07 Mercury 115 Optimax Warning System Diagnosis

[frozenokie]

Bought a 2007 Tahoe 195 OB boat with an 07 115 Optimax and it came with a problem or probems.

First, I took it to the lake and found that the RPMs went upwards to 7000!!! YIKES!!! I get home and find that the prop hub was slipping. During the time on the lake, I didn't a warning until I was way across the lake. First started as a 4 beep every two minutes, then it limited my RPM to around 3000, then it gave me a continuous beep followed by a 4 beep warning and limited me to idle.

I take her home to start diagnosing. My first step was draining the fuel bowl/filter to check for water in the fuel - which there was no indication of water. With water supplied, I start it and wait........I get no warning horn until I start to give a little throttle, then it immediately sounds a continuous warning horn, then goes right into a 4 beep warning every two minutes a couple different times, then it goes away until I throttle it again.

Oil tank full, noticeably burning oil, just installed brand new impeller so water is nice and cool and lots of pressure coming out of the water jet. No issues starting or running while in idle.

Going to ground the oil switch circuit tonight to observe if the beeping goes away since I've had two licensed mechanics advise that since they are finding many problems with the oil switch or sensor.

Can someone point me in the right direction as far as possible faulty sensors or problems??

 

[Chris1956]

OK, 4 beeps every 2 minutes is low oil, or water in fuel. Behind the vapor separator is a .custom Merc water separator, with a water sensor. I would recommend you dump it out or replace it ($25). You will need a rubber strap wrench to get at it.

Continuous beep is overheat or overspeed(over 5800 in gear). Although I didn't see it, limiting RPM can be done by low oil or likely overheat.

See page 177 in this manual. www.boatinfo.no/lib/mercury/manuals/115-135-150-175_optimax.html#/176

 

[frozenokie]

Thanks Chris... I have read the possible warning horn and light signals chart from the manual also.

To clarify, I was getting the continuous beep without even reaching 2000 RPM while on the trailer trying to diagnose the horn signals, so this condition was the hardest for me to figure out which area to start diagnosing. I was on the lake with it the first time when I noticed the RPM overrev to 6500?, but I could not tell if the limiter was working...thank goodness I was watching!!!

The first thing I did was drain the water/fuel seperator and was going to ground the low oil sensor to see if the oil sensor is bad (which is what the dealers and mechanics are finding at local shops here). There was no trace of water from either drain spigot on the seperator.

Did you mean replace the water sensor or the red "castle topped" filter and insert?

If that beep doesn't go away with the oil sensor grounded, then I know it has to be either a water in fuel issue (and I have missed draining it all out) or I might have a bad water detection sensor. My last suspicion would be water temp sensor(s).

I also agree that even though the manual doesn't state it, a low oil condition has limited me before on other engines.

So I will address the oil sensor first and report back with my findings...

 

[Chris1956]

I suspect (no proof), that the motor will give an overspeed alarm, if you rev it in neutral. Overspeed alarm is continuous beep.

There is a drain on the vapor separator, on the front of the motor. Did you drain that? Water left in the fuel line plays havoc with the two elec fuel pumps.

 

[frozenokie]

I suspect (no proof), that the motor will give an overspeed alarm, if you rev it in neutral. Overspeed alarm is continuous beep.

That was my exact thinking too...not for sure if it does or doesn't sound on that condition.

On draining the seperator...Yes, I did that before I did any other repairs. I also drained the back side of the same seperator bowl. I used a glass jar to drain into and found zero water...but I should probably do that again to be for sure.

I'm choosing Saturday morning to pull the oil tank in order to bypass or jump the oil switch wires together to see if the oil switch (sensor) is bad. With some research, and asking a local mechanic for assistance, I gather that the sensors on the Optimax engines are suspect to fail prematurely, escpecially the oil switch or sensor.

I'll let ya know what I find...

 

[frozenokie]

I disconnected the low oil switch and grounded the two wires together and both the continuous and the 4-beep alarms went away. While at the lake, after about 5 gallons of fuel through it, it started spitting, chugging, and what was weird was it started loping. Almost like a fouled plug or water in the fuel, etc. Mysteriously went away as I was putting her back on the trailer...


I'm scratching my head on this one, but I think it might be my MAP sensor?? Any thoughts??

 

[Chris1956]

Sorry, I have no thoughts.

The last fuel injection system I really understood was on my 1980 Datsun. They have become significantly more complex since then. I am not sure why, as that car got real good gas mileage and had good power, and lasted.

I would check for water in the fuel, just to rule it out. The local mechanic says replace plugs every 100 hours. They are quite expensive, but maybe worth it, if you have not done it. They are a real PIA to change.

 

[frozenokie]

LOL on the Datsun lasting longer than modern technology :-D

Yes, I replaced the plugs before I ever started the motor. Being seasoned with 2 strokes has taught me that much PIA to change?? I had no problems unless there's something I'm missing?? If I am missing something, then maybe it's the cause of my current problem...??

The only other things that are mentioned in the manual are fuel injector faulty, or an ignition coil is going bad...which I've only experienced a faulty coil on an Evinrude FICHT 175, which gave similar symptoms but it did not lope or surge like this Mercury...

Looks like I'm gonna have to turn the ball cap backwards and dig in!!

 

[frozenokie]

Decided to try the Stabil Fuel conditioner since there was old fuel in the tank when I bought it. Then I'll take to the lake again and see if it acts up again.

If she's gonna act up, I want it to be consistent so I can pinpoint the problem.

 

[frozenokie]

Very interesting results...I had no problems with the motor last outing It appears, at least at this point, that the fuel was just old and needed some replenishing. This gives me hopes that when the old fuel is ALL gone, she'll be running much better.

I did, however, observe another problem...the REV limiter doesn't seem to work. I had it go over a couple times slightly and realized that the REV limiter isn't working.

How do I test it?