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Outboard mercury problem


RD9

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Have a 115hp 2007 efi merc. Motor will run rough after trolling for awhile and the RPM's will occasionally drop off also at higher RPM's. will run for miles with no issues and then all of a sudden it will run bad again. Replaced two inline fuel filters and no difference. Fuel is treated. Any suggestions?

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Wow I have a 115 2008 merc, same problem. First thing I tried was stabilizer no luck, replaced both inline filters. Just last week my mechanic plugged into the computer, turns out 2 out of three fuel pumps were bad.. I should have told you to sit down before reAding this.

Also my air filter was completely disentegrated.. I had the exact same problem this year.. Let me know how you make out

Sent from my iPhone using Lake Ontario United

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I had similar problems. Replaced all spark plugs and replaced fuel filter and problem went away. I believe it was a bad plug or plug connection that was fixed when I replaced the plugs. Mercury 2004 115 efi. Good luck

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Well today I am going to put a new fuel line and see what that does mercury dealer said he would give that a try. The fuel line on one motor is two years old the motor that is not working correctly has the original. Dealer said doesn't think pump would be bad because it will run for long periods with no real problems. Who knows, just want to keep fishing. I will know later today and if no luck back to the dealer and out of the slip.

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Could be a carb issue? Buildup from low speed trolling and ethanol gas could cause that issue i would think.  if i troll on my 2003 125merc i will run it in at the end of the day on full throttle to blow off any buildup, or if not at least rev it up high in nuetral any never have any problems

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I have a 2002 Merc 115 4 stroke EFI. Twice threw the years I had a intermittent rough running condition. Like you I changed the fuel filters with out curing the problem. Both times the cure was a new set of plugs and presto.............runs like new. The plugs are pretty pricey,..... Cabela's had them the cheapest. I now keep a spare set of new plugs on hand and the next sign of a rough condition the plugs will be the first thing I change.

 

Hope that works for you guys. :nod:

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I changed the plugs and still occasionally drops rpm once over 4500 rpm. It occasionally will surge back up after a minor drop in rpm. Between 1500 and 4500 rpm everything is great, but still will run rough after trolling for ten minutes. Been fishing just taking it easy on it right now and will take her to dealer after first week of August. So far I have changed plugs, fuel filters and fuel line. Any more suggestions would be appreciated. I have dual outboards so i have been trolling with th other and just cruising out at 4200 rpm.

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I'm not real familiar with the mercs, but on a yamaha there is a component that is consistent with almost all efi engines and that is the Vapor Separation Tank and the related fine screen filter and high pressure fuel pump that are housed inside it. One other component is the oxygen sensor, but I believe your engine does NOT have that..not sure though.

A pressure Guage on the fuel rail will reveal injector feed pressures. The pressure should remain same throughout engine rpm and increase. If it decreased the pump may be on its way out....but not necessarily. The VST does what it's name implies. ..separate vapor from fuel to keep the pump from starving of liquid fuel. It does this by the fine screen inside the tank. If the fuel pressure drops your going to go inside the tank anyway but before you take out the pump check the screen for white film and debris.

All this is not as intimidating as it sounds If you have a manual and some mechanical finesse. It does require a spaghetti o ring seal to replace in the tank and care to get it back in without pinching it.

The pump is not cheap. The Yamaha runs about 340 bucks...merc probably follows that closely.

Here is something that I do each year you could try. It's called a seafoam shock treatment. I assume you have the 4 stroke. But this will work on an oil injected 2 stroke like my Yammy.

Find the fuel line going to the VST and unplug it somewhere in the line going to it from the fuel supply, usually after or even before an in line fuel filter on the side of the engine. Mix a full can of seafoam in a one gallon Gas can topped with non ethanol gas. Run a hose from the disconnected fuel supply going to the VST into the gas can mix. I hang the fuel can from a lenghth of electrical wire so its level on the side of the engine. Start the engine and let the mix run completely out at about 1200 rpm. After the mix runs out, let the engine sit for a couple hours and hook the fuel lines back up and start the engine and run it until it warms up and give the engine some quick throttle snaps to blow out any carbon. It will smoke white for a while but that will not hurt anything. As the mix works through the screening in the VST it will clean up the white film or debris in there. Also the combustion chambers and injectors will get a thorough cleaning. That may make all the difference in its throttle behavior next time out.

If not...and you still have pressure issues, then it's time to open the VST and clean the screen. If the screen is clean then the high pressure pump is the likely problem.

Marine mechanics love the VST issues so if you can do this stuff yourself you will save a few hundred or a 1000.

Hope this helps...seafoam is a quick easy fix for dirty injectors and fuel sytems.

Mark

cent frum my notso smart fone

Edited by skipper19
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Thanks for the response. I have read about the vst screen and I called mercury and they had a warranty claim of "cleaning vst" on other motor. I had the original fuel line connected on this motor and believe I probably have a fuel restriction in my screen.

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That's the beauty of having twins and one runs bad you can swap some things and see any difference. I would try that seafoam shock. It does a lot of good for the fuel system without the need to dismantle everthing. Afterwards it might run much better.

cent frum my notso smart fone

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Ok now I am confused. Did the fuel shock treatment while doing it ran boat at 1500 rpm, put it down to trolling speed were boat ussually stalls and it ran great no issues for an hour, so I assumed problem was solved. So today got back in motor is now hooked back up to boats fuel tank and now it won't troll. So with fuel line ran into a seperate tank 2 gallon can with non ethanol fuel it runs. Hooked to big tank and same problem as I previously stated occurs.

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  • 2 weeks later...

Your high RPM issue sounds similar to one i had on my merc optimax which isnt al that different from the EFIs. Intermittent issue with rpms dropping and coming back up, sometimes repeatedly and rapidly to the point it stalled out. Took 3 dealers to figure it out...turns out it was the high pressure fuel pump, which would only fail in high heat/load conditions. They had to run it *under load* in the tank to reproduce it.

Sent from my iPhone using Lake Ontario United mobile app

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  • 2 weeks later...

Well after a few months several mechanics no faults when hooked up to tester. It turns out it was a float inside the fuel modular was bad.

Guys at lime lake marina finnally found it. For some reason it wouldn't act up until it was in the water under load. Would not fault in tank.

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  • 4 years later...

I have a 2010 115 4 stroke with the same problem. However I get a 6 second beep and then the motor dies out. Want crank back up and run until a few hours of sitting. Does anyone else get the beep before motor shuts down with this problem?

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