[Dave at Pelican Parts]

My 2.0 hydro-locked on me once. A bad ECU was causing way too much fuel to get dumped into the manifold. It was so much, in fact, that it wound up being more than the volume of the combustion chamber when the piston was at TDC.

Fuel (by itself) is not very compressible. Stopped the starter cold!! Didn't bend anything, happily. I cleared it by pulling the spark plugs, disconnecting the coil, and cranking the starter. I'm told fuel shot up in the air about 15 feet!!!

I'd try that. I'd also remove the valve covers and look to see if anything is obviously different about one valve.

Not sure what else I'd try offhand.

--DD