C5 X7 HDi Fuel Pressure Problems
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  1. #1
    1000+ Posts Ken W's Avatar
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    Default C5 X7 HDi Fuel Pressure Problems

    Hi HDi Owners,

    For the second time I am getting 'Depollution Fault' alarms on the C5 X7. The first time was at 23860km and I got charged for a new Diesel filter and got told to only use Shell or BP diesel fuel. I have been using Shell exclusively since.

    I am getting the same symptoms now - big coughs from the engine when SWMBO demands a more than usual from the engine now at 39500km. I have attached the Lexia to it and it is reporting injection errors

    P0087 error Fuel Pressure Regulation Error - Pressure too low - 167 bar at 2000 rpm and

    P0088 error Fuel Pressure Regulation Error - Pressure too high - 1225 bar at 2700 rpm.

    Am I up for another fuel filter?

    Are these easy to change yourself?
    (It would appear so by Haynes if you have a 27mm socket.)

    Should I start to change them at 15000km as a routine?

    What do you think?

    Cheers,

    Ken W

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  2. #2
    Fellow Frogger
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    Not going to even try to offer a diagnosis - ask the dealer with the tools. However, it should be a fairly easy DIY job to change as long as you bleed it correctly afterwards, watch out for leakage when you remove it and don't damage the housing during the change. It would be an insert as opposed to the more expensive cartidge filters used on some other models. If you decide to change it yourself, you will be able to compare the old and new filters to see how much blockage exists.

  3. #3
    Fellow Frogger!
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    The fuel filter has nothing to do with high fuel pressure. Only if the readings are low, and then you would have trouble with bad running across the whole rev range. What you're reading is fuel rail pressure from the fuel rail sensor. Injector pressure is the same as rail pressure.

    Fluctuating rail pressure could be caused by two factors, the pressure regulator in the HP pump is either faulty or it's receiving misinformation [it's controlled by the ECU on the information from several sensors including the fuel rail] or it's a faulty rail sensor.

    A blocked filter will only cause a consistent low primary pressure at the HP pump. You can hear the in- tank pump struggling and the HP pump will therefore also struggle to make the scene.

    If your tank is very dirty, certainly change the filter if you like, but I would check/replace the short piece of wiring from the bottom loom connector to the fuel rail sensor very carefully. And check the fuse box connection thoroughly [follow the colors].

    Lexia readout is all very fine, but it's the interpretation of that information that defines the experience.
    Go Happy.
    Last edited by shanadoo; 7th April 2011 at 10:58 AM. Reason: misstake wrong info.

  4. #4
    1000+ Posts Ken W's Avatar
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    C5 HDi X7ers,

    Fuel filter is changed and I now have smooth turbo and power back with no errors.

    I ended up having to get a mechanic to do it because I couldn't get the plastic top to unscrew off the filter canister without feeling like I was going to break it. Haynes says to use a 27mm socket but apparently you need a single hex socket, not the normal double hex type. So I have now gone down to Tradetools and bought a impact wrench socket which is a single hex type. Haynes instructions were OK except for having to jump around the book a bit.

    Cheers,

    Ken W

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