1999 250EFI losing rpm

Howdy!

I'm a long way from a service center, currently 20 miles off the coast of Belize, so I either fix this or fly in a mechanic. I'm really hoping you guys can give me some clues. Port engine suddenly loses rpm. Sometimes it revs right back up. Sometimes is dies. When it dies, it always restarts. This happens randomly and I can't cause it on purpose. Checked fuel issues and didn't find any problem there (strbd engine does not have this problem). My only clue is that this seems to happen most often in rough water at rpm of about 3800 and up, when the boat is pounding. Like something electrical, bumps loose, engine nearly dies (or does die), and then bumps back to life on the next few waves. Typical runs are 1-2 hours and it may do it 3-4 times or not at all. If you catch the rpm loss in time, you can sometimes throttle back to about 1500, wait a second, and then throttle right back up.

Up till now, this has been a nuisance but now, port engine won't start. Checked fuses and checked and cleaned every electrical connection in the engine I can find. No corrosion on any of it. While going through the connections and trying to get it started, there were times when it would and would not tilt, would and would not fire, would and would not turn over (no starter engagement). It's like there are suddenly multiple electrical issues but that just doesn't seem to make sense either.

I'm really stuck. Any body have any ideas?

THANKS!

Until you got to the part about it not starting it was sounding like a fuel pump problem (and there may be one that is unrelated to the electrical phantom).

The T/T gremlins and the fire/no fire kinda points at a harness problem. Bad connector, pinched cables somewhere between the motor and the helm.

Is your trim switch and keystart part of your shift controls or are they mounted separate on the dash? Could be some pulled/corroded wires under the dash.

Howdy!

Trim switches and keys are separate from shift. Engines also have a tilt switch on them. When it's dead, it's all dead, engine switch and dash switch. Walk around doing something else and it's hot again when you try it. This stuff drives me crazy.

Since you have a trim switch on the motor itself, disconnect the harness when it acts up. If it works fine from the motor end switch, then you can (kinda safely) say that the problem is either the harness itself or under the dash.

Vice-versa, if that makes no difference then the gremlins are under the hood.

This big EFI's are not something I work on often but I'm really having a tough time trying to figure what single point of failure could cause all your symptoms..