Yamaha F115 Hiccups at high RPM

[NCSkeeter]

My 2007 Yamaha F115 has developed a problem running at high RPMs. After I have been running at around 5500 RPMs or higher, the RPMs quickly drop to 4500, and then the boat takes off like a scalded cat. The problem is intermittent. I can run several miles without it happening.

I checked the 10 micron water separator and the gas looked good. There was no water and maybe 5 particles of some kind of sediment. I replaced it anyways. It has a full tank of fresh gas. I used the boat all summer without issues. I always use Marine Stabil for E10.

I pulled the spark plugs and they look good. I also checked battery connections. The fuel bulb is staying hard.

I'm still in the Yamaha Extended Warranty. I took it to the nearest Yamaha service center which happens to be a Cabela's. They see the sudden RPM drop in the ECM history when they hook it up to the computer. There are no error codes. At the same time they see a drop in battery voltage to 10.6V. They also see the throttle postion sensor doing something, but that may be when I backed off the throttle when the problem occurred. They are stumped and called in a Yamaha field service rep. He's contending its a fuel issue.

I don't believe its a fuel issue because the boat has been in use, the behavior comes and goes so quickly, and a severe voltage drop observed in the ECM. I think it is definitely electrical. The service manager at Cabela's agrees and is bringing in a dyno load from home to run it under load at the shop tomorrow.

Has anybody see an F115 with this behavior?

[boats.net]

The most common reason for rpm loss is fuel related problem, fuel restriction, loss of pressure or injectors. If the voltage drops to below 10 volts the ECU will shut down but not normally causing a miss but it does need to be checked out why it is dropping.

[TownsendsFJR1300]

My F150, when I was using car fuel with ethonol, caused the plastic fuel filter at the front of the motor to expand/turn yellow (it has an o-ring atop it) and not fully seat causing an air leak... Check that pastic filter case and make sure its fully seating...

Also, I suspect yours is the same, there should be a clear drain hose on the starboard side of the engine attached to the bottom of what appears to be a carb. There is a phillips head screw there that allows draining of this bowl. I have had small particles get past the main fuel filter (and a transom mounted filter) and get into the FI pump area.

The fuel pump resides in there and has a filter. Loosen the screw and catch what comes with a very, very clean container (I use a clean tuna fish can). Look for particles coming out. I also gently blow back into the hose and then give the primer bulb a squeeze to flush any crap out of there. If that filter is borderline clogged it'll cause problems.

BTW, I stopped using ethonol fuel and use marina , non-ethonol fuel (more $) but the engine runs considerably better with the higher octane and no ethonol...

Good luck...

[NCSkeeter]

The ECM is reporting a battery voltage drop from 14.6 volts to 10 volts when the RPMs suddenly drop. I don't see how a fuel flow issue could result in low system voltage.

Also, it is a very rapid RPM loss and it recovers very quickly. It feels like someone turned the key off for a split second and then immediately turned it back on.

[TownsendsFJR1300]

Can you monitor the voltage while under way?

The battery, at its lowest voltage shouldn't go below 12 volts. Charging, while under way in the 13's. If you get a sudden voltage drop to 10 volts, sounds like the battery itself has a dead short inside (or a bad connection/bad ground-you'd generally loose ALL voltage).

Voltage drops, there's not enough voltage to run the fuel injection/ignition etc, engine dies.

Check battery connections/ load test the battery or try another battery while watching the voltage underway. I suspect when the boat is underway, bouncing, its shocking the connections inside the battery causing the short...

Good luck..

[NCSkeeter]

I could bring a DMM on the boat with me to monitor voltage. From the ECM diagnostics, we can see the the voltage at the motor only drops for a very a short period of time. I doubt I would even see it on a DMM. We've verified the charging system is charging at around 14.5V.

Since the battery can start the motor just fine, I'm thinking the battery itself is ok. My guess is that I have an intermittent relay or connection or that something is causing excessive current draw, bringing the voltage down. I'm thinking that its likely ignition related if its excessive current, due to how large the current would have to be to cause that kind of voltage drop.

Cabela's checked the ignition coils and spark plug wires. I have replaced the spark plugs in a cheap attempt to rule them out as the cause.

I will report back once I can get out on the lake. It was too rainy here today to get out.

[TownsendsFJR1300]

F115

A dead short in the battery can come and go. Any automotive store/Walmart will check the battery for you for free.

IMHO, I would check the basic's first. The engine can put out 14 volts all day but if the battery shorts out internally, it won't make a difference, you literally have no battery to store that power/run the engine....

[NCSkeeter]

I think I found my problem. I looked closer at the wiring in the bilge and found an inline fuse holder that is extremely corroded. If looked good until I pulled the cover off, then white powder came pouring out.

I am assuming that it must be the problem. After looking at the amount of corrosion, it is amazing that the motor ran as well as it did.

[TownsendsFJR1300]

F115

If thats one of the main harnesses to the engine (and not the bilge pump), that would definitly cause your low votage drop/problem.

After cleaning it up/replacing it, I'd put a bunch of di-lectric grease in there to keep further water/corrosion out...

Congrates!

[NCSkeeter]

It definitely isn't the circuit that powers bilge pumps, lights, and other accessories. All of that is on a much larger gauge wire that I can trace to the dash. The fuse in question is on a single smaller gauge wire (16awg or 18awg?) that goes into a big wire bundle in the bilge. It's hard to trace where it goes after that. I can't believe that a boat that I bought new has wiring that is such a mess. It also explains why I never saw a voltage drop at the dash, since everything up there is powered off a different breaker.

I don't have an electrical schematic for the motor. In addition to the heavy cables for the starter that go to the motor, does 12V go directly from the battery to the motor? I don't have any battery switches.

Thanks for the help! I probably wouldn't have found this if I hadn't pulled the battery to check it closer. The battery terminals looked so clean that I had ruled out corrosion in that area as my problem. This fuse holder looked brand-new from the outside, so I assumed it was fine.

[TownsendsFJR1300]

F 115

You should have 12 volts to the engine either after the battery switch (which you don't have) or direct from the battery to the harness/engine.

The starter gets 12 volts usually after going thru a relay. I suspect thats probably fused as well.. That smaller wire may be the trigger wire for the starter relay to activate the starter or even the ignition. In either case it needs to be addressed. It might be worth your while to untape the mess just to fix their mess they made so YOU KNOW everythings correct and doesn't get you stranded....

BTW, on my 1997, 21' Angler CC, all engine cables of course run thru the hull but not in the bilge pump area (where salt waters going to be) and pretty much way above where there's water.

When they re-rigged my boat with the F150, I spent a FULL day re-routing/taping/wire tieing, etc cleaning up their mess... Extremely sloppy! The trim (steeering) tab was set opposite it was supposed to be (per the Yamaha manaual) and the wrong prop installed(max 4800 RPM, tops!!!) Some people don't care about their crastmanship or lack of, just get it done ASAP...



Good luck..

[TownsendsFJR1300]

F115

I doubt its the wire for the starter as you don't have any problems cranking...

If its a main line for the ignition that makes sense looseing 12 volts and then back up again as your corrosion allows somewhat of a connection..

If you have a test light, it should activate when the key is turned on(don't crank it dry). If you don't have test light, you can rig something with a 12 volt bulb and 2 wires using them as your connectors/probe... With 12 volts, the bulb should be good and bright..

[THerbert]

Check battery cable ground at the motor. My F150 stoped dead in the water. Took me about a 1/2 hour before I found the Battary Cable to the motor was loose at the motor.

[NCSkeeter]

Last night I determined that the wire in question is not part of the ignition circuit. I removed the fuse. With the fuse removed, I hear the fuel pump run when i turn the ignition to run. In fact, I can't find anything that doesn't work with this fuse removed (without actually running the engine).

I am definitely going to have to open up the bundle to determine where the mystery wire goes.

[TownsendsFJR1300]

F115

Were you able to put a test light or bulb on it and see when it activates (with or without the key on)? I don't know for certain but I doubt the fuel pump runs on the same line for the ignition... Just curious...