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2005 merc 115 4 stroke help

Old 10-20-2014, 08:36 PM
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Default 2005 merc 115 4 stroke help

Boat will lose power during WOT occasionally. There doesn't seem to be any kind of pattern, nor can I recreate the problem on demand (or any certain action ie: throttle up/down, shifting, etc.)

Had 300 hour service done with all filters, replaced fuel sending unit (It was badly corroded) and thought that was causing air to enter tank/fuel lines causing motor to shut off. (idk, shot in the dark)

took it out last weekend and motor again shut off several times (the most ever in one time).

The catch is... my onboard charger was faulty so batteries couldn't charge during the day. COULD... the batteries be so drained from trim tabs, electronics, etc. that motor's fuel pump couldn't supply the gas? there for motor shuts off?

During the day chart plotter shut off a few times from dead batteries and TM was dead.

When motor shuts off, I can go to the in line hand primer and prime the lines (It will be completely limp).

I've done some research, and it looks like motor has a low and high pressure fuel pump, one possibly may be faulty?

Thanks in advance guys
Old 10-21-2014, 02:26 AM
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The first thing I would do is replace the battery with a new one. These newer motors do not like low voltage and it can cause the problems you are having. Also the internal filters on my Yamaha 115 were all clogged up with a residue that is left behind by E10 fuel. My tech cleaned the VST filter and the injector screens and that solved my WOT issues. I do not use E10 fuel anymore in the boat.
Old 10-21-2014, 04:42 AM
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Start with what Fireman said. Fix the known problems first. Low battery voltage can cause problems throughout the electrical system. Are you saying the boat completely shuts off and you have to restart it or it looses power? I have had a similar issue, but it never shuts off.
Old 10-21-2014, 06:15 AM
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Thanks fireman, I'll look into that first.

Mo, the majority of the time is shuts off completely, sometimes it's like it will catch enough fuel and turn back on with out having to crank. If not, I can go back and pump the ball, and motor will turn over and run like a charm.
Old 10-21-2014, 08:50 AM
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You could also just disconnect the accessory batteries to eliminate them from the system. Check the battery connections for the engine battery. Make sure they're tight and clean. But, sounds like a fuel issue. Mine would start bucking real bad from 2k rpm and up. But, the condition was very intermittent. I removed the fuel filter at the left rear of the block and found what looked like brown crystal chunks. I did some online research and found where someone else had the same condition and turns out it was the fuel line breaking down from the inside. Seemed to be from ethanol. I keep checking the filter and have not seen any more debris. I have also read in the owners manual where ethanol can cause a vapor lock condition. Do you have an external fuel water separator? If so, I would start filling with rec 90 and when you know you have all the e-10 fuel out change/clean all filters and run it some more. If you don't have an external water separator I would install one. Problem persists I would start looking at fuel pump(s).
Old 10-21-2014, 05:40 PM
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I do have an external one, I checked batteries today. All are in good shape and pretty new 2013. Connection was good, but I'll check output tomorrow. I'm also running it tomorrow after work until dark. I've done some more research and many people are telling me the ethanol gas is really that bad. I thought since I just did the service a month ago I'd be good, but they say if the lines are bad it doesn't matter nor does it take long.

Will keep you posted.
Old 10-22-2014, 07:17 PM
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checked the batteries today, under a load it only dropped to 11.86.

took it for a test drive after work... 36 miles with constant shut off, start, shift, etc....

couldn't get it to shut down on me like it was doing... This is after fixing the wiring on the on board charger. A pretty savvy mechanic friend of mine says the fuel line leaving the primer ball is toast, he said he can feel it doubled sided where the ethanol ate it up. I don't quite think that... at least for now anyways.

on another note, a bad one. I'm starting to hear a slight rattle sound when you shift into gear... its not constant, but it is consistent when you can get the noise started. other times you shift, you may not hear it. Its hard to tell, but I don't think it gets any louder or worst as I accelerate or run WOT...

any ideas? thanks
Old 11-04-2014, 06:11 PM
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So another update guys...


I've decided to go ahead and replace the fuel pump(s)...

I called one mechanic and he qouted me $700 for non OME parts to replace both.

From talking to him, there is two fuel pumps, a low and high pressure side. One I guess pumps from tank up to motor, then another that actually pumps into the motor.

From looking at this schematic, and looking at my motor... I can only find the one smaller one.

Name:  merc fuel pump presentation.pptx.jpg
Views: 203
Size:  99.8 KB


Any help appreciated!
Old 11-04-2014, 07:47 PM
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Is the fuel line grey? If it is I'd listen to your buddy and replace it. Once you've eliminated the fuel line I'd have someone diagnos the problem before throwing $700 at not knowing if that's the issue.
Old 11-04-2014, 07:51 PM
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Sorry guys for jumping to posting first without doing more research.

I've found both the mechanical fuel pump which is easy access and looks to only have one diaphragm that could be replaced. It also has a filter below it which was just replaced at 300 hour service.

The second fuel pump is the "Fuel injection pump" located behind the intake assembly. Its a little harder to get to and requires removing the fuel/water rail, fuel injectors, and the intake assembly. It has one filter underneath it which I will check along with replace the motorized pump.

I'm not the most savey or mechanically inclined when it comes to outboards...

Is there anything I should be concerned with when attempting this part exchange?

Also, Is there a way to test the motorized fuel pump before ordering a new one? It's roughly $250 alone...

Thanks again guys!
Old 11-04-2014, 07:56 PM
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Originally Posted by bms1939 View Post
Is the fuel line grey? If it is I'd listen to your buddy and replace it. Once you've eliminated the fuel line I'd have someone diagnos the problem before throwing $700 at not knowing if that's the issue.
BMS, The line is grey...?

I've disconnected it from the intake side where it meets the primer bulb and looked inside. From what I can tell, there is no separation I can see... Due to my symptoms, I don't believe its the fuel line. I think the motor would be breaking up more severely then what it is doing now. Right now it runs like a champ from idle to WOT. But on random occasions, it will just lose prime/gas and choke out and die.

I hope there isn't a air leak somewhere, hopefully just a fuel pump problem.

None the less, when and if I get this fuel problem fixed. I will be replacing all fuel lines along with primer bulb.

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