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Thread: Gas Mileage... Low! What's Everyone Else Get?

  1. #1
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    Gas Mileage... Low! What's Everyone Else Get?

    I have been getting much lower gas mileage than desired, about 8 US miles to the US gallon. That's about 1/2 of what I would expect...

    What is everyone else getting?

    It's an 1995 XJS with the 4.0L AJ-16 engine.

    Any thoughts on where to look first to improve?

    - No leaking gas into the trunk or under the car

    - Changed Air Filter & Oil / Filter recently

    - Runs good

    Thanks for the suggestions in advance.

    Rocky

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    Senior Member rick_shape's Avatar
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    Rocky,

    Same engine but different car...

    In my 1996 XJ 4.0 Sovereign LWB I'm getting around 22 mpg (Imperial Gallon) on urban mileage.

    On a long cruise at 70 mph I'm getting up to 28 mpg.

    Have you tried using a fuel additive such as Cataclean etc?

    Rick
    1996 XJ 4.0 Sovereign LWB. Titanium grey / Regatta Blue leather 134,000 miles and rising.
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    What are the emissions like? Is it running rich or not.
    The ECU temperature sensor can fail on these engines.

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    Senior Member rchiv's Avatar
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    As above is it running rich. Also check your brakes are not binding. They only have to bind a bit to drastically reduce fuel consumption. You can easily check this by taking a drive and when stopped feel each wheel carefully as a binding brake can make the wheel really hot. I cannot remember if the XJ has inboard rear brakes in which case the rear wheels will not be hot.

    Roger
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    Thanks, all for the good suggestions.

    I will start with the basics, and see what I find. The brakes tip is a good one, and probably the easiest to check. My car has the outboard brakes.

    I was thinking about changing the plugs (that will help me see if it is running rich). I was also going to check the timing if I can figure out how to do it (I have a service manual).

    Do these cars have an OBDII diagnostic port? Might be worth looking at.

    I am hesitant to take it to an emissions shop, as they typically send your results to the Department of Motor Vehicles (DMV). I don't want to get flagged as a "gross polluter".

    Anyway - thanks, I'll post up what I find.

    Rocky

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    You can do a first brake check by releasing the parking/hand brake and selecting neutral - the car should easily roll forward with a light push, or without if you are on a slope.
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    As I looked in my shop manual, it seems that the timing is set automatically with my fancy electronic distributor. Not quite sure about the OBDII reader - the manual discusses error codes, but the reader is called something else.

    Rocky

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    Senior Member Davidsw's Avatar
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    Check the plugs to see if they all look to be firing properly and while they're out do a compression test
    Jaguar XKR x150 Cabriolet 2010

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    Senior Member BigCatXJS's Avatar
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    AJ16 - if high mileage might want to replace the 2 Oxygen sensors. I did this on my '96 Daimler Six - gained a couple of mpgs. I bought some OEM spec ones from Britsh Parts.
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