Audizine - An Automotive Enthusiast Community

Results 1 to 6 of 6
  1. #1
    Registered Member Two Rings my_01_S4's Avatar
    Join Date
    Jun 20 2007
    AZ Member #
    18960
    Location
    Silicon Valley, CA

    Unhappy low compression... possible causes?

    Guest-only advertisement. Register or Log In now!
    Low compression in 3 cylinders. 125, 90, & 90. Any idea's on most likely causes? Mechanic thinks for best case scenario a few valves are burnt (yes, he's trust worthy) but it could be something worse of course.

    W/ my limited engine knowledge, I don't know of a way to tell if its the valves or something else. Is there any way to tell with some degree of certainty without doing a full r&r? Asking so I can to determine the cost of this repair.

    Dang I wish I knew this was gonna happen before I just had my timing belt done last month since they're gonna have to undo all that work!

  2. #2
    Registered Member Four Rings ThirdStrike's Avatar
    Join Date
    Nov 17 2006
    AZ Member #
    13467
    My Garage
    b5S4, mk4GTi, 8pA3
    Location
    N Las Vegas

    Re: low compression... possible causes?

    125 is not low. 90 is.
    lets hope you didnt do this; http://www.audizine.com/forum/showthread.php?t=224547
    besides doing a leak down theres really no way of telling where youre loosing the compression without pulling a head off.
    just cross your fingers its not a piston ring
    00110100011100100110100101101110011001110111001100 001101000010100000110100001010
    |K04|Eurodyne Maestro|E85|426awhp/447awtq|No bitchassness|

  3. #3
    Veteran Member Four Rings S4 in_lowplaces's Avatar
    Join Date
    Feb 09 2006
    AZ Member #
    10187
    My Garage
    2001 Stg 3 Giac s4, 2000 Stg1 S4 APR, 2000 Stg2 S4 revo. All silver
    Location
    Huntington Beach

    Re: low compression... possible causes?

    i wuld say 125 is low. my compression was between 170-180
    Mooseimage - I'm no longer afraid of needles since I was like 10 (I used to be the kid that 5 doctors and my mom would have to hold down while another doctor stuck me in the ass.) Now I actually really enjoy it and watch

    Redline Redline's Response - might want to have read your words more carefully...

  4. #4
    Veteran Member Four Rings AudiA4_20T's Avatar
    Join Date
    Oct 29 2005
    AZ Member #
    8553
    My Garage
    '04 A4 Cabby
    Location
    San Francisco, CA
    Items for Sale

    Re: low compression... possible causes?

    Quote Originally Posted by my_01_S4 View Post
    Low compression in 3 cylinders. 125, 90, & 90. Any idea's on most likely causes? Mechanic thinks for best case scenario a few valves are burnt (yes, he's trust worthy) but it could be something worse of course.

    W/ my limited engine knowledge, I don't know of a way to tell if its the valves or something else. Is there any way to tell with some degree of certainty without doing a full r&r? Asking so I can to determine the cost of this repair.

    Dang I wish I knew this was gonna happen before I just had my timing belt done last month since they're gonna have to undo all that work!
    leaky valves or bad rings
    - Clint

    Newest: 04 DG B6 Cabby 1.8T - stock forever
    Gone: White '04 S4 2.7T - Stage 2+
    Gone : Fastest B6 A4 ever - 464awhp/12.1@116
    Gone : 05 DG B7 2.0TQ - Stage 1

    Not a fan of the AZ Classifieds? Tell Anthony here: http://www.audizine.com/forum/showth...assifieds-suck

  5. #5
    Forum Moderator Four Rings Daft's Avatar
    Join Date
    Feb 17 2004
    AZ Member #
    620
    My Garage
    Stg 3 '04 A6 2.7T, 00 A4 2.8Q
    Location
    Bowie, MD

    Re: low compression... possible causes?

    I agree that 125 is low.

    Standard Specs:

    Allowable compression range= 130-188.5PSi
    Wear Limit= 101.5PSi
    Max Allowable Difference Between Cylinders= 43.5PSi


    As for the OP's issue, it usually boils down to the rings, valves, valve seat, valve guides or head gasket.

    Basically anything that creates and holds the seal on the combustion chamber. Running dangerously lean for long durations of time will soften and warp metal parts. This also will included the head gasket. Overheating the engine due to a bad thermostat or waterpump would also warp the head and cause the headgasket to leak.

    As opposed to engine internals leaking, a faulty headgasket would be indicated by oil/coolant mixture, sweet smelling exhaust fumes and even steam rising from the engine in areas surrounding the heads.

    If you want to get a better picture of what has happened here, there are two things you can do:

    1. Compression leakdown test with a smoke machine(pressurize cylinders to measure the loss over time and smoke to see where it may be exiting from)
    2. Borescope (send a video camera or sight glass probe into the chamber via the spark plug opening and see if the valves are fully seated at TDC)

    These might give you a better idea of what happened before you take anything apart.
    Brett - Moderator
    Issue?: email me.
    _____________________
    Stage 3 2004 A6 2.7T 6M

  6. #6
    Registered Member Two Rings my_01_S4's Avatar
    Join Date
    Jun 20 2007
    AZ Member #
    18960
    Location
    Silicon Valley, CA

    Re: low compression... possible causes?

    Thanks all.

    OK, I guess I need to find a shop to diagnose it using a borescope or do a leakdown test w/ a smoke machine.

    I'm confident it's NOT a head gasket as I've been exceptionally cautious about keeping her cool / at normal operating temp.

    Just curious if anyone knows the probability that it's the rings versus the head gasket/valves? I'm hoping gasket/valves are the more common cause... (because I don't want to have to mess with rebuilding the engine which I'd have to do if its the rings).

    Oh, before I forget, has anyone done a diy for doing either a head gasket / piston ring r&r / valve job on this engine? I checked the Audi DIY site but one hasn't been documented there.

    TIA.



Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


    © 2001-2014 Audizine, Audizine.com, and Driverzines.com
    Audizine is an independently owned and operated automotive enthusiast community and news website.
    Audi and the Audi logo(s) are copyright/trademark Audi AG. Audizine is not endorsed by or affiliated with Audi AG.