95 impreza 15 MPG So bad need help

doctordbonedoctordbone Member Posts: 3
edited June 2014 in Subaru
So i just did a complete tune up on my 95 subaru impreza, changed sparks and plugs, changed oil/oil fiter, changed fuel filter, air filter, fixed exhaust leaks, and im still just watching my fuel gauge go down so quickly! i need some help if anyone can suggest something else please? i believe im getting like 13 to 16 MPG and i'm not leaking anywhere.. HELP


  • xwesxxwesx Fairbanks, AlaskaMember Posts: 15,852
    How many miles on the car and have the oxygen sensors ever been replaced?
    2018 Subaru Crosstrek, 2014 Audi Q7 TDI, 2013 Subaru Forester, 1969 Chevrolet C20, 1969 Ford Econoline 100, 1976 Ford F250
  • ateixeiraateixeira Member Posts: 72,587
    Can you clarify something? Has the mileage been bad all along, or just after you did this recent tune-up?
  • doctordbonedoctordbone Member Posts: 3
    i bought the car a month ago, and did that tune up and still have terrible mpg, i believe its a little better than when i first had it. there's 170k on the clock. Ive heard these engines will be good for a while. and what 02 sensor? in the exhaust? i dont believe i have changed it. Where else are the 02 sensors? and can they really cause that much fuel to be consumed?
    thank you guys!
  • ateixeiraateixeira Member Posts: 72,587
    You said "changed sparks and plugs", you mean wires and plugs, is that right?

    Next thing would be the ignition coil itself, which sends out the spark.

    Spark or fuel, and you said you already did the fuel filter. If power is OK it's not the fuel pump (it would hesitate or stall).

    You may want to do a compression test on all the cylinder to see if one of them is not sealing properly, if so 25% of the energy from the fuel is wasted, and it's basically running on 3 cylinders.

    When they do that, look for no more than 10% variance in the pressure in all 4 cylinders. If one of them is more than 10% lower than the others, there's your culprit.
  • xwesxxwesx Fairbanks, AlaskaMember Posts: 15,852
    Possibly, but they tend to be additive problems that cause that poor of mileage. If you want peak fuel efficiency, you need well-functioning airflow sensors, vacuum system, EGR system, and oxygen sensors. There are two oxygen sensors, both in the exhaust system - one is upstream of the catalytic converters and the other is downstream.

    I would start with the vacuum system - make sure you do not have any leaks or blockages. If so, that can cause the car to think it is running lean and dump more fuel into the system.

    If you are not getting a "check engine light," it likely means all your sensors are at least working.
    2018 Subaru Crosstrek, 2014 Audi Q7 TDI, 2013 Subaru Forester, 1969 Chevrolet C20, 1969 Ford Econoline 100, 1976 Ford F250
  • doctordbonedoctordbone Member Posts: 3
    yea sorry i meant wires and plugs. if one of the cylinders isnt sealing properly will that be a pain in the [non-permissible content removed] to fix? and yea i don't have any check engine lights so i believe my sensors are ok.

    Do you possibly know how to do a compression test or should i look it up online? ive just spend a good deal of money on this car and would rather do everything myself. Oh and also i just replaced the alternator, idk if that has anything to do with the fuel consumption but it doesn't seem to be helping what so ever. I have a 13 gallon tank, which looks beat up as if someone hit it when running over something so lets say i have a 11 gallon tank. just recently i was able to get about 210 miles out of it. it was a lot worse before the tune up and the lucas injector cleaner. And the 210 miles were basically all highway so im pretty sure im getting garbage for mpg
  • rebel71rebel71 Member Posts: 87
    I had a 95 Impreza 2.2 L auto. I agree that the oxygen sensor should be looked at. I had to replace my oxygen sensor and ECU unit, this should help. Another thing to look at is the PCV valve and air filter. At 38,000 miles I had to replace an "O" ring because it was leaking oil. I realize every vehicle is different and you may not experience the same things as I did. Hope it helps. I had my Impreza till 2004 and 83,000, it was a great car.
  • ateixeiraateixeira Member Posts: 72,587
    I'm pretty handy but I think I'd get a mechanic to perform that test for me.

    I believe you put the cylinder at TDC and slowly add pressure to see what it'll hold.

    It's not going to be too easy because of the tight clearance to where the spark plugs are.

    This will tell you if the gaskets are failing and leaking, though.
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