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Thread: XJR lacking performance

  1. #1
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    XJR lacking performance

    XJR X350 2003.
    My XJR cut out recently after loosing revs. Couldn't restart it. Eventually got it running again and got home. No engine light and no codes. My wife has used the car locally and no repeat issues. However I can only describe it as feeling like I am driving through treacle;lack of power. Just connected up my cheap elm 327 scanner. No fault codes. I did check fueling pressure it said 54-56.
    Had a look under the bonnet of air leaks or anything obvious. Couldn't see anything obvious, not that you can see a lot of anything.
    Any one got any ideas?
    Thanks in advance

  2. #2
    Senior Member Alec Escolme's Avatar
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    Blocked cats possibly?
    Super V8, X358 Facelift + Portfolio Vents + Wald Spoiler, Black Cherry with Ivory/Charcoal leather + Black SuedeCloth Headliner, Rear Entertainment, Picnic Trays and Split Rear Reclining Seats. 200 Cell Cats, 2.5 SS Custom X-Pipe Exhaust, JagDroid Headunit, Arden Sportlines with 295 rear
    BMW 650i LCI Facelift, Convertible, Black Saphire with Cream/Black interior
    Ex. XJ X350 3.0 Silver/Dove

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    Block cats? Interesting. Apparently exhaust vapour should feel hot. Will try this

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    Senior Member Alec Escolme's Avatar
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    Super V8, X358 Facelift + Portfolio Vents + Wald Spoiler, Black Cherry with Ivory/Charcoal leather + Black SuedeCloth Headliner, Rear Entertainment, Picnic Trays and Split Rear Reclining Seats. 200 Cell Cats, 2.5 SS Custom X-Pipe Exhaust, JagDroid Headunit, Arden Sportlines with 295 rear
    BMW 650i LCI Facelift, Convertible, Black Saphire with Cream/Black interior
    Ex. XJ X350 3.0 Silver/Dove

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    Senior Member Clifton94's Avatar
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    When was the last time you replaced the fuel filter
    2007 xjr portfolio / Lexus IS 200

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    anything related to fuel pressure or supply would have given you a fault code.

    I would check the crankshaft speed sensor first - if that's partially open-circuit, the car won't know its actually running

  7. #7
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    I changed the fuel filter about 3 months ago, after I had over fueling issues. In the end I changed fuel pressure sensor which cleared code.

    Would a bad cat likely throw up a code? I suppose not in the case of the thread above. Crank sensor would be worth a look.

    Thanks for all your help

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    The fuel pump(s) are run on a demand basis - if the fuel rail pressure sensor is not seeing the pressure that it expects considering how hard the pump(s) are being driven, then you get a code and I'm assuming a restricted performance.

    "Bad" cats don't really exist for these - they're very stable metal-substrate cats

  9. #9
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    I did have a random cutting out issue a while back, which combined with park brake problems led me to re-wire from the rear under-seat to the fuel pumps, park brake and ABS sensors and height potentiometers

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    Senior Member Stagnite's Avatar
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    Quote Originally Posted by Alec Escolme View Post
    Fascinating, what an excellent thread.
    Currently enjoying:
    2007 XKR Convert. Frost Blue, Ivory leather. 32k
    2006 S Type R. Slate Grey, Dove Grey leather. Full Burr Walnut upgrade, Rear DVD screens. 64k.
    1999 XKR Convert. Meteorite Silver with Ivory leather. 79k.
    Previously enjoyed: 1970 XL6 4.2 1974; 1982 XJS HE V12 5.3 1987 - 1990; 2000 S Type 3.0 manual 2001-2015; 1998 XK8 Convert Mar/Apr 2016. 2009 Red XK convert Nov 2016 to March 2017: 2010 All black XKR May to Oct 2017: 2009 Green XKR convert. 28k miles.Mar to July 2018

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