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Old 08-30-2020, 08:02 AM   #1
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Red face Intermittent air in secondary fuel filter

Twice since I purchased this trawler 6 months ago, my Lehman 120 will get air in the secondary fuel filters, usually the forward one and engine quits. I bleed the system and everything is fine. My lift pumps lever seems like it’s not pumping much. Feels like there’s no pressure. Wondering if this is the issue. Any info would be greatly appreciated.
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Old 08-30-2020, 08:50 AM   #2
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Having a "dead" feeling lift pump once can often be just the fact that the cam is not properly positioned, Just give the engine starter a little bump. If it always feels funny I think you have found the problem, replace the pump. It is easy and cheap.

Your problem is on the pressure side of the pump. I guess you could check and tighten all your fittings but since your problem is on the pressure side you more than likely would have a leak if something was loose.

Sounds like the lift pump.

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Old 08-30-2020, 09:38 AM   #3
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Pete-Curious as to why you think the leak is on the pressure side? I have a similar problem with just one of my Lehmans. Have had it for 16 years. It seems amazing how much air can get in that secondary filter and still have the engine run. I've never been able to find the leak and just bleed it every 30-40 hrs. I have an electric pump which makes it a lot easier.

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Old 08-30-2020, 11:12 AM   #4
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Following up on Tator's comment about the pressure side, no, air does not leak in downstream of the pump. Air leaks in from upstream. Check and tighten all of the fittings through the primary filter and back to the tank.

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Old 08-30-2020, 11:33 AM   #5
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If the leak is on the pressure side, you'd have dripping/weeping fuel.

To find leaks upstream of the pump, disconnect the hose at the tank outlet and install an electric fuel pump there and a short temporary hose from pump to tank.

Run that and the fuel should drip out of leaks.
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Old 08-30-2020, 11:41 AM   #6
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Talking Need to bleed

Thanks for the great info.
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Old 09-03-2020, 06:47 AM   #7
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"To find leaks upstream of the pump, disconnect the hose at the tank outlet and install an electric fuel pump there and a short temporary hose from pump to tank."

That works well , but to simply find a fuel leak a pail of fuel or an outboard tank and a hand bulb will pressurize the system .

Torn strips of paper towel, on each fitting , and especially around the top of the filter will find even a tiny air leak , by dripping fuel when under pressure.
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Old 09-03-2020, 06:56 AM   #8
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When I first bought my boat, the Lehman would get air every 5 to 8 running hours. I went thru 12 filters on my delivery voyage from Rochester, NY to Mystic, CT.
Bottom line, I replaced the lift pump and the flexible line going to it as it came with the "kit" from ADC.
It was the rubber fuel line that had delaminated internally and was sealing itself shut after x amount of time, coupled with a weak lift pump.
Never had another problem once those were replaced.
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Old 09-03-2020, 10:30 AM   #9
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Not true. My single Lehman went through a period where it stopped cold. It drove me mad as I had done some mods to the fuel system which I was very pleased with. I checked and re-did all my work and was pulling Most of my hair out and one day, while sitting in the engine room, really despairing my decision to be a boater,(!) a tiny bubble of fuel appeared as if by magic on a tiny screw on the injection pump. Eureka! I removed the screw, replaced the copper washer with a fresh soft copper washer and she never missed a beat after that. It would suck air in over an hour or two until there was too much then she’d quit. There was no sign of leakage.
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Old 09-03-2020, 12:25 PM   #10
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Ah yes, those little invisible copper washers!

Then there is the hidden o ring (or is it the square one) under the rim of the cav housing that must be seated within microns.

Clearly an English design.
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Old 09-03-2020, 02:42 PM   #11
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Depending somewhat on the engineroom temp, after running and shut down, the fuel after the lift pump is under a few pounds pressure. As the fuel in the lines and filter cool, it can create a vacuum, drawing air into the system. Usually from the filter gasket or bleed screws.
I chased this problem for a friend on a Lehman over a couple days. It was drawing in air mostly at the secondary filter gasket and slightly at the bleed screw. The bleed screw only leaked when after running and the boat experienced the cold of a winter night.
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