[bluechevyy]

Please anyone that can help! I have a 2005 Mercury 4 stroke optimax (which I am told the power head is a Yamaha). 200hrs on the engine is all.

I am experiencing a major power loss at full throttle. One day it ran great, the next it runs at ~3000rpms max throttle. You can feel it stutter as it's accelerating to the 3000rpms. Also, it starts awesome and ides pretty good. You can feel a little more vibration than you use to at idle.

Here is what I have done so far. I have replace the spark plugs, check the oil level etc. Made sure all electrical connections are plugged in all the way in the engine. I checked spark with an inline checker and also at the output of the plug and all looked good to me. I changed out water separator filter and internal filter. Found nothing. Gas is not old or water contaminated. Also I took it out and separated my fuel system all together by hooking up an external tank and the problem was exactly the same.

Here's where the frustration comes in. I took it in to a local marine dealer and they put it on their so called diagnostics tool and it told them the crank shaft position sensor was bad. So, 3 and a half weeks later I get the boat back with a bill for just short of $700. Still does the same thing. I took it to another marine dealer and they did "extensive diagnostics" and determined it was the #2 & 3 ignition coal. They replaced the part and a week later and $590 later it still does the same thing. I'm into a fix almost $1300 and I have no faith that they know what's wrong. Please help.

Now it's back to the 2nd marine dealer for the total of the 3rd visist and they pulled the injectors to clean the screens. Of course they don't have the orings to put them back! Another week of waiting parts. The guy said he wasn't convinced the injectors were the problem either. HELP HELP please. I truely love my boat and going out on it on a regular basis,but, I'm starting to think I stepped in to deep on this one. Who would expect a motor only 4 yrs old to have this costly of problems. I don't neglect maintinance on it either. I run fuel saver change oil regularily etc.

I'm trying to get my 5, 3, and 2 yr old girls out to fish before winter sets in.

Thanks in advance for any ideas!!!!

Curt (out of Portland, OR)

[Faztbullet]

To get the best answer lets get a better idea of what you have.. a Optimax 115 is a 3 cylinder 2 stroke DFI engine made by Mercury and the older 115 4 cylinder EFI was a 4 stroke made by Yamaha...so is it a 3 or 4 cylinder? Are you checking oil in oil tank or in crankcase? I am thinking you have a EFI since you said you changed oil.

[sdsaw]

Well, if you do have a 115hp fourstroke, there was no mention of a VST(vapor separating tank) service.
Do a search over on the Yamaha/Suzuki section for "VST Cleaning" and you will find many posts referring to this common problem with the EFI motors

Here's one of the posts:
http://forums.iboats.com/showthread....t=VST+cleaning

Also, check the thermostat

Good luck!

[bluechevyy]

I have the 4stroke made by Yamaha. It is a 4 cylendar engine.

[Faztbullet]

I went back over your posting and you stated they changed 2 & 3 coil, this is confusing as engine has only 2 coils, and top fires 1 & 3 and 2 & 4 at same time. I have seen only 3 problems on these engines: (A).. injectors (B).. harness where it plugs into ECM (C)..oil pressure switch. Changing the screens in injectors really does nothing but remove any debris in filter, they(injectors) must be flowed ,cleaned and balanced. I suggest you send them to Tony/Linda @ Brucato (Brucatosvs.com) as they will do all the above for about the price of 1 replacment injector. The harness probem is simple as harness unplugs itself at top, engine will run,show no code troubles, and miss like it has plugs fouling in the 3000 rpm range. The oil switch is a simple check, just unplug it and run it , if problem goes away replace it. Is your oil/hot horn working? Another thing it could be is the temp switchas if bad it will retard timing but this wont cause a stutter/miss just lack of power.

[blackbox]

faztbullet gave soom great info. sorry for your motor problems. sounds like fuel system issues. hope the repair shop gets you going!
yamaha recomends a 10 micron pre-filter. if you donot have one, it may be a good time to have one installed. a good filter may prevent other fuel problems.

[bluechevyy]

The motor does have an internal fuel filter in addition to the water separating filter (external). Currently I am waiting for the shop. They currently have pulled the injectors and are flushing them, but, waiting for o-rings kits before replacing them. Said they would be in by late this week. Then they are going to have me come down and water test it with me present.

Thanks for all the input so far from everyone!! I am going to follow up on the harness to ECM and checking the oil pressure switch if the fuel injector cleaning doesn't help.

I will keep you posted on the outcome!! It's killing me, I'm a die hard fisherman and I've been without my 20' Northriver in action for over a month now!!!!

Curt

[BW3D]

I had the same problem with my Merc. 40hp 4-stroke....Turned out that it was an electricla problem....Cant remember the mane of the part replace but it charges the battery. Turned out that it wasnt charging the battery and in turn the fuel injectors and spark plugs werent getting enough power at higher RPM's. I will try to rmember the name of the part and post it for you.

[bill and doris]

When my 115 Merc 4 stroke acting like yours I chased everything. After 2 years the fuel pump finally quit completely. The folks here were able to direct me where to get the parts breakdown on the motor and what the part's actual part number was. Took about an hour to get manafold off and home. Fuel pump is hidden behind manifold. Pulled pump and replaced. Had everything reinstalled back on motor in about an hour. Runs perfect now.

[bluechevyy]

Well after all the time and $$$$ ($1200), the problem was what I thought it was in the beginning, just needed the injectors cleaned. What a waste. There should be some sort of recourse on these marine stores that are wasting your money on parts that are perfectly good. Well I will for sure pass along to ALL my boat friends not to do business with the company I first dealt with.

Thanks everyone for your great feedback and help. It gave me lots of ideas and things to look at.

I'll chalk it up to a bad experience!!

Bottom line is I'm back on the water and lovin' it!!!

Thanks,

Curt