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Old 25-08-2012, 15:20   #1
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Fuel Tank Pickup

We have 2 fuel tanks, each holding 40 gl. The PO said they only used the stbd tank. I added fuel to the port tank but am having some trouble. When I switch to the port tank, the pressure gauge on the fuel filter immediately rises to about 14 " Hg. When drawing from the stbd tank it reads 0. Also, a steady stream of small bubbles starts to flow into the fuel filter. Eventually, of course, the engine starves for fuel and dies.

I thought I could slowly bleed the air out of the port tank supply line by switching to the port tank, waiting a couple minutes, then switching back to the stbd tank before the engine starves. No such luck. After over a half hour of switching back and forth, still high pressure and little bubbles, but no steady fuel flow.

Before I start pulling fuel lines off and pulling pickup tubes out of the tank, I thought I post here to see if anyone has any experience with this type situation.

thanks!
Greg
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Old 25-08-2012, 15:37   #2
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Re: Fuel Tank Pickup

This is caused from either aiir being in the line from the empty tank or an air leak in the fuel line from the port tank. This may be the reason that the PO never used the port tank.
All air from leaks will accumulate in the injecter pump and can only be removed by bleeding the air from the fuel.
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Old 25-08-2012, 15:39   #3
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Re: Fuel Tank Pickup

hmmmm..... dont think a fuel line air leak would cause high vacuum...? Must be plugged up pickup tube....
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Old 25-08-2012, 16:12   #4
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Re: Fuel Tank Pickup

Quote:
hmmmm..... dont think a fuel line air leak would cause high vacuum...? Must be plugged up pickup tube....
^^^
+1

Did you inspect the tank before adding fuel? It may have had a bunch of grunge in it that got stirred up when the new fuel was added.

I certainly have had problems with a plugged fuel line. The high vacuum could cause a small air leak at a poor connection.
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Old 25-08-2012, 16:41   #5
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The PO actually never used the Port tank after having both tanks replaced. It sounds like the pickup is the most likely suspect. How hard is that to pull and check?
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Old 26-08-2012, 15:04   #6
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Re: Fuel Tank Pickup

usually rather easy. pic?
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Old 26-08-2012, 15:09   #7
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Re: Fuel Tank Pickup

Is the Port tank vented?
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Old 26-08-2012, 16:27   #8
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Re: Fuel Tank Pickup

Update. I disconnected the fuel supply line from the port tank at the selector switch. Then I connected an air pump to test the line - no clogs - heard plenty of bubbles coming out in the tank. So I'm guessing it's just that hard to pull the air out of the line. The fuel pump has a lever to prime the system, but it was taking forever. So next step is to backfill the supply line with diesel by pouring it in at the selector valve and then bleeding the fuel system at the injectors to remove any remaining air in the lines. Ran out of time tonight so will pick it up next trip to the dock.
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Old 26-08-2012, 16:38   #9
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Re: Fuel Tank Pickup

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Originally Posted by perchance View Post
Is the Port tank vented?
VERY GOOD THOUGHT! Check the vent inlet for bee nests/dead bees... especially if you are in the south....
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Old 26-08-2012, 16:38   #10
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Re: Fuel Tank Pickup

As perchance said ck the vent line for obstuctions or kinks and the fuel outlet for plugs or loose connections!! Could be both or maybe he never had a vent ? ya gotta ck to be sure ! hope ya get it cured cus it's so nice to have extra fuel!! ya may need a manifold to redirect the fuel to and from the tanks it's nice to be able to let the return go where ya want it sometimes for ballast,or with an extra filter to help keep it clean ! just a thought
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Old 26-08-2012, 16:45   #11
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Re: Fuel Tank Pickup

Hmm - good thought about the vent. Will check. Thanks for the advice.

The manifold has separate selector valves for the supply and return lines. So I can draw from one tank and return to the other. Agree that's a nice feature. Now if can just get both tanks to draw...
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Old 26-08-2012, 22:34   #12
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Re: Fuel Tank Pickup

Since the vacuum gauge goes to 14 inches immediatly, it is highly unlikly that it is a vent problem. Fuel goes out of a tank so slowly that it takes a while to create a vacuem even if the vent is clogged. Blowing air back through the line tells you that the line is not plugged, but the air will go through even if there is a lot of crud in the bottom of the tank. When you want the fuel to flow the other way, the crud settles again and replugs the pickup line. If you can get a small hose into the tank(all the way to the bottom) and pump a quart or 2 into a clear jug you will probably see lots of crud. More than likly you need to have the tank polished. The previous owner didnt use just one tank becouse it was convenient. Were they really replaced? Look at the mountings of the two tanks and see if one looks like new work and one looks undisturbed. One other thing, if you go ahead and pull the pickup tube from the tank and it has one of those fine mesh screens on it, THROW THE SCREEN OUT. It is much easier to change a fuel filter at sea than it is to pull a pickup tube in a rolling boat. The main filter is for the purpose of catching the crud.____Good Luck____Grant.
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Old 27-08-2012, 07:33   #13
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Re: Fuel Tank Pickup

Quote:
Originally Posted by gjordan View Post
Since the vacuum gauge goes to 14 inches immediatly, it is highly unlikly that it is a vent problem. Fuel goes out of a tank so slowly that it takes a while to create a vacuem even if the vent is clogged. Blowing air back through the line tells you that the line is not plugged, but the air will go through even if there is a lot of crud in the bottom of the tank. When you want the fuel to flow the other way, the crud settles again and replugs the pickup line. If you can get a small hose into the tank(all the way to the bottom) and pump a quart or 2 into a clear jug you will probably see lots of crud. More than likly you need to have the tank polished. The previous owner didnt use just one tank becouse it was convenient. Were they really replaced? Look at the mountings of the two tanks and see if one looks like new work and one looks undisturbed. One other thing, if you go ahead and pull the pickup tube from the tank and it has one of those fine mesh screens on it, THROW THE SCREEN OUT. It is much easier to change a fuel filter at sea than it is to pull a pickup tube in a rolling boat. The main filter is for the purpose of catching the crud.____Good Luck____Grant.
Good Advice. To add my 5c worth, make sure that IF you invest in a fuel polishing exercise, that they get to the crud on the bottom and around the baffles, which may be impractical depending on the design of the tank. I've had 2 boats arrive in Baltimore harbor lose engines after having their tanks polished in Annapolis. Plugged fuel lines. On one I had to use a car pump to forcefully blow back the slug in the line - which is a case for having SOME KIND of filter on the fuel suction pipe. (I've used insect screen netting shaped in a ball in the past.). What is the point in polishing clean fuel when all the bad stuff has fallen to the bottom of the tank? Some tank cleaners (but not all) make a point of dealing with the tank bottoms where possible.

On my boat I stick a hose through the fuel level sender aperture with a suction pump. I have a small dia. hose wired to a stick to enable some movement along the bottom. When I first got the boat, I pulled out 3/4 gallons of mud in the 30 gallon tank this way. This setup also is a quick and easy way of stripping any condensation or other stuff that's settled over winter. The tank is set on the keel so there's no way to drain it other than pump it out.
Another tip that's slightly off topic is to add a squeeze pump to the fuel line, which makes it really easy to refill the racor and eliminates a whole lot of bleeding with the lift pump.
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Old 27-08-2012, 07:47   #14
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Re: Fuel Tank Pickup

Quote:
Originally Posted by gjordan View Post
Since the vacuum gauge goes to 14 inches immediatly, it is highly unlikly that it is a vent problem. Fuel goes out of a tank so slowly that it takes a while to create a vacuem even if the vent is clogged. Blowing air back through the line tells you that the line is not plugged, but the air will go through even if there is a lot of crud in the bottom of the tank. When you want the fuel to flow the other way, the crud settles again and replugs the pickup line. If you can get a small hose into the tank(all the way to the bottom) and pump a quart or 2 into a clear jug you will probably see lots of crud. More than likly you need to have the tank polished. The previous owner didnt use just one tank becouse it was convenient. Were they really replaced? Look at the mountings of the two tanks and see if one looks like new work and one looks undisturbed. One other thing, if you go ahead and pull the pickup tube from the tank and it has one of those fine mesh screens on it, THROW THE SCREEN OUT. It is much easier to change a fuel filter at sea than it is to pull a pickup tube in a rolling boat. The main filter is for the purpose of catching the crud.____Good Luck____Grant.
Good advice. Especially the part about the small hose into the bottom of the tank. When I first got my boat I used a suction pump through the fuel sender hole in the tank and pulled out 3/4 gallons of mud from the bottom. The fuel was clean, too. I've seen 2 cases of boats losing power in Baltimore harbor after having fuel polished in Annapolis the same week. On one boat I had to use a tire pump to blow the slug of stuff in the fuel line back into the tank. Which makes a case for SOME KIND of fuel screen on the intake line. I've used screen netting shaped to a large ball in the past. BTW, what's the point in polishing clean fuel when all the problems lie on the bottom of the tank? Some fuel polishers make a point of trying to get to the crud on the bottom, but not all.

Quick tip, slightly off topic...add a squeeze pump to the fuel line out of the tank. Makes checking the line, refilling the racor and bleeding the whole line a cinch.
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Old 03-09-2012, 15:55   #15
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Re: Fuel Tank Pickup

Update. Some more data, lots more questions. Here's the latest on the troubleshooting efforts.

Checked the vent line - all clear. Then I used an electric fuel pump hooked up to the selector valve end of the port tank supply line. Pumped fuel out with no problem. While pumping, squeezed off the supply line and then quickly reattached it to the selector valve. When I started the engine, there was some pressure on the guage, but not the 14" previously. But then the vacuum gradually grew back up the 14" Hg.

Net pulled the pickup. Nothing fouling it, no screen on the end.

One interesting tidbit. The end fitting on the supply line has a fairly small (maybe 1/16") hole for the fuel to pass thru. But the stbd side which works fine, has the same fitting. But maybe the port side fitting is constricted somehow and the electric pump was just strong enough to force the fuel through the orifice??

I think it's narrowed down to 2 components:

- the fuel line may have some constriction somewhere (includes the fitting question)

- the tank selector valve may be clogged somehow (although I've never heard of that)

My planned next troubleshooting step is to buy a new length of fuel hose (long enough to replace the entire old line) and connect it between the tank and the selector switch. If that solves it, then replace the fuel line. If not, then it's gotta be the selector switch.

Thoughts? Other ideas?

BTW- I borrowed the electric fuel pump from a friend in the anchorage. It was handy enough that I've decided to go to Autozone and buy one to keep in the onboard stores just in case.

Thanks!
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