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Thread: Sudden drop in fuel mileage

  1. #1
    Supporting Member Turbo Mopar Contributor supercrackerbox's Avatar
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    Sudden drop in fuel mileage

    Within the last month or so, my Daytona has had a sudden drop in fuel mileage, to the tune of around 60 miles a tank. The car never got astounding mileage to begin with, but this is getting rediculous.

    No other real symptoms, aside from it's taken a little more cranking than usual to start on two occasions. The car seems slightly under powered, but runs well and smooth throughout the RPM range. No noticeable black smoke even under boost.

    I'm going to go over all the obvious stuff tomorrow- check/replace plugs, timing, filters, brakes. I've already checked it all over for fuel leaks.

    What else can I look for?

  2. #2
    turbo addict
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    Re: Sudden drop in fuel mileage

    Check for code, engine coolant temperature sensor, fuel pressure regulator, and o2 sensor.

  3. #3
    Hybrid booster
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    Re: Sudden drop in fuel mileage

    Also check tire pressure. Makes a bigger difference than most think. How old is the cat?

  4. #4
    turbo addict
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    Re: Sudden drop in fuel mileage

    I was going to say check your knock sensor and O2 sensor. I know replacing those on my Shelby Charger (when it was still a T1) really made a difference in my mpg.

  5. #5
    Garrett booster
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    Re: Sudden drop in fuel mileage

    I don't know. If it's having a little bit of a problem starting you might want to check the fuel pump and filter. does it still have the stcok bosch pump.

  6. #6
    Supporting Member Turbo Mopar Contributor supercrackerbox's Avatar
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    Re: Sudden drop in fuel mileage

    Pump is a Walbro 190, probably 3 years old now. Tires all have 32psi. I have checked the FPR recently, but I'll do it again. I know the O2 sensor is a bit older, so I've got a new one on the bench. Cat is still factory original, I hope that's not it. I think if it was plugged I'd be having other issues as well. The K&N filter was pretty (ok obscenely) dirty, it's drying right now, still waiting for the engine to cool before I get to the plugs and O2 sensor.

  7. #7
    Supporting Member Turbo Mopar Contributor supercrackerbox's Avatar
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    Re: Sudden drop in fuel mileage

    Well, results for the day. Plugs looked worn, but no signs of fouling, damage, etc. All evenly colored. No codes shown. But new plugs, new O2 sensor, clean air and breather filters, hopefully we'll have some results. Also the timing was at about 0 degrees, so I bumped it back up to 12. Last time I set it, I had it at 14 and she ran like a champ, but lately I've been having to buy a lot of 89 octane ethanol blend, so I'm gonna stay at 12. But right now I'm going to go fill it up with some 92 and see how she runs.

  8. #8
    turbo addict
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    Re: Sudden drop in fuel mileage

    A friendly mechanic at a local Firestone unplugged on of the sensors from the intake on my T1. It killed my mileage. The car still ran very well, but the mileage just fell off the map. I would recommended checking those connections and making sure something hasn't worked its way loose. I didn't even see the sensor was unplugged until I changed my O2 (I was headed down the route it sounds like you are taking).

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