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Compression Test Procedure (petrol V8)

Discussion in 'Range Rover' started by markleb, May 22, 2012.

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  1. markleb

    markleb New Member

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    Hi all

    Had a small amount of oil when changing plugs (on two of the plug wells only) - so wanted to do quick compression test.
    I'm thinking it may just be a small leak in gasket, but want to rule out bigger probs.

    Is it correct that I should remove fuse for fuel pump and un-plug all coils before screwing in compression tester and turning engine over??

    Not done one before, but have the tester, just want to make sure have the correct procedure.

    Thanks in advance for any advice,
     
  2. fanatic

    fanatic RESPECT IS EARNED, BEATINGS ARE FREE ;-) LZIR Despatch Agent

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    throttle fully depressed and crank same time for each cylinder
     
  3. markleb

    markleb New Member

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    Thanks - I assume my other bits of the procedure were right too??

    Cheers
     
  4. jt_armstrong

    jt_armstrong Well-Known Member

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    Wont do any harm to remove the fuel pump relay. I have normally just disconnected all the HT leads at the plug ends. Make sure engine is warm and throttle is open when you take the reading. Do each cylinder dry and then squirt a bit of oil in and repeat the process. Expect to see a difference especially if the rings are worn.
     
  5. markleb

    markleb New Member

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    Cool, thanks for that, much appreciated.
     
  6. vougese39

    vougese39 Well-Known Member

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    4.4 engine oil leak in the plugs will proberly be the rocker cover gasket.
    You may get a engine fault due to cranking with plugs and coils disconnected and the fuel pump relay out too
     
  7. markleb

    markleb New Member

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    Thanks. I was thinking it was rocker cover gasket, hence the thought to do a compression test to rule out issues.

    Is there a better procedure, if how I plan to do it is wrong?

    Do you mean it will throw up a EML light? If so, I assume I can cancel this with my OBDII fault code scanner...

    Thanks.
     
  8. wammers

    wammers STILL BREATHING. Donater

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    Doing a compression test is quite a novel way of checking for a oil leak from the rocker covers. If you had oil in the plug cavities there is only one place it can be coming from. It won't be being blown up past the plugs that's for sure.
     
  9. markleb

    markleb New Member

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    Thanks, I'm not looking for novel ways to check anything, just trying to put my mind at ease.

    I'm no expert (obviously!) but had been told that it was best to rule out any other problems related to any oil by the plugs, other than the obvious gasket?

    I have no idea - just what I've been told/read :)
     
  10. rewmer

    rewmer Well-Known Member

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    As already mentioned, your oily plugs are due to a failed rocker gasket. Does it smoke at all ? And how is the idle? These two things can be a sign of a failed PCV valve on the back of the inlet manifold which can also lead to oil being forced through the gaskets.
     
  11. wammers

    wammers STILL BREATHING. Donater

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    If you had enough oil in the cylinders to blow past the plugs which it won't. You would be laying a smoke screen better than any WWII destroyer could ever manage. :);)
     
  12. markleb

    markleb New Member

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    No smoke, no idle issues. I assume just gasket then?
     
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