250 EFI help

I am a marine mechanic by trade but have run into a problem with this motor. It is an 1997 250 hp efi model S250TXRW. It had a hole between #1and #3 cyl. on the inter crank case side of block. all bearings, rods were in good shape. I thought mybe bad casting? But now to problem, the new power head when installed boggs at off idle and up. I checked fuel system all filters(clean) and high pressure pump (39 psi) replaced. All ignition checked ok, good spark. timing is at start up at 8 deg. before tdc and with increased throttle timing decrease. With all checks manual saids to do only the engine temp. sen. , O2 sen., and air temp. sen. are bad. Would all three of these things make timing off.
thanks for all the help.

[boats.net]

Replace the O2 sensor, It's probably bad but with a new powerhead you should replace it. Make sure draw tube is clean.

will O2 fix timing?

250 efi

I have a 2001 225 efi that had the same problem .The engine just would bog down on acceleration. It was traced back to the main wire harness.