Air in Fuel System Puzzle

[Dockhead]

Originally Posted by Kenomac

Did you try what I suggested? If the engine fuel lines are still hooked up along with the generator, air will be sucked into the generator fuel lines via the engine lines or air will be sucked out of the generator lines.

When was the last time you changed all your fuel lines?

Hi Ken: The fuel lines were never connected with the main engine. I disconnected the main engine first.

Fuel lines have never been changed, but are pliable and not cracking. I might substitute some new hose, though, just to be sure.

[boeing1]

had similar problem on a friends boat turned out to be a blockage in the fuel line at a elbow, also not sure what kind of electric fuel pump you have some of them have filters,

[Kenomac]

Originally Posted by Dockhead

Hi Ken: The fuel lines were never connected with the main engine. I disconnected the main engine first.

Fuel lines have never been changed, but are pliable and not cracking. I might substitute some new hose, though, just to be sure.

Bingo! Your nearly twenty year old, dried out fuel lines are your problem. You're "chasing your tail" if you don't start by changing all the fuel hoses. It's a three hour DIY, long overdo project. Our boats are the same age, and last year... my fuel hoses were trash.

[SecondBase]

Originally Posted by Kenomac

Bingo! Your nearly twenty year old, dried out fuel lines are your problem. You're "chasing your tail" if you don't start by changing all the fuel hoses. It's a three hour DIY, long overdo project. Our boats are the same age, and last year... my fuel hoses were trash.

At $12/foot I'm wishing I had replaced mine as well now a while back. For me at least they fell into a blind spot by not being "engine" wear parts.

[Russ]

Been there with air leaks.
The ONLY way of being sure of identifying the leaks is to wrap a piece of paper towel around every fuel fitting. Then, since a diesel SUCKS fuel you need to hook up a small fuel quality pump at the tank exit fitting to PUMP fuel through the system and look for staining on paper towels and fix those leak points. This is all a Pain but the only way I found my leak!

Merely wrapping the paper towels and running the engine can work but again since a diesel engine sucks fuel it may not show ALL the leak points for certain.

Russ

[svseawitch]

We had the same problem that drove us nuts for a month. swapped out the fuel selector valve after talking to a guy that had seen air leaks in fuel valves. I never thought the valve could suck air through the body

[SecondBase]

Originally Posted by svseawitch

We had the same problem that drove us nuts for a month. swapped out the fuel selector valve after talking to a guy that had seen air leaks in fuel valves. I never thought the valve could suck air through the body

So putting the comments of Russ and Seawitch together. If you can wrap and over pressure that's best. If out cruising and you can't overpressure maybe isolate one component at a time from tank to cylinder until you locate the fault?

I have twin fuel tanks so I'll start by changing the attachment at the tank from P to S.

[cptcptcpt]

a quick way to find e leak is to disconnect a line and blow into it. if you dont hear bubbles or hissing then reconnect it and blow into the other end. a new longer hose makes it easier

filter container leaks are most common

[SecondBase]

Originally Posted by cptcptcpt

a quick way to find e leak is to disconnect a line and blow into it. if you dont hear bubbles or hissing then reconnect it and blow into the other end. a new longer hose makes it easier

filter container leaks are most common

This is why we love the forum. Thank you!

[elandra65]

Some good suggestions here. Using a container to gravity feed clean fuel direct to injection pump would be my start point. Then add the components until the problem is identified. One other possibility which happened to me last year on my Volvo MD22 is if an injector is held open by a foreign object it will fill the injector pump with gases on the compression stroke thereby stopping the engine. You can bleed it again but it will only run for a minute before it aerates and stops. Took quite a lot of trouble shooting to work out the problem. Good luck

Andrew

[charliehows]

I've said this before but it's worth repeating – considering the tiny cost of fuel supply line components, if anything in your fuel supply line is more than a few years old (and ESPECIALLY if you dont know how old it is) REPLACE IT if you are having air leak problems. Special mention goes to fuel tank taps – no-one ever suspects them but mine failed; o-ring seals on filters; for the tiny cost of flexi fuel hose and clamps, if-in-doubt-swap-it-out; the whole lot from tank through to injectors can be replaced for less than the cost of a decent restaurant outing.

[decktapper]

Hello Dockhead:
It sounds to me like as someone said, the problem is before your fuel pump or may be your fuel pump.
This may be a stupid question, but as much trouble as we have with fuel on boats, how come you almost never see even one high quality gauge on the fuel system?
It sounds to me like you have a fuel tank, tubing, possibly valves, and then a fuel pump, from there it goes to your first fuel filter. If that is correct, I think I would install a Dwyer Magnehelic on the suction side of the fuel pump, I would also install at least one pressure gauge somewhere on the output side of the fuel pump, if it was just one, it would be on the output side of the fuel filter.
If there are serious downsides to this, anyone please educate me.
Thanks and good luck.
decktapper

[transmitterdan]

Most boats with Racor filters have (or can easily install) a vacuum gauge down stream of the filter. If there is one then close the valve allowing fuel into the Racor. Crank the engine with the stop switch engaged so it will not start. There should be a vacuum registered that does not bleed off. If it bleeds off there is a leak somewhere.

[Terra Nova]

Originally Posted by Dockhead

...the bearings failed on my alternator...
the primary filter must be clogged. I was supposed to replace it before leaving, but received the wrong part...

Questions:

Why do you not carry a spare alternator?

Why do you not carry (at all times) spare filters?

Why do you not employ a professional marine diesel mechanic to maintain your boat in seaworthy condition? (sounds long overdue for routine hose, etc, replacement)

Regarding emergency repairs in the middle of the North Sea, setup a gravity feed day tank to get your generator running.

[Kenomac]

Originally Posted by Terra Nova

Questions:

Why do you not carry a spare alternator?

Why do you not carry (at all times) spare filters?

Why do you not employ a professional marine diesel mechanic to maintain your boat in seaworthy condition? (sounds long overdue for routine hose, etc, replacement)

Regarding emergency repairs in the middle of the North Sea, setup a gravity feed day tank to get your generator running.

I would also add spare starter motors and water pumps for the main engine and generator along with a fuel polishing system to the list. Must haves on our boat. We don't carry a spare alternator, because we have the redundancy of solar, the generator and two alternators on the engine.