obnoxus

yeah,,,,Id be doing compression and leak down on that cyl next,,,,, have an inferred gun by any chance,,,, check header pipe temps between cyls

vintagespeed

swap known-good coil, if the problem doesn't follow the coil ur gonna have to dig deeper..

FIXX

So what was it?????

BUP

All MPI marine engines with ECM or PCM controllers you do not ground a spark plug to check for spark. Sorry guys - factory OEM marine schools warns you about this for a couple reasons - one is a spike back to ECM could happen knocking it out or related ignition components and the big one, open spark in a engine compartment and gas fumes especially on a hot day = KABOOM. - it happens yes it does seen a couple of the after effects - 2 boats and 3jetskis.

A couple of years ago some techs did the exact same thing at a marina in Dallas and burned down a few boats and half the wing in the process. They were checking for spark exactly grounding out a spark plug against the block.

the way to check spark is with totally sealed inline spark checkers. Buy 8 of them and it will help to see or not if you have fire while cranking and or running the engine. Hopefully this post will save someones boat and or their life. You never know when gas fumes are involved especially in very hot weather.

I hear you about checking for spark in a marine app, "done that for 30 years and never had a problem". Good luck because 31 years might be your last.

Allicat38

I agree with the plug under pressure not firing. swap plugs and try.