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MFS30C 2015 top end issue

M

merc200dalarna

Contributing Member
At full throttle (or even at 2/3- cruising on plane) my motor has a tendency to intermittenly 'drop off'
Hard to explain, feels like fuel starvation.

It sort of 'alternates' between pushing hard, and dropping off for half a second, then pushing again for like 5 seconds and so on...

I have started to look at videos of 'injectors' and the 'VST' plus the many filters along the way.
And I have now learned that I should drain VST for winter.
I run on high quality '98 octane' european gas (5% ethanol)

Incoming fuelfilter was replaced this spring, no clogging or unusal debris.
New sparkplugs this spring.

I've had this issue and tried to use fuel additives like injector cleaner and quiksilver stabilizer, has sort of worked, or perhaps imagined to work..

Should I try to pull VST and check filter at HP-Pump? Plus clean out bowl and needle?
Or?
 
pvanv said:
It wouldn't hurt to clean the whole fuel system.
Click to expand...

Yes I'm set on doing so, but I found the high pressure filter, which I wasn't aware of, and it seems to be a 'one-piece'

(Perhaps I could gently flush it backwards with CRC carb and EGR-cleaner?)

Also, sorry for the delayed answer, but this forum isn't working properly when I use it from Sweden, Europe!

My next step is the VST-bowl and the filter at the bottom of the pump.

Thanks

BTW, what pressure read out should I have if I attach a gauge at the top of the fuel rail/injector rail?
 
pvanv said:
The WOT RPM is good. Sounds like you are misfiring; not ESG but an actual misfire.
Click to expand...


OK! Yes, I have learned to use proper props, here on the forum!! ( I have 3 props, this one is lowest pitch when we are 3 adults in the boat, still hit 22 knots)

First question on misfire: could it be a single cylinder misfiring? (Because I overfilled oil last year, cylinder 3 sparkplug was pitch black and moist from oil)
(I doubt corrolation, but I had that issue, and asked you this spring, and human, me, is often to blame)

Would such ignition trouble show up on tohatsu diagnostic, you think?

Edit: Thanks for taking the time to listen to the sound on that video, thanks PVANV!
 
pvanv said:
Possible. Check your plugs now.
Click to expand...
Been a busy week, but last night I went fishing and checked the plugs. The problem is found, lowest ("nr 3 cyl") had the plug pitch black with substantial build-up. And once again, somehow, oil level is too high. Damn, my fault. Thinking overnight, and I think I have not paid attention to have the engine hanging level when changing oil, because this spring I was careful to read and re-read the oil level throughout filling.

Edit: So, you are very likely right, it is a 'mechanichal'/'physical' misfire at the sparkplug with build-up
 
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