an effect also on aero drag.

I tested with a lot of this, I used to drive 400+ miles per day for a job years ago, same freeway route (<5% street/city), makes a big difference. I overinflate my tires by up to 4psi, run good quality synthetic oil (German Castrol/GC 0w-30 was 2mpg lower than AMSOIL 5w-30 or Pennzoil Platinum 5w-30 in my testing) , make sure I drive the car lightly especially before it reaches operating temperature, no jackrabbit starts, feather the throttle at all times, coast down long (.5 to 1 mile) hills in neutral (may be illegal in some states), never above 70mph, windows rolled UP even in the summertime. That's the difference between 38mpg and 45mpg in a '94 Suzuki Swift GT (1.3L DOHC screamer)

amazing how cars can get mileage that is just as good as a hybrid with a little common sense/know how

[ScoobKing]

Originally Posted by Ioku

I am also getting bad mpgs with my 1.8, I'm changing the plugs, fuel filter and air filter today, so that should help, but i was also thinking the O2 sensor could have some thing to do with it. But where is it on the car and what dose it look like any1 have a pic. thanks.

The 1.8 has only one O2 sensor. It is located on the passenger side of the motor back near the diff. stick. The wire is kinda near the axle. It's pretty easy to locate since there isn't many wires back there.

[ScoobKing]

Originally Posted by JamesWilson

Tire pressure and tire condition, condition of other drag items like wheel bearings, brakes. Condition of engine (good compression, oil pressure) and overall health. Belt tensioners/rollers dragging, ps pump dragging, alternator dragging. O2 sensor is fairly huge, as well as a certain driving style that will have it run in closed loop mode = better fuel mileage. A/C versus windows down has an effect also on aero drag.

I tested with a lot of this, I used to drive 400+ miles per day for a job years ago, same freeway route (<5% street/city), makes a big difference. I overinflate my tires by up to 4psi, run good quality synthetic oil (German Castrol/GC 0w-30 was 2mpg lower than AMSOIL 5w-30 or Pennzoil Platinum 5w-30 in my testing) , make sure I drive the car lightly especially before it reaches operating temperature, no jackrabbit starts, feather the throttle at all times, coast down long (.5 to 1 mile) hills in neutral (may be illegal in some states), never above 70mph, windows rolled UP even in the summertime. That's the difference between 38mpg and 45mpg in a '94 Suzuki Swift GT (1.3L DOHC screamer)

Very true what you say about tires, A/C, brakes, etc. The tires are new and I check them at work at least once a week. Since it is the winter time I don't see too much need for A/C or open windows. Even with the A/C on it doesn't harm the gas mileage by even one mpg. That has already been proven. My cam seals are leaking a little bit and I am just about due for a timing belt job also. How much do you think that would harm the mpg? I'm sure my oil pressure is a bit off. I'll probably get the tensioners changed while the belt is off. Bottom line...Thanks bro...


And now.....work...

[ScoobKing]

My timing belt is done and I took a drive to South Jersey. It seems to have slightly better mileage but it still isn't where it should be. I am going to just go for the O2 Sensor and see what happens with that.

[nstag8r]

I don't know about ya'll but my MPG goes down everytime my right foot gets heavier, SHRUG

[Chino Bling]

i consider myself driving conservatively if i get 20 mpg..

[nardvark]

Part of me wants to be non-constructive and say "your car is 15 years old, why are you worrying so much?"

Are your drivetrain fluids relatively fresh? Your guess about an O2 sensor is probably pretty good. They can start to go bad long before throwing a code and degrade your fuel economy.