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Old 05-11-2015, 10:59 AM   #1
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Air in fuel line FL 135

So I'm having this problem, every 10-15 hours my engine will die. I pop the bleed screws on the fuel filters and it is pressurized with air. Bleed it out and it runs fine for another period of time, as bad as 2 hours but usually 10 or so. So I replaced the racor filter and seals, the fuel filters and seals, the seals that go into and out of the filter housings, and I still have the same issue. I found that my lift pump housing was cracked, figured that was the problem so replaced it. Nope, same issue.......This engines (2725e) fuel return line does not go back to the fuel tank, it goes, uh, somewhere else, not sure exactly, guess it just loops back around and tries again, for lack of understanding. Anyway I take that line off after the injection manifold and I have air in that line too. So I'm just not sure where to look for this air leak at this point. Was hoping someone had been thru a similar senario and could point me in a direction to explore. My next option would probably be to replace the racor unit, I did drop it once, but it does not leak fuel so... I can get the engine running in less than 2 minutes, but if it ever happened while I was docking, well, that would be very bad. Ideas?
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Old 05-11-2015, 11:19 AM   #2
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You could put a squeeze bulb before your Racor, pump it up and use soapy water sprayed on all the lines and fittings to see where the leak is. You could have a small crack in one of the lines. I had the same issue and found the inlet fitting to the lift pump was cracked, it would only leak when running. Also, when it happens, take the top off the Racor and see if the fuel level is low enough that air would get in the outlet. If so, the problem is upstream.


Regarding the fuel return. I believe it should go back to the tank otherwise it will be hot if it goes back directly to the engine.
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Old 05-11-2015, 05:55 PM   #3
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I think I would start with the fuel return line. If it really loops back to the fuel supply somewhere that could be a real problem. It needs to go back to the fuel tank.


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Old 05-11-2015, 06:42 PM   #4
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Well I'll take a look at the return line tomorrow. 100% sure it never went back to a fuel tank though. Would be nice if it did since it could spit that air out at that point. I'll try and take some pictures of the set up. the 135 is a little different than the 120.
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Old 05-11-2015, 07:17 PM   #5
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Having it go back to the tank won't help if the leak is someplace else. The air will hit the injector pump first and starve the engine.
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Old 05-12-2015, 09:15 PM   #6
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Ok got some pictures today of the layout. Here is the return line setup.

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comes out of the injection manifold and comes back around to the last picture, and goes into a fitting on the engine block. Have no idea where it goes from there, but it has to be trying to put fuel into the injectors I would guess. you can see the fitting going into the rear corner of the block just below the silver cap. Don't know where to go from here..........
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Old 05-12-2015, 09:22 PM   #7
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Not familiar with that engine, but on my SP225s that fitting in the head is a return line from the injectors. It returns to the tank as well as the line from the injection pump.


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Old 05-12-2015, 09:25 PM   #8
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Those are engine oil feed and return to lubricate the injector pump, not fuel. That was one of the advantages of the 135 over the 120
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Old 05-12-2015, 09:34 PM   #9
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In the first pic on the bottom left you can see the oil line for the injection pump, but I assure you there is diesel in the line I'm talking about. And air...
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Old 05-12-2015, 09:38 PM   #10
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Guess I could pull the lid off and see where it goes...... Maybe thursday I'll do that, playing golf tomorrow cause thats not frustrating at all. ha
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Old 05-12-2015, 09:46 PM   #11
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The bottom photo is where the Lehman 120 has the fuel return from the injectors as you described and BobH.
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Old 05-12-2015, 10:01 PM   #12
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You are right. I found the Lehman 135 manual on the GB forum but I can't copy the page that has the diagram. Sign up, it's a good site.


There is a return line from the Simms injector pump and a return line from the injectors themselves but they are under the rocker cover.
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Old 05-13-2015, 01:11 AM   #13
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Looks like your injector leak off return from cylinder head is tied right to injection pump. But not sure if I am following things right. Injector leak off and pump return should tee together and go back to the tank. Not sure if the Lehman has a wierd flow path, but what is described above is typical for most diesels. If air has no way to vent back to the tank, it will build up in pump and eventually stall engine.
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Old 05-13-2015, 08:55 AM   #14
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Get in touch with American Diesel. They are the experts on FLs.


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Old 05-14-2015, 12:39 PM   #15
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Some confusion here. Let me try to help. In the picture below, #1 is the fuel line into the injector pump. #2 is the fuel return line OUT of the injector pump. #3 is the lubricating oil line into the injector pump.
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Old 05-14-2015, 12:45 PM   #16
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The item circled in this picture is the fuel return from the injectors. It is usually T'd to the return line from the injector pump and they both MUST go back to the tank.
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Old 05-14-2015, 02:02 PM   #17
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I see the problem, running Perkins filters on a FL. For shame! But as kchace wrote, that is return line from the injectors and needs to go back to the tank along with the return from the injection pump.


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Old 05-14-2015, 05:30 PM   #18
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Thanks for the info guys. I'm gonna plumb in a return line tomorrow. Funny its been set up this way since it was installed in 96 i would guess. I'll let the forum know how it goes after a few 20 or so hours. Thanks again
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Old 05-14-2015, 05:51 PM   #19
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Greetings,
Mr. W. Didn't review the whole thread and it may have been mentioned but did you consider the inside of your fuel line may be collapsing under suction and your pump is sucking on a previously negligible air leak? Had a problem a couple of years ago similar to yours where the engine would run on the fuel in the Racor then die after about 1/2 hour or so. Chased phantom air "leaks" around for days. Changed the fuel line (about $10 and 15 minutes work) and no more problems. Instant fix!
Since you mention your engine has been running well since '96, the way it's plumbed now, it's unlikely addition of a return, while NOT a bad idea, will cure your problem. Just my $.02...
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Old 05-14-2015, 05:53 PM   #20
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If it has been that way since 1996, are you sure that's the source of the air in the system? It's been sugested before (Ski maybe), to plumb a section of clear tygon tubing before the engine filters and look for air bubbles. If so, work your way back toward the tank. My guess is you have a small air leak at the racors and/or a fitting before the engine.
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