115 Mercury EFI. SN 1B252422 Ran yesterday. Won't start today.

[RandyJ]

Went and picked up this pontoon yesterday. Started right up but ran rough. Coughed and stumbled up to 3500 rpm then would die down if I gave it more throttle. It had near a full tank (21 gallons) of gas that had been sitting there over winter if not longer. I put a full can of Seafoam in it then took it out for a ride and burned half the gas. At first it would run really rough but the longer I ran it and petted the throttle the better it ran. Never totally cleared up but did finally get to where it would run 5200 rpm with a few coughs now and then. Today I got in it expecting it to start right up with no problem.... cranks over fine but even after cleaning spark plugs it just back fires now and then and will not start. I checked fuel filter and it appears to be clear and fuel runs through it with no problem. Here's some before and after pictures of the sparkplugs. I used a wire brush, soaked them in starting fluid then gave them a couple of rounds in my ultrasonic cleaner. I'm out of cheap options... anyone got suggestions on what to do next?

 

[Ibl0wstuffup]

Is fuel getting to the carbs? Are the plugs all sparking? If it's backfiring I would check for spark and then check the timing.

 

[RandyJ]

EFI = electronic fuel injection (no carbs). Haven't checked fuel rail pressure but there is pressure on the fuel rail... appears to be good pressure.

 

[CharlieB]

It may be possible the spark plugs are fuel fouled and no amount of cleaning short of sand blasting, will recover them.

Have you pulled the plugs again and are they again wet with fuel? If so, install a fresh set and see if that cures your problem.

 

[Natesms]

I ran into the exact same thing with a 2008 Merc 115 EFI on a new-to-friend boat yesterday. It had been sitting for who knows how long. Thought we were going to have to get towed back.

I've done some reading and I've seen a lot of recommendations to clean the injectors. I also read over and over again about cleaning the VST filter on Mercs and Yamaha, however I'm not sure if this applies to this motor yet.

Keep us posted with what you try and I will do the same.

 

[RandyJ]

From the symptoms and how it acted when it did run I suspect water or moisture in the tank where high pressure fuel pump is located and possibly a filter in the tank. It may be a couple of weeks before I have time to get it on a trailer and tear into it. I'm sure cleaning injectors would help but I'm looking at fuel delivery first.