2006 Mercury 115 EFI Stalling at Full-throttle

[EdK]

I have an intermittent but annoyingly recurrent problem with my 2006 Mercury 115-HP FOURSTROKE EFI motor that has escaped diagnosis and which no one can seem to fix.

This 2006 engine is from an apparently short lived-joint venture with Yamaha, and has less than 650 total hours.

Beginning about three years ago, the 2006 Mercury 115-HP FOURSTROKE EFI engine occasionally and quite suddenly would cut out when running at full throttle. Since then, and at least 50 times, the engine has suddenly lost power.

The sudden loss of power usually happens toward the end of the day angling, after five to six hours of making five to ten runs to new spots. The sudden loss of power has always occurred within the first 300 to 500-years of a run, and always at full throttle. And it is more likely to occur when the ambient air temperature is hot.

On some cool winter trips it does not occur for a week on the water.

When the 2006 Mercury 115-HP FOURSTROKE EFI engine stalls, I’ve found that if I immediately put it into neutral and go back and re-pump the primer bulb (which invariably is deflated and requires a lot of manual pumping to fully inflate), I can keep it running. At the time it also smells strongly of gasoline fumes.

After I get the primer bulb re-inflated, the 2006 Mercury 115-HP FOURSTROKE EFI engine generally runs well, but it can stall again on the next full throttle run when the air temperature is greater than about 75 degrees.

Only once did it actually stall out completely. At that time, I was unable to immediately restart it. I had it towed to a marina. There was no mechanic to be found and it started right up after about an hour and it ran fine.

Since the problem started, I have made sure to re-prime the primer bulb before every run. This strategy has successfully gotten me through the days on the water, but it has not been ideal.

One trip was reality hot, and the primer bulb kept getting soft, so I had to pump it up every 20 minutes, even between casts. The 2006 Mercury 115-HP FOURSTROKE EFI engine stalled twice even after re-inflating the primer-bulb immediately before the run, and sometimes it took 20 to 30 pumps to get the primer bulb firm. This prompted several conscientious attempts to get the problem fixed.

I've had the boat to the reputable mechanic that services the boat three times without resolution of the problem. Mechanics from two other shops took it on the water, but were unable to reproduce the stalling. I took it on the lake for several hours with an auxiliary gas tank but also was unable to stall the motor. Immediately after unhooking the auxiliary tank, it wouldn’t stall running it off the boat’s tank either.

Multiple new parts have been thrown at the problem.

• I’m on my fourth new primer bulb
• a new low-pressure fuel pump assembly
• a new anti-siphon valve
• a fuel pick up
• a kinked part of the fuel line removed
• a redundant part of the fuel line were removed
• the entire fuel line from the tank to the motor replaced
• all the fuel filters were replaced
• removed an in-line water separator
• the deck was taken up three times so that the fuel pickup, the anti-siphon valve and the tank could be re-inspected and they were found to be okay
• recently the Vapor Separator Tank was removed and inspected; a new needle, seat, high pressure pump and pressure regulator were installed
• the rectifier failed and was replaced-- but I think that this was probably unrelated.

The 2006 Mercury 115-HP FOURSTROKE EFI stalled out during my last trip in characteristic fashion. I called my current mechanic who came out for a ride and attached his diagnostic computer, but I was unable to stall the boat with him in attendance. He said that the starter and new rectifier seemed hot, and there might have been low air pressure. These were of unclear significance.

The problem is recurrent, but infrequent enough that it is difficult to reproduce on demand. When it occurs, I have to re-inflate the primer bulb to get the motor to run, and to take the boat to the shore to pick up the mechanic, and this make it unlikely to stall again in a time frame that the mechanic can afford to ride in the boat to diagnose the problem. So I have little hope of reproducing the problem under observation.
I use high quality regular gas with some ethanol, I've used Stabil with no apparent change.

Give me a suggestion [for the cause or the remedy]

I’m fairly sure [the problem is in] the engine and not in the fuel [system].

Q1: could this be some weird type of vapor lock?

Q2: is the motor overheating in some way?

Q3: is [the cause due to] some type of sensor failure?

Q4: why is the primer bulb always deflated when the motor stalls?

Q5: why is this getting more frequent?

Q6: why is [the occurrence of the problem] worse in hot weather?

Good mechanics and I [are both] at wit's end. I’ve spent about $3,500 on an engine that cost me $9,500 in 2007. Maybe it’s time to buy a new engine.

[jimh]

A sudden loss of engine operation with a distinct and immediate shut off is usually due to an electrical fault.

Electrical circuits can become intermittent when the temperature of the electrical assembly becomes too hot.

Check the circuit assembly that controls and generates the spark ignition.

Check for presence of spark using an in-line spark tester.

Check the engine cut-off safety lanyard switch.

The chronic problems with the lack of hardness in the fuel primer bulb could be due to the orientation of the primer bulb. For advice on primer bulb installation see

A Primer on Primers
https://continuouswave.com/whaler/reference/primer.html

[jimh]

Q3: is [the cause due to] some type of sensor failure?

Many years ago I was chasing a problem in my wife's car. It would sporadically refuse to start, usually while she was driving in short hops while shopping. By the time I would get there to rescue her, the engine would restart and run fine. After much time spent on replacing electrical components--which included finding that the engine had been running on only five of its six cylinders for some time--I took the car to my trusted mechanic. I told him not to do any diagnostic work, but to just replace the crankshaft position sensor (CPS). After replacement of the CPS the engine never exhibited the frustrating intermittent no-start condition again.

Some four-stroke-power-cycle outboard engines will have a CPS, or if the engine uses a permanent magnet alternator the CPS might be part of the alternator coil assembly.

In a similar manner, and again some years ago, I was chasing an intermittent condition in my six-cylinder outboard engine. There was a slight loss of power at full throttle, which was really only noticeable because I was monitoring the fuel economy. When the power loss occurred, the boat MPG would drop. The problem was found to be electrical and caused by one cylinder losing spark. After replacing that spark plugs, that spark wire, and that spark coil without a remedy to the problem, I concluded the problem must be in the spark generating assembly. That assembly was a $250 part (at that time, now probably twice as much), but my feeling was it was the last element in the chain of the spark generation that had not been replaced. After replacement of the spark generating assembly (in OMC lingo, the Power Pack) the engine ran flawlessly and never exhibited the problem again.

[Jefecinco]

Consider replacing the fuel tank vent hose. Virtually everything else has been replaced. Given the soft fuel squeeze bulb when the problem is encountered I suspect a fuel supply problem rather than an electrical one, however, I have no specific knowledge of your engine.

If the vent hose is original it may be old enough to have softened. When it gets hot it may sag enough to cause a minor restriction.

I would also add a strong dose of a fuel system cleaning agent to your fuel tank.

[dtmackey]

When the 2006 Mercury 115-HP FOURSTROKE EFI engine stalls, I’ve found that if I immediately put it into neutral and go back and re-pump the primer bulb (which invariably is deflated and requires a lot of manual pumping to fully inflate), I can keep it running. At the time it also smells strongly of gasoline fumes.

After I get the primer bulb re-inflated, the 2006 Mercury 115-HP FOURSTROKE EFI engine generally runs well, but it can stall again on the next full throttle run when the air temperature is greater than about 75 degrees.

This right here jumps out at me. The fact the primer bulb is going flat and after pumping gas back into the motor is a classic fuel delivery problem; that's where I'd focus.

Try running the boat on a small portable fuel tank to remove the boat's fuel system and see if the problem still happens. That is the first thing I'd have done in the problem-solving process rather than throwing parts at it.

Sounds like the mechanics like selling parts and not diagnosing the root cause.

D-

[jimh]

I am also concerned about the primer bulb, but usually a fuel related problem will not cause an immediate and sudden shut-off of the engine. The engine will stutter and slowly run out of fuel. For all cylinders to instantly stop working would be more indicative of an electrical problem.

If the engine sputters and bogs down and dies, that is certainly typical of a fuel delivery problem.

Also, how is the battery in this boat? Most Mercury engines with fuel injection will have trouble running if the battery voltage is not close to full-charge, and they definitely won't start without a good battery.

[dtmackey]

Most Mercury engines with fuel injection will have trouble running if the battery voltage is not close to full-charge, and they definitely won't start without a good battery.

A couple things to point out. While Jim is referring to a Mercury outboard, this engine is actually a Yamaha in Mercury paint and decals. If the battery is low, it would turn over slowly, but it it starts. The alternator would provide 14.5V to charge the battery and enough current (well in excess) to power the fuel pump-- but test the battery as that is the simplest of all things to rule out.

Second, start with the fuel and use a remote tank as I suggested. Fuel injection systems are far too complex to assume the lack of fuel would cause the engine to bog down and die. Depending on how sophisticated the system is, a lack of fuel supply would cause the engine to misfire and it's possible the ECU is shutting down the motor to prevent damage from leaning out and the misfiring. I've had this happen in cars.

If the primer bulb is going flat, you have an problem that needs to be resolved before chasing down other problems. Diagnosing a motor for problem A when problem B is apparent is a fool's errand as problem solving is a process, not a dartboard game.

D-

[EdK]

Thanks everyone for the help. The Mercury [mechanic] guy thinks [the cause of all these problems is] probably the fuel tank.

I will get an auxiliary tank. Once the engine stalls, I will connect the engine to the auxiliary fuel tank. I will see if that change prevents a relapse.

If [a different fuel tank causes the end of the problem], and if the [fuel tank vent hose is okay] then I will have to replace the fuel tank

Everything else [in the fuel system] has already been replace.

I cannot think that [the cause of the engine shutting off] is [due to] electrical [faults] as [the engine shuts off in] such a characteristic recurrent pattern.

About other suggestions, I don't know enough. I will bring them to the attention of the mechanic.

I will update this thread when I have more information.

[dtmackey]

I'll get an auxiliary tank....Everything else fuel-wise has already been replaced...

I'm very sorry that you've spent money with mechanics that didn't follow the logic steps in diagnosing the defect. You have many new parts installed that were never needed due to their lack of troubleshooting.

D-

[EdK]

Just got some interesting information: the Mercury 115 HP EFI has a Fuel Service Module (FSM) to lift the fuel to the engine, and this engine never should have had a primer bulb in the first place.

The claim is that the FSM gets fouled up eventually trying to pull gasoline through the primer bulb and can't do it.

Q7: Is this even possibly my problem?

Q8: Could my boat have been rigged up wrong since 2007, and this occasional stalling at full throttle be the only tell?

Q9: Can the FSM reliably overtake the primer resistance?

Q10: What do you think?

Sorry about my ranting.

[jimh]

In reply to Q7, 8, 9, 10:

All engines have a fuel lift pump that pulls fuel uphill from the fuel tank to the engine. For fuel to flow through a primer bulb only requires a slight pressure difference be created by the fuel lift pump. Fuel systems like this have been in use since the earliest days of outboard engines. As long as the fuel source is below the height of the engine's fuel metering device, the engine has to pull fuel uphill to get the fuel to the engine.

In conventional or classic two-stroke-power-cycle engines the force to lift the fuel is taken from a pressure check valve that taps into the crankcase. The pressure cycles operate an air-motor. The air-motor operates a fuel diaphragm pump. The pump pulls (sucks) the fuel uphill to the engine.

Generally in any fuel system, once the fuel has been pulled from the fuel tank to the engine, there is some sort of fuel reservoir. In a carburetor engine the fuel reservoir is in the carburetor bowls. In a fuel-injection engine the fuel reservoir is in the pressurized portion of the fuel-injection system.

In fuel injection systems there is a fuel distribution manifold that brings fuel to the injector or injectors. In a 2006 Mercury EFI engine, I am very sure there must be some sort of pump and regulator that maintains the fuel in the fuel distribution manifold at some elevated and constant pressure. The fuel service module (FSM) probably performs this function. Typically the fuel is circulated in the fuel manifold, and then returned to the FSM. There may be a cooler in the FSM to reduce the temperature of the fuel. Usually the FSM is also vented to the atmosphere, so any air in the fuel system is purged.

Again, if the primer bulb never gets hard, then my best inference is the primer bulb is improperly oriented. Again, read the article on primer bulbs and proper installation mentioned above and use the hyperlinked text to access the article.

HINT: the arrow indicating fuel flow direction should be oriented vertically and should point to the sky. If the flow direction arrow is oriented in any other manner, the primer bulb will probably never get firm with pumping.

The quality of the primer bulb is also a factor. Only use OEM primer bulbs.

If the engine manufacturer recommends not having a primer bulb at all, then remove the primer bulb. Retest without the primer bulb. That should be an easy test to make.

[jimh]

Regarding the fuel tank and how it could affect the fuel flow to the engine:

In some boats the manufacturer will have installed a check-valve at the fuel tank pick-up fitting. The check-valve is designed to prevent the flow of fuel back into the tank from the fuel lines.

A check-valve fitting on the fuel tank could be restricting fuel flow.

ASIDE: in this discussion I do not see any mention of the boat that is involved. Please mention the boat maker, year, and model.

[dtmackey]

A check-valve fitting on the fuel tank could be restricting fuel flow.

I beleive you are referring to the anti-siphon valve. I've seen a nunber of them go bad over the years. Stay away from the aluminum ones as many use a steel spring and ball that can rust if your fuel picks up water, which is very possible since this valve is before your fuel-water separator. Try to find the brass units as the better ones use a stainless steel ball in the valve,

This valve is also mandated by the Coast Guard for installed fuel tanks below deck and the purpose of this valve is to prevent fuel from being siphoned into the bilge in the event of fuel line failure. The fact that fuel also won't drain back into the tank is an added benefit, but not the reason this valve is installed.

Information regarding the legal requirement. https://www.law.cornell.edu/cfr/text/33/183.568

D-

[EdK]

Thanks again for the answers.

I've had 4 primer bulbs, oriented essentially horizontally (maybe a little upward toward the engine) on the back of the boat, which is a 2006 Crestiner Canadian 1850. I've had the anti-siphon valve checked 3 different times and the mechanics have been reluctant to just remove it.

I plan to remove the primer bulb next time I take the boat out for a run, but it feels a lot like going to sea and purposely leaving my lifejackets home, as I have primed the bulb to a hard state before almost every run at full throttle for 3 years.

As I understand it the Fuel Supply Module of the Mercury 115 HP EFI engine is in and part of the Vapor Separator Tank, which was fully serviced, with replacements of parts this month.

[dtmackey]

I've had the anti-siphon valve checked 3 different times and the mechanics have been reluctant to just remove it.

I'm not surprised they have been reluctant to remove it, it's a federally mandated item in the boat, so the liability on them is huge if something were to happen. They are inexpensive and easy to replace and with the number of parts they've thrown at the motor, I'm curious why they didn't replace.

D-

[jimh]

ASIDE: The method by which a siphon works is an intriguing sidebar topic. See

https://en.wikipedia.org/wiki/Siphon

[GoldenDaze]

A friend of mine had a very similar-sounding problem with same engine on his 190 Nantucket. In his case it had nothing to do with the engine: there was plastic or other debris in the fuel tank that would occasionally slosh over to the fuel pickup.

[EdK]

I have an update with my Mercury 115EFI.

October 2022

I took out the boat for diagnostic runs. [The Mercury 115 EFI engine] stalled out at full throttle [when running from] the boat’s fuel tank. The engine then twice thereafter stalled the same manner using an auxiliary fuel tank.

The Mercury support fellow said that the engine wasn’t supposed to run with a primer bulb [in the fuel hose from the fuel tank] so I removed [the primer bulb].

I ran the the engine for [enough] time to assure that the fuel lines were full, and then the engine stalled out in typical fashion at full throttle.

After stalling with an auxiliary tank, I’m certain that the problem is in the engine, and not in the fuel tanks.

Q1: Is the motor overheating in some way?

Q2 Is [the cause of the engine stalling be due to] a sensor failure?

Q3: Could [the cause of the engine stalling be due to] an electric fault precipitated by the electric assembly that’s too hot running at full throttle?

Q4: Why is the primer bulb always deflated when the motor stalls?

Q5: Why is [the engine stalling] getting more frequent?

Q6: why is [frequency of the engine stalling] worse in hot weather?

Again, I could use some help. Thanks in advance.

[Phil T]

I re-read this entire thread.

I still think the stalling is fuel starvation.

Why is there an anti-syphon on the fuel line?

You need to inspect the VENT side of the equation.

Please take photos of the tank, fuel line going to the engine so I can see the entire line.

Does the engine stall at less than full throttle? If so, what is the highest speed you can go?

Confirm this engine is CARB'ED or EFI

What model of boat is the engine installed on?

Be happy to review this via voice or vidchat call. Email is in my profile.

[GoldenDaze]

I can certainly understand your frustration! You've tried a lot of things and gotten basically nowhere. But I agree with Phil, it's hard to imagine how this can be anything other than a fuel delivery problem upstream of the primer bulb. While there are lots of electrical problems that could cause an engine to stall at high speed, there are none that will deflate the primer bulb. Ditto basically any other possible problem on the engine itself.

What components are both:
1) between the atmosphere and the main fuel tank and the primer bulb; and
2) between the atmosphere and the auxiliary fuel tank and the primer bulb

I'm guessing there's a common length of fuel line and maybe a connector, though your original post does sound like you've replaced most everything. But it seems like that MUST be where your problem is.

Jefecinco's suggestion to check the vent line was a good one, though your experience with the auxiliary tank would seem to rule that out. It would similarly seem to rule out problems with the tank pickup or and below-deck fuel filter. There's been much discussion here about delamination of glossy gray fuel lines and that could be an excellent possibility.

It sounds like your main fuel tank is built-in, and while you didn't mention what model your boat is, given the year and the engine I'm guessing it's a 160 Dauntless or a 190 Nantucket/Outrage. I don't recall any other boat offered with that engine in the 2006 timeframe, with the 160 Ventura out of production by then and the 180 Dauntless having a minimum of 135hp. I have a 2003 160 Dauntless with the same engine (also 2003) and while I'm no master mechanic compared with some others here on CW, I do know my way around this boat and motor. I also have a primer bulb and it's never been a problem as long as I replace it annually (with a Mercury part not a cheap aftermarket).

By the way, you have been unusually thorough in giving us information to work with! That does make it surprising and annoying that it hasn't been figured out yet.

-Bob