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2008 Mercury Optimax 115 hp, loss of power

oceanhunter

New member
Hi my meercury optimax 115 hp is playing up. The problem started gradually over 4 fishing trips. First time after going at around 45km drop back to troll for a while went to go back to 45km but would not go past 2700rpm with throtal fully on top speed now around 15km. I stop motor anchored and fished for 2 hours. Start up motor after fishing runs good back to 50km plus go home no problems. The next trip the same but this time on the way home engine speed at full revs is around 30km. I go home thinking motor starving for fuel, so I change fuel filters inline tank filter and onboard fuel filter, air filter, change all fuel lines to fuel tank. I check breather in fuel tank working etc.
I go out on water go full throtel around 50km plus but after 10min slowely drops back to 15km 2700rpm full throtel. The motor is out of extended warrenty by one month. Currently motor is in at Mercury Dealer/Mechanic and he has had it in the water twice after timing, checking motor with laptop and put kit through fuel pump. Still the problem is there. The mechanic says he has done all checks with computer checked fuel presure, checked each spark plug etc. The top spark plug seemed bit wet which he says indicates too much fuel if anything.

Last trip my misus said I smelt oilly. The motor its self seems to be using a little more 2 stroke oil. The mechanic said the motor starts and idols perfect just won't go past around 2500 rpm??? When your on the boat to any novice it sound like its starving for fuel. Is there anything electrical that can cause problem??? Any suggestions would be appriciated.
cheers

Lionel
 
These motors are pretty complex with many sensors etc.

If the tech is certain that both your fuel pumps are working properly (low pressure, crankcase pressure driven and high pressure, electric) then the next leading culprits could be:

The VST (vapour separtor tank) could be restricting fuel to the rails, or,

The fuel injectors (that feed the rails) could be acting up (one or more of them could be clogged), or

You could have a bad tracker valve allowing fuel to escape into the air system, or

One or more of the direct injectors could be clogged/not working properly.

The Oil doesn't mix with the gas until it gets into the cylinder. The oil is mixed with air and is then sucked through the reeds (as in a "normal" 2 stroke) and then into the cylinder through the intake port. When the piston has traveled enough to seal off both the intake and exhaust ports the direct injector "squirts" the gas into the air/oil mixture in the cylinder and then the sparkplug fires it.

For the gas to get to the cylinder it comes from your tank, via the fuel line to low pressure fuel pump (through whatever filters you have in line). From there it travels to the high pressure pump, through the vapour separator and up to the fuel injectors that feed the fuel rail (the ECM tells which injector to push fuel into the rail). There is a parallel "air rail" that contains air pressurized by a compressor. The two rails are separated by a tracker valve. When a particular cylinder "needs fuel" the direct injector opens and the compressed air from the air rail pushes the fuel from the fuel rail through the injector into the cylinder.

Excess fuel at the rails (which is now highly pressurized) goes through a fuel cooler and is returned to the vapour separator/high pressure fuel pump.

So, as you can see, there are numerous points of failure between the fuel line and the actual cylinder.

Even if a particular cylinder is not getting gas (or not getting enough because of a partially clogged direct injector, or anything upstream from that), the air and the oil still gets to the cylinder which would cause the oil to continue to burn and the oily smell (since it may be burning at 10:1 or something like that compared to the normal 100:1 which would be normal).

I find it unusual that nothing would show up on a computer scan - the diagnostic system on these is pretty good and should pick-up the issue, but since it isn't and your current "tech" can't find the issue I would look for a different Merc certified mechanic who is also certified, and has experience, working on Opti's - they really are a different kind of beast...
 
I am having the same issue with my 2008 115 Optimax.
It happened six years ago, and I had a bad coil.
My problem seemed to occur after a long run, when the motor got warm.
The factory authorized Mercury mechanic I used for service said there was no way to test the three coils because the problem was intermittent, since it seemed to happen after I'd run a while in hot weather.
I bought a coil, and replace the bottom one, because it was the hardest to reach, and I made a test run to see if that was the problem. It was.
I have just begun experiencing the problem again, so I am replacing the other two coils.
I'll save the old coils, just in case it is the bottom one again.
When my motor gets hot, the Smart System goes into Guardian mode, to protect it. I can't get above 2700 rpms, and it runs rich and uses lots of oil. It resets itself once the motor cools again. I have that problem when weed get onto my cavitation plate. I find that not running on plane when I'm going through weeds keeps that from happening. I guess the having more hull in the water pushes the weeds out of the way.
 
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I have the same problem on my 2010 115 Optimax. Any resolution on this?

My motor's problem was a bad coil. The motor has three coils, one for each cylinder. Since the mechanic said there was no way to test the coils to see which one was bad, I bought one, and replaced the lowest coil, which was the hardest to reach. Then I took the boat for a test drive, prepared to return to the dock and move the new coil up until I found the bad coil. Fortunately for me, that was the bad coil, and it ran great. Problem solved. Several years later, I had the same problem again, so I replaced both of the remaining coils, and it's been fine for three years. Knock on wood!
My factory authorized mechanic told me, belatedly, that this particular motor was known to have issues with coils.
 
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