Vacuum Lock in Fuel System in 2014 170 DAUNTLESS

[williamlv17]

My 2014 170 DAUNTLESS has a fuel system venting problem. A vacuum is being created and restricting fuel flow to the propulsion engine as the engine runs over time.

Opening the fuel-filler inlet cap relieves the pressure from the vacuum.

The engine speed drops briefly at WOT on an intermittent basis. On occasion there is a complete loss of engine power. The vacuum lock won't allow [the engine] to restart unless the fuel cap os opened to vent the [negative pressure of the vacuum].

As a first step in creating a remedy, I replaced the fuel demand valve. Replacing the fuel demand valve helped a bit.

In the 2023 boating season, I could only operate the boat for 40-minutes before vacuum locking occurred. Now I can go more than five hours without a complete vacuum lock. But I still experience a reduction in engine speed (without [throttle] input) and there is still some vacuum happening because [I can hear] air rushing in when I open the fuel filler cap to relieve the pressure.

Due to this, my next step is going to be replacing the fuel filler neck and fuel filler cap because I believe it is supposed to vent fuel vapor when pressure builds.

I have checked the two in-line fuel filters at the lower portion of the engine and replaced them. I have tested the fuel and run a few bottles of HEET through the last few tanks, so I know there's no [cause of this problem due to] the fuel.

Give me your thoughts or ideas on what it could be [the creation of a vacuum in the fuel system that] I [have overlooked].


A diagram of the fuel setup is shown below. The fuel system uses EPA compliant"Attwood equipment designed to keep fuel vapors from escaping into the air.

I haven't been able to locate a part number one more filter. I need help identifying the filter shown below in a photograph.The filter in-line with the vent for pressure relief at the top of the engine. I'm think this filter may be a fuel/vapor separator. I can't locate it on the Mercury fuel system diagrams.

FFIg. 1 Filter in-line with vent pressure relief cap

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Fig. 2. Better view of filter seen in Figure 1/

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Fig. 3. Dauntless 170 Fuel System Diagram

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[jimh]

Some Boston Whaler boat of that epoch used a fuel tank venting system in which the vent hose was run to the fuel filler inlet fitting. Boats with that configuration of the vent in the fuel filler fitting are somewhat notorious for problems.

The factory remedy for these problems was to create a separate fuel tank venting outlet that was a through-hull fitting installed well above the water line on the hull sides.

[williamlv17]

Some Boston Whaler boat of that epoch used a fuel tank venting system in which the vent hose was run to the fuel filler inlet fitting. Boats with that configuration of the vent in the fuel filler fitting are somewhat notorious for problems.

The factory remedy for these problems was to create a separate fuel tank venting outlet that was a through-hull fitting installed well above the water line on the hull sides.

I see, thank you. Did they go to a new fuel filler neck design as well then? Since this current one is integrated with the ventilation line and I assume a carbon canister?

[jimh]

Did [Boston Whaler change the fuel filler on some DAUNTLESS models] to a new fuel filler neck design as well...?

As I mentioned in my reply above, the remedy was to install a separate fuel tank vent fitting and route the vent hose to that separate fuel tank vent fitting, as was done on most every other Boston Whaler boat made. Let me also repeat my earlier advice:

The factory remedy for these problems was to create a separate fuel tank venting outlet that was a through-hull fitting installed well above the water line on the hull sides.

Since this current one is integrated with the ventilation line and I assume a carbon canister?

I have no information about use of any device called "a carbon canister" in any marine application of fuel tank venting on Boston Whaler. Perhaps you are confusing federal regulations that apply to small outboard-powered boats with federal regulations that apply to automobiles.

The federal government entity The Environmental Protection Agency--as all federal government agencies tend to continually do--expanded the reach of their remit to regulate air pollution to apply to certain types of fuel tanks used on boats to restrict the ability of such tanks to be openly vented to the atmosphere. If you want to learn more about recent federal regulations that apply to boat builders regarding how the below-deck gasoline fuel tanks must be vented to the atmosphere, you can pursue that topic. My interest in that topic is not particularly acute so the knowledge iIhave to share is only cursory.

[jimh]

Also, because a 2014 boat is just ten-years-old, you should be able to get support from the Boston Whaler factory regarding the problem of vacuum lock in the fuel system. I would contact Boston Whaler directly to see if they can offer any useful advice. They may just direct you to their local authorized dealer, which is probably only useful advice for that dealer, as he will probably see the remedy to this problem as a source of billing a customer for work. But you never know, as there could be a factory-supported remedy that the dealer could implement for you at no cost.

[Phil T]

Do not expect support from Whaler unless this is a warranty item.

Only models in current production will get service from Customer Support.

I would remove the integrated fill/vent cap and install a separate fill and vent fittings. The vent goes through the gunwale approximately 1-1/2 inches below the bottom edge of the rubrail.

https://www.wholesalemarine.com/moeller-marine-chrome-thru-hull-fuel-tank-vent.html

Fig. 4. A Moeller thru-hull vent fitting

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[jimh]

You should temporarily disconnect the fuel tank vent from the fuel filler fitting, then just retain it some where so it is open to the air, then see if that cures the vacuum lock condition you have been experiencing. It the temporary open vent of the fuel tank works to solve the problem, then get a vent fitting (as Phil T mentions above) and make it a permanent change.

[williamlv17]

I have no information about use of any device called "a carbon canister" in any marine application of fuel tank venting on Boston Whaler. Perhaps you are confusing federal regulations that apply to small outboard-powered boats with federal regulations that apply to automobiles.

There apparently was ["a carbon canister device" in Boston Whaler boats] for a few years. See attached photo.This is the angled fuel filler neck I have from Attwood:

Fig. 5. Advertisement for fuel filler.

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Here is their description of its function fron manufacturer Attwood:

"CARB and EPA compliant deck fill for systems with carbon canisters.

Fuel systems have evolved in recent years; EPA and CARB requirements limit fuel emissions and protect the environment, but they also present new challenges to boaters. Fortunately, Attwood has done a lot of the work to help make staying compliant easier. These deckfills are designed to work with modern fuel systems with an incorporated carbon canister and have the same footprint of traditional hinged deckfills. The hinged scalloped cap has an integrated pressure relief valve and features an audible click that indicates when the cap is locked in the closed position. The body is engineered to be compatible with vapor recovery nozzles to meet CARB Phase II requirements. All of the components of these deckfills are compatible with ethanol blended fuels. The cap was designed to effectively prevent water from entering the fuel system. For straight forward solution to today’s complex fuel systems, let Attwood provide a solution.

Key Features

EPA and CARB compliant
Cap features audible click and dual overpressure relief valves
Deckfill body is engineered to meet nozzle mating and vapor recovery requirements
Meets Phase II CARB nozzle retention and automatic shut-off standards (when part of a complete Attwood system)
Compatible with ethanol blended fuels
Integrated spark and flame arrestor
Chrome plated scalloped cap design
Two-year warranty

[jimh]

There apparently was ["a carbon canister device" in Boston Whaler boats] for a few years....This is the angled fuel filler neck I have from Attwood

Are saying that on your 2014 170 DAUNTLESS as delivered from Boston Whaler the fuel filler inlet was of the type you show that appears to incorporate a carbon canister?

As I stated, I had no knowledge about use of carbon canister filters in the fuel system of Boston Whaler boats, and when I said that, that was completely truthful. As it turns out, I was completely unaware of an EPA mandate that was created in July 2011 and thus would have affected Boston Whaler boats built after July 31, 2011. I just discovered this amazing overreach of the government this morning when a search for the phrase "when did EPA mandate carbon canister filters" found this citation:

PART 1060—CONTROL OF EVAPORATIVE EMISSIONS FROM NEW AND IN-USE NONROAD AND STATIONARY EQUIPMENT
https://www.ecfr.gov/current/title-40/c ... /part-1060

I am sure there must be something even more outlandish required in California by the California Air Resources Board (CARB) who seem intent on removing the last molecule of emission from any device that uses gasoline as a fuel.

But all of this diversion into carbon canisters aside, are you going to try my suggestion to disconnect the vent line to the fuel filler and see it that affects the problem you describe as "vacuum lock" in the fuel system of your 2014 170 DAUNTLESS? You better not answer that in case the EPA are reading this thread.

[williamlv17]

Are saying that on your 2014 170 DAUNTLESS as delivered from Boston Whaler the fuel filler inlet was of the type you show that appears to incorporate a carbon canister?

Yes, that is the factory setup for my 2014 [170 DAUNTLESS]. [The fuel filler inlet and vent assembly] is an ATTWOOD system designed to comply with EPA guidelines and prevent unnecessary fuel vapor release.

I hope they’ve improved the design since 2014, and maybe this was only around for a few years

...are you going to try my suggestion to disconnect the vent line to the fuel filler and see it that affects the problem you describe as "vacuum lock" in the fuel system of your 2014 170 DAUNTLESS? You better not answer that in case the EPA are reading this thread.

Haha.

If the factory fix was to install a [separate] vent, then I’m definitely going to explore that [modification]

I suppose I will start with replacing the fuel filler "neck" that I referenced.