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P38 gems 4.6 backfire/misfire sound

Discussion in 'Range Rover' started by Wesleyb69, Jan 11, 2017.

  1. Wesleyb69

    Wesleyb69 Member

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    Hi newbie and in need of help . Sounds a bit like a backfire which is most audible from the plenum
    New plugs
    New leads
    New coil pack
    Any help please
     
  2. brianp38dse

    brianp38dse Well-Known Member

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    Leads round the wrong way?
     
  3. Wesleyb69

    Wesleyb69 Member

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    Hi Brian had a similar noise before the the change of plugs etc , was told it might be worn cam , but the noise has no rhythm to it
     
  4. brianp38dse

    brianp38dse Well-Known Member

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    They can suffer from worn cams, pull rocker covers of and see if all the rocker move the same amount that will confirm cams.
     
  5. Wesleyb69

    Wesleyb69 Member

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    Thanks Brian, would a faulty rocker arm give the same noise?
     
  6. Tony e

    Tony e Well-Known Member

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    Sound more an electricory problem to me, could just be a simple lose contact, o the joys
     
  7. brianp38dse

    brianp38dse Well-Known Member

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    Rocker arm not moving as much would indicate a wore camshaft.
     
  8. Grrrrrr

    Grrrrrr Well-Known Member

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    Running LPG?
     
  9. Wesleyb69

    Wesleyb69 Member

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    No lpg there was no warning either it just started to make the noise
     
  10. Wesleyb69

    Wesleyb69 Member

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    Just found this after plenum removal IMG_0020.JPG
     
  11. Wesleyb69

    Wesleyb69 Member

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    Also some what looks to be like gold glitter in the coolant IMG_0019.JPG IMG_0021.JPG
     
  12. Doo

    Doo Well-Known Member

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    It looks awfully like coppaslip (or copperslip whoever manufactures it....) copper grease. But why would that be in the coolant?

    The only other thing that may resemble it is Radweld.

    However, a misfire since the plugs, leads & coils have been replaced could only mean one thing, one of the plugs (or more) isn't firing at the correct time!

    Pull out the plugs and check them, the gap, the insulator and so on. Did anyone drop a plug and close the gap or such like?

    As suggested, it could also be a mix up of the plug leads. Or worst case, a burned valve... But I would put money on plugs, leads or coils seeing as how they were just done and this just happened or a I reading it wrong and it happened leading to the replacing of all the above? In which case, burned valve if it's making a noise in the plenum.
     
  13. Wesleyb69

    Wesleyb69 Member

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    Hi doo hi do it was happening before hence why I changed them all
     
  14. Doo

    Doo Well-Known Member

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    Possibly cheapest & easiest thing to do 1st is a compression test, see if there is a vast difference between cylinders.
     
  15. Wesleyb69

    Wesleyb69 Member

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    I recorded this yesterday

     
  16. Doo

    Doo Well-Known Member

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    That really sounds as if it is exploding in the plenum chamber.

    So, how would it be possible for fuel to be burning in the plenum?

    Does it have knock sensor? Could even be continuing to run open loop, making it overly rich! Check O2 sensors, temp sensor and Throttle Position Sensor, which would all affect the fueling.

    Afraid I am not used to working on V8's, but any petrol that is misfiring does so for a reason.

    The timing is crucial on EFI engines, so everything needs ruled out.

    Did it come on slowly or all of a sudden?
     
  17. Wesleyb69

    Wesleyb69 Member

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    Hi it cam on suddenly
     
  18. Doo

    Doo Well-Known Member

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    You really need to get it on a code reader, or you'll end up tearing your hair out :confused:

    This may help build up a picture of how your system works in the meantime

    http://blackbox-solutions.com/help/SM001.html

    Check for splits on the pipework after the MAF sensor, as this will mess up the fuel/air mix if nothing, try unplugging the MAF and giving her a run. If the explosions stop, it possible that's the likely fault.

    However, I can't recall if you mentioned MIL (Management Indicator Lamp) lit up or not?
     
    Last edited: Jan 12, 2017
  19. Wesleyb69

    Wesleyb69 Member

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    Hi all bit of an update
    Compression test done all 100 psi
    Rocker cover off passenger side all seems to be rocking as it should
    With all plugs out still getting back pressure form cylinder 8
    Really confused now
     
  20. myfirstl322

    myfirstl322 Well-Known Member

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    Where's the pop corn emoticon?:D