OK, 1993 150 XRi ate #4 cylinder

[ufm82]

From the scoring on the walls it looks like the cylinder went super lean and it wiped out the walls. Piston has an eaten away section right by the port. Compression was 115 across the board but #4 was 20. Engine lost RPM on the water and then quit but started back up and ran on 5 for a few seconds before I shut her off again. No oil alarm but if this were an oiler failure wouldn't it have killed all the cylinders? Top and bottom holes look fine. Haven't pulled starboard side head yet. My question- what caused this?

UFM82

Engineless

 

[Chris1956]

Not likely an oil injection failure, as all the cylinders would be affected. Probably the main jet for that cylinder is clogged, or some other lean causing issue.

 

[Faztbullet]

My question- what caused this?

Injector problem,ECU problem,trigger,switchbox,advance module...