Mercruiser 350 mpi issues again

[QBhoy]

Hi. Engine is a 2003 350 mpi and B3’s.

popping lean at full throttle and only getting to about 4000 rpm.

New cap and rotor
new plugs
proved fuel supply with using remote tank and still doing it.
no faults logged on rinda and fuel pressure fine sitting running at dock.

thinking best case fuel pump or fuel regulator blocked/ignition issue or worst case a sticking valve ?
any ideas ?

this has always occasionally popped a little but used to see 5000 rpm most times. Now nothing like that. Previously made it run better with a fiddle and slight turn of the distributor but not now. It’s still in the right position and aligned for ecu to control timing.

Thanks.

 

[alldodge]

To much WOT and no inconel valves, and your probably running a tad to lean
I would suggest a leak down test

 

[Scott Danforth]

fuel pressure?
compression results?

 

[QBhoy]

To much WOT and no inconel valves, and your probably running a tad to lean
I would suggest a leak down test

It’s not getting to full throttle AD. 5000 rpm is what it ran at before, but had the occasional pop. It’s definitely running lean. No doubt about it. Its been a problematic engine this, for years.

in case you’re wondering...it’s not my engine

 

[QBhoy]

fuel pressure?
compression results?

Fuel pressure hasn’t been checked when it’s up the rpm and on load. Only at idle abs higher rpm in neural apparently. The Merc dealership guy had it plugged in.

im beginning to think it may have a sticking valve. It’s had water ingress previously.

 

[QBhoy]

fuel pressure?
compression results?

Compression test getting done tomorrow.