P0308, Bad Compression

Discussion in '2011+ Mustang GT 5.0L Tech' started by brendan127, Aug 31, 2018.

  1. brendan127

    brendan127 Junior Member

    6
    0
    It has 25psi compression, and 99% leak down on #8.

    So what is needed to fix the car when it drops #8? I was quoted $9800 from brenspeed to fix it and I'm not interested in going that route, because I want to trade the car in at some point.

    Is it able to be fixed by just replacing the rings, and maybe the piston? If the cylinder wall is bad couldn't that just be sleeved?
     
  2. stkjock

    stkjock ---- Madmin ---- Staff Member S197 Team Member

    36,777
    395
    motor needs to come out and be rebuilt


    if you can do a swap, finding a junkyard motor would be least costly way
     
  3. weather man

    weather man Persistance Is A Bitch S197 Team Member

    13,124
    20
    Fleabay motor swap be cheapest.
     
  4. brendan127

    brendan127 Junior Member

    6
    0
    But why? What's keeping it from just being able to change the rings? Because it runs fine aside from pouring smoke out.
     
  5. brendan127

    brendan127 Junior Member

    6
    0
    A junkyard motor is still 4-7k which is too much.
     
  6. travelers

    travelers Senior Member

    2,925
    59
    It could also be valve seals.
     
  7. brendan127

    brendan127 Junior Member

    6
    0
    Bad valve seals on a 27k mile 2012 mustang? That's known for #8 to go bad?
     
  8. LarryJM

    LarryJM forum member

    189
    6
    I have seen some bad #8 pistons and they do look sad. What?? white smoke, black smoke, blue smoke? Truck engines seem to be 1/2 Mustang engines at junkyards. I found a 10K mile example for $2000. For sure it can't be fixed in the car.
     
    Last edited: Aug 31, 2018
  9. stkjock

    stkjock ---- Madmin ---- Staff Member S197 Team Member

    36,777
    395
    I guess thy could possibly pull the rod and piston from the bottom, but it’s rare that it can be done
     
  10. Gabe

    Gabe Whippled Coyote

    6,909
    205
    Built short block ...


    Screenshot_20180831-205652.png
     
  11. travelers

    travelers Senior Member

    2,925
    59
    Yea on second thought the compression wouldn't be low. Brain fart......
     
    brendan127 likes this.
  12. Marble

    Marble forum member

    682
    15
    There could be all sorts of carnage and until its torn down you will never know. I thought I had only a bad thrust bearing, but the bad bearing ended up toasting all but one rod. The crank shifted and ruined the block... etc etc.

    Point being you never know what is really wrong until its torn down. By going the route of only replacing rings on #8, I would almost guarantee the cylinder needs honing and ot would not work. Cheaper would be more expensive in the long run.