2008 Mercury 90 EFI

[bamaegghead]

I have recently purchased a 2008 Mercury outboard 90 HP EFI (4 stroke) that had sat for several years. It first cranked and ran without any problems. However, after getting it out it seems to stall out idling witnin 5 minutes or less. I have run a full tank of 100% gas with seafoam in it. At times it looses power with a WOT and other times it runs awesome at WOT. But going back to idle it always stalls out. I can take the filter off the high pressure side and let the fuel pump prime (no bulb) it again it will be ready to go again. When you first crank it and let it idle it never stalls out until after running it. I have put new fuel filters on it as well.

Anyone have this problem or ideas?

Thanks!

[Rudebob]

Had a similar problem. Bought a boat that had a newer motor that sat for several years. The seller spent like $1,500 dollars to get the boat ready for sell which included basic motor tune up along with replacement of gas tank and all external fuels lines. The boat ran great first trip out. Soon got to the point it would not idle and cough a bit under throttle. Finally, it would not start at all except with starting fluid. The problem was the fuel lines inside the motor were original, and though not exposed to the elements, also chemically broke down from long term exposure to fuel that likely had MTBE in it. The carbs were loaded with little chunks of rubber. Cleaned the carbs and replaced the lines and that boat ran like a champ until I sold it. One possibility to look into.

'bob

[kryptonite]

If you have a portable gas tank, try running it from it to eliminate any tank issues. If it runs good sometimes it seems it would be something in the delivery system.

[wwind3]

I have a 2009 90 Optimax 2 stroke that broke down on me 4 times in 4 yrs---after 1st time rplcd fuel line replaced fuel pump grommet? and ran additives with every fillup. Finally idiot dealer after I TALKED TO HDQTRS in Fond du Lac(we are on first name basis now) and found out it was a rubber fitting in fuel pump(have 2 fuel pumps I think) that there was a bulletin on it and a fix. Whooda thunkit?

Knock on wood it still runs good so maybe have your fuel pumps checked--the starving prob with fuel may indicate bad fuel pump. Good luck.

[bamaegghead]

Ok I hooked a external tank up to it and seems to run better but still stalling out just not as quick. However, after running it for several hours now you cannot hear the fuel pump engage and it will not crank. I also get 6 beeps from the switch now. So bad fuel pump? or lift pump?

[Averyps]

I had the same issue with my 90 merc 4 stroke. Merc dealer replaced the internal fuel float with the upgrade system. Runs like a new one again

[justrfb]

Hello.
I had similar issues with my 2007 Merc... It was the fuel pump. After fixing that, runs like a CHAMP!! Good luck...

Sincerely,
Rich

[bamaegghead]

I replaced the fuel pump and fuel float (Mercury dealer advise that). Runs great now just expensive. Thanks for all the help!

[wrd1972]

Which fuel pump resolved this?

[FLOUNDERPOUNDER225]

Here is the problem, this one was from ethanol fuel that had sat for a long time, gathered water and corroded everything in the VST (Vapor Separator Tank) that's where the pmp and float are located.