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Sudden loss of gas mileage...What could be the cause?

Discussion in 'Tech Archive (No Posting)' started by daveskitz, Jan 13, 2007.



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  1. daveskitz

    daveskitz New Member 5+ Year Member

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    My '96 civic EX has been getting around 350 miles per tank full for as long as I can remember. All of a sudden in the last month or two I barely get 250. Driving habits have not changed and I was wondering what could be the cause of this sudden loss in gas mileage? I do not smell fuel and had garage check for fuel leaks but they found none.

    I did a major tune up including fuel filter but minus the pcv valve, which I will replace with next oil change; checked and fixed tire pressure, which was a little low 25 vs 30 fronts and 25 vs 29 on rears; the 02 sensor was replaced this past summer.

    The car is leaking oil but I'm not sure from where exactly but after steam cleaning the engine last week, I see oil under the valve cover and distributor.

    I did notice that when idling the car sometimes idles with a bit of a rough vibration. It kind of feels like when A/C would kick on but I'm not running A/C this time of year.
     
  2. AliasNeo

    AliasNeo New Member Registered VIP 5+ Year Member

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    could be the cold weather... its happened to me too lol
     
  3. JohnS.

    JohnS. BANGARANG Registered VIP Registered OG 5+ Year Member

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    First off, :welcome: ;).

    Now getting on topic, are you SURE you didn't leave anything out when you did a tune-up? Also, is your car throwing any CEL's? (You didn't mention you were hence why I'm asking).

    As for the idle, sounds like maybe a dirty IACV or something.

    The only reason why I personally lose MPG is because I put the gas all the way down too much.
     
  4. daveskitz

    daveskitz New Member 5+ Year Member

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    Never happened before in cold weather...
    and it's actually been pretty mild for this time of year so far.
     
  5. daveskitz

    daveskitz New Member 5+ Year Member

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  6. JohnS.

    JohnS. BANGARANG Registered VIP Registered OG 5+ Year Member

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    CEL = Check Engine Light. An orange light on your cluster that will light up if there is a problem. I'm assuming it's not on since you haven't mentioned it.

    As for the tune-up, what about fuel filter, O2 sensor (I know you said you changed it but you sure it's still good?), and fuel injector cleaner?
     
  7. daveskitz

    daveskitz New Member 5+ Year Member

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    Boy don't I feel stupid :oops: no CEL is not on.

    I did the fuel filter but no fuel injector cleaner...any recommendations on which cleaner to use? As far as the 02 sensor...CEL came on this past summer and it was determined by dealer that the 02 sensor needed to be replaced, so that's when it was done. How do I know if it's still good or not? Wouldn't CEL come back on if it were no good anymore?
     
  8. JohnS.

    JohnS. BANGARANG Registered VIP Registered OG 5+ Year Member

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    Oh yeah forgot you said you already changed it :smackself:.

    As for fuel injector cleaner, it really doesn't matter. Actually, you know what you should try? Seafoam. That helps A LOT. Especially with older cars that are dirty in the internals.
     
  9. iOn

    iOn I like pie. Registered VIP 5+ Year Member

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    o2 sensor? :what:
     
  10. Redbone

    Redbone Movin on up... Registered VIP 5+ Year Member 10+ Year Member

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    did you do the timing belt, water pump, tensioner change out too? That's an important step along the way. Also, did you get a valve adjustment?
     
  11. Szady

    Szady D-Series Master Registered VIP Registered OG 5+ Year Member

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    ..whens the last time you changed your oil? You didnt mention that you changed the oil w/your last tune-up. Old oil WILL give you bad gas mileage.
     
  12. daveskitz

    daveskitz New Member 5+ Year Member

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    Thanks I'll give that a try.
     
  13. daveskitz

    daveskitz New Member 5+ Year Member

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    Timing belt and water pump done about 23, 000 miles ago; not sure about tensioner. No valve adjustment done.
     
  14. daveskitz

    daveskitz New Member 5+ Year Member

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    Oil changed about 2 weeks ago.
     
  15. iOn

    iOn I like pie. Registered VIP 5+ Year Member

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    no one thinks o2 sensor could be a possibility? :what: might be causing you to run rich... it is a possibility if the usually tune ups do not improve fuel economy. vacuum leaks and ignition problems are common problems also.
     
  16. daveskitz

    daveskitz New Member 5+ Year Member

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    As far as the 02 sensor...CEL came on this past summer and it was determined by dealer that the 02 sensor needed to be replaced, so that's when it was done.

    How do I know if it's still good or not?
    Wouldn't CEL come back on if it were no good anymore?
     
  17. iOn

    iOn I like pie. Registered VIP 5+ Year Member

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  18. daveskitz

    daveskitz New Member 5+ Year Member

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    Brought the car to the garage and they said if 02 sensor was no good or a problem, then CEL would be on. Also said car soes not need valve adjustment. Iasked them to look more closely for a fuel leak and to check if the brakes are dragging.

    This is baffling me...
    Any other suggestions???
     
  19. Szady

    Szady D-Series Master Registered VIP Registered OG 5+ Year Member

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    Is there more weight in the car than you normally have? The extra weight will make the car heivier, therefor making the motor work harder, therefor using up more gas....
     
  20. daveskitz

    daveskitz New Member 5+ Year Member

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    Ocassionally a 200lb passenger + a wheelchair :lol: but other than that no.
     


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