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  1. #1
    Jr. Mechanic
    Join Date
    Oct 2009
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    Fairbanks, Alaska
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    Default 99 Yukon 5.7 No Oil Pressure Wont Start

    My brother has a 99 GMC Yukon. The symptoms were initially engine knocking sounds and low to no oil pressure. Made it home and now It won't start.

    Need help as soon as possible please.

    Thanks
    /***********************************
    2006 Chevy Silverado 5.3L Z71 Crew Cab
    Additions:
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    PIAA 520ions ( Mounted in grill now )
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  2. #2
    Legend
    stephan's Avatar
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    Sep 2010
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    Far West, Oregon USA,
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    Default

    Well there's no need to tell you how to fix your starting problems if it was knocking with low to NO oil pressure. You need to find out why there is no oil pressure & why it's knocking.

    It's either knocking because there is no oil pressure or,

    There's no oil pressure because the bearings are worn out.

    Both of these require dropping the oil pan. Drop the pan & pull the oil pump off first & see if the pressure relief valve & spring is stuck open causing the no/low pressure situation. Secondly I would take the pump apart and see if the gears are worn out. Before you pull the gears out of the body you need to scribe or mark them as these gears are indexed & need to be put back with the appropriate teeth matching each other if it is good enough to reuse.
    If it shows either of these faults Replace It. If the pump is bad you will need to pull some of the rod & main caps off & see if this has caused damage to the bearings & crankshaft. If it has post back & we will walk you through what to do next...

    edit*** in case you think you need to start it to check the oil pressure with a manual pressure guage, you don't. You will only do more damage by running it.
    Last edited by stephan; 10-31-2010 at 11:15 PM.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
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    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


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