low compression in 2 cyl. need advice

[ANVIL]

a little bit of background in this thread

rb25det-failed-pcv-valve-what-damage-co ... 99721.html

Short story of what happened.
-went out for street tune, felt boggy and misfire after a few pulls at 20-22psi. during session found valve cover vent tube blew off and oil leaking from valve covers
-found oil in ic piping. Found pcv to be bad. Leakying vc allowed spark plug galley for #5 to fikl almost completely with oil. Replaced and installed catch can. Also cleaned up all oil.
-still runs rough. Did compression test 1-4 @ ~155-165. 5 @ 90 6 @65

not sure what caused this. Leaky Pcv valve do enough to do this kind of damage? Or completely unrelated?

Prior to tune session it ran great at 18psi. i have a hypergear turbo upgrade which can stil make great power up to 24-26psi on my stock block/head. Was going to crank it up until this happened. All we really got to do was do a few pulls at 18psi to log and keep afr safe before adjusting ign timing. Did a pull at 20psi. Everything ok. 22psi pull is when it occured. I doubt the tune played a part in it, all we did was log abd adjust afr on the rich side.

sounds like rings ? Just old? Can i just get new rings and replace them for 5 & 6? Can valve seals cause this bad of a compression drop?

Now i need to decide on what to do and what is the next step to diag then fix this. All opinions and advise is apprcieciated

[Yellow4g63]

must have gotten some kind of knock to kill the pistons. or really high EGT's if it was really rich.

[ANVIL]

Nice to hear an OG chime in yellow4g63. forum is slow af these days.

You think it was the tune? Anything over 18psi was ununtouched as far as timing adjustment goes. Originally started with the power fc rb25 base map

[ANVIL]

Also i dont think it ran any richer than 10.5-10.8 at the most

[ANVIL]

Failed pcv with a bunch of pulls at 20ish psi wont cause this kind of damagE? cant remember exactly but i think it was maybe 6 pulls adjusting boost gain and also making sure afr doesnt lean

[ANVIL]

Also was monitoring knock on thr pfc and live reading from fcedit and never got any high readings. I dont remember exactly id have to ask my tuner

[ItzGenX]

It sounds like a ring land let go or the piston melted. Usually 5 and 6 run hot and lean since they are the last to get coolant, and they are at the end of the intake plenum where the high velocity air "dams" at the end. I usually run 1-1.5% more fuel on #5 and up to 2% more fuel on #6. I also retard -1-2 deg of timing during boost anywhere above 10psi on those two cylinders with my haltech since they are hotter. For the fuel trims, I just slowly add the fuel and do a long steady state cruise after cleaning all of the plugs. After the cruise, check and compare the plugs, add fuel to 5/6 until their plugs match 1-4. The % trim will be applied completely across the entire tune once the values have been determined base on setup.

You should be able to do a leak down test to determine if the loss of compression is either through valves or piston. Air leaking out into the block indicates the piston/ring setup is the culprit, and if air runs out of the intake manifold or exhaust, then it's a bent valve. By your description, it is almost always the piston since the massive amount of blow-by happened. That just means a lot of the combustion between 5 and 6 went right past the piston pressurizing the block and seals sending oil everywhere.