gas issue
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HT4100 4.1, 4.5, 4.9 Discussion, gas issue in Cadillac Engine Technical Discussion; I have a 86 sedan deville 4.1L engine and I was wondering is there a way to save on gas. ...
  1. #1
    still_walkin's Avatar
    still_walkin is offline Cadillac Owners Connoisseur
    Automobile(s): 1993 Cadillac deville sedan
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    gas issue

    I have a 86 sedan deville 4.1L engine and I was wondering is there a way to save on gas. Also I was wondering if there is a difference in regular super unleaded or supreme gas. Does any gas have an advantage or disadvantage to to the engine. Which one is better. If anyone knows any tricks to improve my 12/15 mpg issue let me know cause I'm not selling my cadillac

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  3. #2
    behind-bars is offline Cadillac Owners Connoisseur
    Automobile(s): 93 Sedan Deville 4.9L
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    Re: gas issue

    Check your oxygen sensor, If you havent replaced it recently, like within 40K miles I would do that first. Its cheap and somewhat regular maintenance. Then run the diag for any codes and address them.

    Use high grade gas unless you retard the timing back to 6 or 8 to allow you to run 87. I think any performance gains/loss is negligable. However if you run 87 without retarding the timing and you hear the engine knock it is harmful, still can be harmful even if you dont hear it.

    May also look into other tuneup items such as plugs/wires if applicable. Oh and make sure you are using delco plugs, one bosch mixed into mine cut about 1mpg off till i switched it out.

  4. #3
    still_walkin's Avatar
    still_walkin is offline Cadillac Owners Connoisseur
    Automobile(s): 1993 Cadillac deville sedan
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    Thread Starter

    Re: gas issue

    Yeah I was using the high grade gas till I passed smog which I'm gonna do this monday. So how much does an oxygen sensor cost. Also how do u retard the timing back so I can use 87 grade gas. Thnks a lot

  5. #4
    behind-bars is offline Cadillac Owners Connoisseur
    Automobile(s): 93 Sedan Deville 4.9L
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    Re: gas issue

    Quote Originally Posted by still_walkin View Post
    Yeah I was using the high grade gas till I passed smog which I'm gonna do this monday. So how much does an oxygen sensor cost. Also how do u retard the timing back so I can use 87 grade gas. Thnks a lot
    I have a 4.9 which is a bit different, The o2 is about $20 at any autoparts store and is similar to changing a spark plug. It should be screwed in the exhaust manifold under the hood.

    Thier are instructions on how to set timing under the hood and around the forums, I have never done it personally myself though and dont have a 4.1 to look at and see. It is probably 10o now, most people say 6-8 degrees to run on 87 octane. Basically you rotate the distributor ( if the 4.1 has it?) back just a tad.

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