Hydrolocked? Stuck Piston? Driving me nuts, any help appreciated

[AngryNovice]

in the beginning the engine had codes it was running rich and some misfires. Replaced plugs and coils on 6 and 8. Replaced shredded vacuum hose, changed oil that was full of gas. It was hard to start and heavy white exhaust full of gas. Shut off changed rest of plugs and coils, listened to fuel injectors, all were ticking. Still ran rough and gas in Exhaust. Next day started it and engine sounded awful with a clanking so I shut it off. Checked plugs and changed oil again and next day it wouldn’t turn. Starter was dead so I replaced. Still wouldn’t turn so removed plugs and tried to hand crank it and it wouldn’t budge. Backed it off to see if starter could break through, it did and the engine turned. Ran compression test and all were okay but 6. It had ZERO compression. Running air into cylinder i can’t pinpoint where air is leaking, it floods out. Took valve cover off and springs are tight and all looks fine. Now when I manually turn engine it will turn a bit and hits a wall and won’t budge. Back it off and noticed when i put a dowel into cylinder when I am turning engine back and forth the piston isn’t moving. I’m sure engine is shot but I want to know what happened so I’ll have to have a look at the piston. Sorry for the length but it is what it is. I probably left things out tbh. Thanks in advance for any advice, this forum has been a lot of help and I’ve learned a lot.

 

[GlennSullivan]

Broken Rod. Assuming there was no bent or broken valve to cause this and a scope through the spark plug hole does not show damage / marks to the top of the piston. This, along with your statement of a lot of gasoline in the oil, I would guess that the injector in that cylinder hung open and (as you suggested), hydraulic-ed that cylinder on the compression stroke. That horrible noise you heard when running it after the event was the broken end of the rod still connected to the crank smashing the crap out of everything around it, until it locked the engine, possibly jammed against part of the lower end of the block.