Low Compression on 3 Cylinders - 5.7

[Mopar JP]

Hello Everyone,


I am trying to help a buddy out who took in a friend’s 2011 1500 with a 5.7. Apparently, the truck went into another shop initially for a valve job to remedy a misfire issue (not sure of the exact details of what was found to lead to that valve job). The timing chain and assembly were not removed, and cam and lifters were also not touched. Everything on the valve-train seems to be within tolerance, no excessive play, etc. Upon leak down, it was found that 3 cylinders had low compression as noted below:


· Cylinder 1: 70 psi

· Cylinder 6: 45 psi

· Cylinder 7: 120 psi


All other cylinders were within 10% of where they should be.


One thing that buddy did note before approaching me for advice is that the lifters on each of those cylinders appear to remain fully pumped up, and do not bleed off pressure. Not sure if this is coincidence that all of the low compression cylinders are those that are “shut down” during MDS operation, or not.


One of my thoughts for a cause is maybe the pistons were somehow damaged or holed during the initial issue that led to the valve job in the first place, but you would think that would be noticed. The heads have yet to come back off, as well as the intake manifold (not sure of the condition of the MDS solenoids).


Any thoughts on what might be going on here, before I go over this weekend to help figure it all out?

 

[KenR 955]

Seems like a leak down test is in order. Air noise in the exhaust= exhaust valves. Air noise in the intake = intake valves. Air noise in the PCV or block vent = rings. Could be other things too, I guess. This is how I would proceed tho.

 

[Nicholas Cove]

Ken is correct. Leak down test. Most likely the cam and lifters are wiped out.

 

[flyboy55]

Is factory still saying liter is not their fault?