Mercury 2005 115-HP FOURSTROKE Problem

[MisChief15]

Recently I bought a used 1998 Outrage 17 II powered by a 2005 Mercury 115 FOURSTROKE (with a Yamaha power head) said to have 260-hours run time. On my first use of the boat, the engine ran roughly and seemed to lose power.


SUMMARY
The poor engine running with a 2005 Mercury 115-HP FOURSTROKE was due to fuel starvation caused by obstruction of fuel flow at an in-line filter under the cowling.


THE PROBLEM AND ATTEMPTED REMEDIES BY MECHANIC
On my first use of the boat, the engine ran roughly and seemed to lose power. I took the boat to a local shop. The "fuel injection" was cleaned and the fuel filter was changed. I used the boat again, but there was no change in how the engine ran.

[With the boat back at the local shop] the mechanic measured the fuel pressure and described the measured pressure as "very low." The mechanic surmised the fuel pump in the vapor-separator tank assembly (VST) was bad. The mechanic stated an estimated repair would require four hours of labor and replacement of the pump in the VST. Upon attempting to order OEM parts, after a week's delay the mechanic told me the necessary parts are now obsolete.

FIXING THE PROBLEM MYSELF
With little faith in the mechanic, next I tried to fix the problem myself. I took three initial steps toward a solution:

• I used a portable tank (so as to eliminate the possibility of bad fuel in the main tank being the cause of the poor engine running);
• I changed the fuel line and the primer bulb;
• next, I "opened up" the engine, l got to the VST, I tested the pump on a bench, and I changed the filter [a filter in the VST perhaps], which took half a day and was my first experience at this sort of work, and required removal of the [lower cowling or midsection in order to gain access to a fastener needed to remove the "silencer", the engine block, and the VST;[/list]

I then saw the filter in the VST was about 40-percent "clogged up." This was a disappointment because my hope was to find the filter "clogged up" to 90-percent--or something. I then knew [the 40-percent "clogged up" filter] was not [the cause of the engine running problem].

The engine [was put back to running condition and the boat was tested again]. {The engine continued to] run roughly at idle speed and appeared to be starved for fuel when shifted into gear.

Knowing that the [fundamental cause of the engine poor running was due to starvation of gasoline] I began a process of elimination [to find the cause of the starvation] by [using a method of testing that would] eliminate one [component of the fuel system] at a time.

[The first component of the fuel system I tested in my process of elimination was] the low-pressure fuel pump. I inspected the low-pressure fuel pump.

[The second component of the fuel system I tested in my process of elimination was a hose and primer bulb.] I opened a hose and squeezed the primer bulb: fuel came out "good" without any leak.

Next I made this observation: [downstream] of the low-pressure pump is a "looking-big" fuel line with a heat shield cover, [which I will describe as] the in-line fuel filter [strainer or filter]. Again, I removed a hose and squeezed the primer bulb. Only "a little" fuel came out. I then knew I had found [the cause] of the problem [of fuel starvation in the engine fuel system].

UPDATE TO PRESENT DAY
I bought a non-OEM replacement made by Sierra on Amazon that had fast shipping, I tested the boat. [The problem of poor engine running due to fuel starvation has been remedied, and] the engine [now] runs "like a dream."

I also have ordered the OEM part [and I am waiting] for delivery.


Fig 1: the 2005 Mercury 115 FOURSTROKE engine with cowling and other components removed.


Fig. 2. The partially 'clogged up" filter in the [high-pressure] pump.



Fig 3. The 98-percent "clogged up" in-line fuel filter [or strainer].



Fig. 4. Testing with the new in-line fuel filter [or strainer].

[fno]

That picture of the clogged filter looks to me like the kind of varnish you get with Ethanol mixed fuel sometimes. Not sure but looks like a duck, quacks like a duck. Glad you got to the bottom of it. Fuel starvation is a really bad thing to have.

[jimh]

What is a "fuel trainer"?

Perhaps you mean "strainer."

Please elaborate.

Perhaps you can give a better description of the part or parts you ordered that seem to cure the problem of fuel starvation.

Also, I am interested to know how you tested "the pump" on your bench.

Please explain the method you used to test the pump, and exactly what criterion you used to establish if the pump was working properly on the bench.

[jimh]

In Figure 2 there are two filters shown. I think one filter is a new OEM filter and the other filter is the partially obstructed filter. If that is correct, please emend the caption for Figure 2 to indicate that and also which filter is the new and which is the old.

Also in your narrative you mention a "silencer" that was removed. From the photograph in Figure 1, to me it looks like you removed the fuel-air inlet manifold from the engine block. Is that what you mean by "silencer"?

[jimh]

In Figure 4 I see a very attractive sunset behind a nice Boston Whaler boat, but there is no sign of the fuel "trainer".

[jimh]

Generally in a fuel system there are several stages of filtering. The filters are arranged in a order that enhances their function and prevents obstructions from forming.

Generally in the fuel tank itself there will be a coarse screen on the fuel pick-up tube that will prevent very large debris from getting sucked into the fuel lines.

Downstream of the tank pick-up there will be a large-capacity canister-type spin-on filter that is intended to stop debris and also to separate water from the gasoline fuel. This size of the screen in the filter is generally rated in microns. A typical rating for a large canister type fuel-water separating filter is in the range of 10 to 20 microns.

Downstream of the fuel-water separating filter in engines with carburetors there may not be any further filters. In engine with fuel injectors there will typically be additional fuel filters at the engine.

In fuel injection systems there is typically a fuel distribution manifold in which the fuel is pressurized and maintained at a pre-set pressure. The fuel is also often circulated in a fuel injection system in order to pass through a fuel cooler. Typically in the circulation system there will be additional filters to remove any debris in the fuel that has arrived to the system or possibly debris created within the circulation system by decay of rubber components like hoses or impellers.

The usual design is to decrease the size of the filter screen openings as the fuel flows from the tank to the engine. In this way, each filter removes some debris before the fuel is passed to the next stage of filtering, where typically the filter screen becomes smaller. In this way the chances of large debris getting into the fuel injection pressurized fuel manifold distribution is avoided, and any filters in that system should only have to contend with small-size debris particles. This approach to fuel system filtering prevents small filters in the high-pressure fuel system from being clogged with debris.

If the particular boat under discussion in this thread does not already have a large canister fuel-water separating filter immediately downstream of the fuel pick up hose from the fuel tank, adding a filter like that will reduce the risk that some smaller-capacity finer-screen filter in the high-pressure fuel manifold will become obstructed with debris and prevent proper fuel distribution the fuel injection system.

Preventing loss of fuel pressure or fuel volume available in a fuel-injection engine is very important. If the engine is being starved for fuel, the combustion chamber fuel-air mixing ratio will become lean on fuel. A lean combustion chamber mix results in higher temperatures being produced in the combustion chamber, which can lead to serious engine damage. In a combustion chamber, part of the cooling is produced by the vaporization of the gasoline to vapor from a liquid; the energy needed to vaporize the fuel draws heat from the combustion chamber. When the cooling provide by a reduction in fuel-air mix to be lean on fuel decreases, the combustion chamber temperatures will rise above their normal operating range.

[MisChief15]

Thank you very much Jim for explaining how the fuel in different system works.

Yes strainer not "trainer."

The "silencer" is the fuel-air inlet manifold.

The only part I need now is the Yamaha in-line fuel filter part # 6C5-24251-01-00

Also on my boat, there is a fuel-water separating filter after the fuel tank.

As for the testing the high-pressure fuel pump in the VST, i just removed the pump from the VST assembly, inspected it, then extended the two wire leads and connected them to a small 12-Volt battery.

[jimh]

Regarding adding filters in the fuel delivery path from fuel tank to the engine:

Each filter introduces some loss of pressure, in this case a loss of suction pressure created by the engine's lift pump. On may outboard engines the lift pump will be a diaphragm type pump that is operated by air pulses take off the crankcase. The pump can only tolerate so much pressure loss in the fuel system.

In some installation a pressure gauge will be connected across the input and output ports of a filter, and the pressure drop or loss in pressure across the filter element will be read on this pressure gauge.

Typically, as the filter element in a fuel filter collects and blocks debris in the fuel from flowing through its filter screen element, the total size of unblocked filter screen area is steadily reduced. At some point the amount of unblocked filter screen element area becomes so small that the pressure loss across the filter becomes quite high, and the lift pump can no long suck fuel through the filter screen at a rate that will keep up with the rate of fuel consumption needed by the engine. This also results in fuel starvation problems.

The use of a pressure gauge installed across the filter element is a good method to indicate how much debris has been trapped in the filter, and when the filter needs replacement. On the other hand, the filter elements are not very expensive, and just routine replacement of the filter element at regular intervals can be useful to prevent having a clogged filter.

The element of the fuel system that determines how much debris will need to be removed by filters is the quality of the fuel when it is pumped into the fuel tank. In some instance where the locally available fuel is not particularly free of debris, a filter element is used right at the fuel fill fitting to keep debris in the fuel from even getting into the boat's fuel tank in the first place. If your local gasoline fuel is known to have impurities, pre-filtering the gasoline before it goes into the fuel tank is a good method to avoid fuel debris clogging filters.

An example of a funnel with a built in-filter that can filter gasoline as it is dispensed from the retail fuel pump is seen at

https://mrfunnel.com/Mr._Funnel/Home.html