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Fuel filter issues?

Truck Shop

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CO if it takes three weeks to create the problem again I seriously doubt it's a fuel line issue. How much fuel are you using and how many hours a day does it run? How often do you fuel it? Have you checked the vent?
You say this crane sat for a long period. I would install a quarter turn valve at the primary filter on hose from tank, Shut the fuel off each night after use and see what happens.
 

crane operator

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Crane will usually burn 40-70 gallons a day, depending how far we drive and how long of a job it is that day. Most jobs take 5-8 hours start to finish. Probably average 2-3 jobs a week. I fuel daily if its parked on a jobsite, (100 gallon tank) if it goes to a one day job and comes home, it gets fueled when it drives into the shop yard.

Crane does a lot of idling on jobsite work, driving is pulling hard. Crane had sat for a year and a half before I purchased it, I've had it 8 months or so now.

On the vent, it has a plastic german fuel tank cap that's a piece of junk, it doesn't attach very tight. I have a new cap for it, but its a different design locking cap, that you have to use the key on to open and shut. I haven't modified the key structure on it yet. The cap is flat on the upper deck where everyone walks mounting counterweight, so if the key stays in, its getting broken off. Multiple people fuel, so I can't just have the key in my pocket either.

I like the valve shut off idea also. I'll have to figure out what threads are on the line, all the hydraulics are DIN fittings, not readily available. I don't know what the fuel lines are, most likely metric of some kind. The other issue with a shut off at the filter, the filters are under a 4'x4' panel, that's right under the counterweights, not exactly easy access, but every problem has a solution. Maybe at the top of the tank, and a access hole in the deck.

Its done the three- four week after changing filters then losing prime event three times now. New fuel filters instantly cure the problem. Before we changed the filters last week, it would lose prime over a 1/2 hour lunch.

Just for reference, its common to leave it with counterweights on spun to the rear, or else with the boom laid down over the nose like how we drive it down the road. With the counterweights over the rear, fuel filter access is impossible, without something else to drag the crane around, and releasing the swing brake pressure. Its why I'd kinda like to get it sorted out, before it dies and it won't restart with cranking, that's when I'm really going to have issues. :rolleyes:

Pictures should give a idea of covers/ access and locations. The upper cover panel with the black handles I remove daily for checking oil, its not bad to remove, kinda tight if the boom is in the rest. The lower panel is above the filters, and its a little worse if the boom is in the rest, but would be really difficult if the counterweight is on top of it.

20191029_080407.jpg 20191029_080407_LI.jpg 20190516_160249_LI.jpg 20190516_164639.jpg
 

Ronsii

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New filters cure problem!!!! I should have realized this earlier :) once you change the first filter it reduces the amount of vacuum the pump will be pulling against that filter as the filter get a little dirty and restrictive the system starts to pull air from somewhere between that filter and the pump.... right????
 

Welder Dave

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Could something in the filter be breaking down after a few weeks that is causing the filter to drain back? I think I read where some people have installed an electric fuel pump to help prime. Maybe that would be an easy option with a switch on the dash?
 

crane operator

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New filters cure problem!!!! I should have realized this earlier :) once you change the first filter it reduces the amount of vacuum the pump will be pulling against that filter as the filter get a little dirty and restrictive the system starts to pull air from somewhere between that filter and the pump.... right????


Makes sense if the pump pulling is causing the air leak. But to me, the action (fuel siphon back to tank) is happening when there is no movement/ flow in the system.

Crane shuts off, flow back/ check valve on lift pump shuts, trapping fuel in lift pump and secondary filter. Primary filter is on the other side of that check valve, so yes the leak must be there, allowing air in (if the check valve is working like its supposed to), so that fuel can flow back to the tank. But why would changing filters stop it from flowing back?

If the pump is causing the air leak, pulling on a dirty filter, I should see the condition all the time, especially when the pump is running flowing fuel, it should be leaking fuel out- or just sucking air because it can't pull fuel, not letting air in in that condition. Maybe? (Imagine me reaching for more straws here)

I know this is going to be one of those issues that when I figure it out I'll smack myself in the forehead. Truck shops shut off valve behind the primary filter would stop the flow back to tank, but I can't access that point.

Maybe a secondary check valve, right at tank or at entrance/ mounting base to primary filter? I have a check valve right at the top of the lift tube on the outside of the tank, on of one of my older truck cranes.
 

Ronsii

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But..... if an excessive amount of air getting in the system is contributing to the leakback... is kinda what I was thinking.


I agree a second shutoff would be handy... if for nothing else to eliminate one more possibility.


Have had machines that would be hard starting and didn't realize it til' I noticed air in the strainer once... you couldn't see it while running but it kept a small amount in the top then when you shut it off the air would settle back to the strainer(water sep.) so when you started it it'd run for a few seconds the quit... and that put a bunch of air in the IP then it was time to crank for 20-30 secs to get it running again :(

Basically it would run ok with all that air moving through the system but once you shut if off the air would congregate in one place... and that's when it would rear up and bite!!!
 
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crane operator

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So I could mount a check valve on the primary filter base, and it would stop flow back to tank. But not probably fix our actual problem, whatever it may be.


Just going to throw another one out here. There is a pressure gauge, mounted with a hose on the secondary filter base, which should show lift pump pressure. Its obviously been added later, so they've had issues here before. What if - along the lines of Ronsii's restriction from older filter theory- we have a restriction affecting a weak lift pump?

New filters allow lift pump to operate how it should, more restriction and the pump can't pull properly, and all the pull is actually coming from the injection pump? Less restriction from a new filter- and it kind of works? Need to check that gauge while its running to see where its at. Should be 20-30psi? Can then compare that reading to when it starts acting up and see if I've got a loss of pressure. Not sure how this road leads to my leak back. :rolleyes:

Another theory, already mentioned- if the hand primer seals are out, that could easily let air into the system right at the lift pump, letting the fuel back to tank out of primary filter, not sure how the changing filters stops that though.
 

crane operator

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Mount a check valve here to stop the leakage out of primary filter? This line has been replaced, its a gates hose, so whatever fitting it is, I should be able to come up with something for it. 20191102_135127_LI.jpg
 

Delmer

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I don't think that injection pump will run pulling it's own fuel, it needs pressure.

Since you have that convenient hose for the pressure gauge, use that as a vacuum connection, with a section of clear hose, to a vacuum bottle, might take a low vacuum and lots of time to see air bubbles. Then you can see how much air is getting into the system. Once you can see the air, you can eliminate it by applying something (murphys oil soap, shampoo, grease...) to the outside of the suspect joints and seeing if the air stops. Or plug different parts of the system till the air bubbles stop. It seems pretty likely that it's sucking air at this point, and the primary filter is plugging up over three weeks. Easy to leak air under vacuum but not leak fuel under pressure.

Maybe a coarser primary filter? Or replace the primary filter only and see if that fixes it for another three weeks. Or eliminate that pressure gauge, hose and fitting.
 

funwithfuel

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40-45 psi @ idle as high as 60 full throttle no load. Full throttle full load, you should be back around 45.
The only way I see you "loading" a crane would be deadheading your outriggers and jacks. That would only be a very minor load.
Usually, if the primer pump has any grime around it, I blame that. Yours appears bone dry. That tells me it's from there back to tank.
Do you, by chance, have a fuel line that runs across to the intake manifold?
If you want to see where you are sucking air, remove the fuel return at the tank. Plug the line and cap the fitting. Remove and plug any vents. Put regulated air pressure to the tank. No more than 10 psi. The tank may bulge with higher pressure. Start low and work up. I've never needed more than 4-5 psi to show the leak. You'll see a hose or fitting get wet or spray.
 
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Ronsii

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I don't think that injection pump will run pulling it's own fuel, it needs pressure.

Since you have that convenient hose for the pressure gauge, use that as a vacuum connection, with a section of clear hose, to a vacuum bottle, might take a low vacuum and lots of time to see air bubbles. Then you can see how much air is getting into the system. Once you can see the air, you can eliminate it by applying something (murphys oil soap, shampoo, grease...) to the outside of the suspect joints and seeing if the air stops. Or plug different parts of the system till the air bubbles stop. It seems pretty likely that it's sucking air at this point, and the primary filter is plugging up over three weeks. Easy to leak air under vacuum but not leak fuel under pressure.

Maybe a coarser primary filter? Or replace the primary filter only and see if that fixes it for another three weeks. Or eliminate that pressure gauge, hose and fitting.
Exactly :) and this pretty much describes to a tee what I have done in the past to track down problems in the fuel systems on different machines.
 

Bluox

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Kinda sounds like you still have a dirty fuel tank. Next time you change filters cut your primary filter open and unwind the paper. We have a mechanical transfer pump ran with a drill motor and a vacuum gauge on it we hook to the fuel line and pump the fuel back to the tank ,finds a pick up problem right quick.
Bob
 
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funwithfuel

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I don't think that injection pump will run pulling it's own fuel, it needs pressure.

Since you have that convenient hose for the pressure gauge, use that as a vacuum connection, with a section of clear hose, to a vacuum bottle, might take a low vacuum and lots of time to see air bubbles. Then you can see how much air is getting into the system. Once you can see the air, you can eliminate it by applying something (murphys oil soap, shampoo, grease...) to the outside of the suspect joints and seeing if the air stops. Or plug different parts of the system till the air bubbles stop. It seems pretty likely that it's sucking air at this point, and the primary filter is plugging up over three weeks. Easy to leak air under vacuum but not leak fuel under pressure.

Maybe a coarser primary filter? Or replace the primary filter only and see if that fixes it for another three weeks. Or eliminate that pressure gauge, hose and fitting.
Good luck with that. Liebherr is all German metric odd stuff. Makes rigging test equipment a real challenge.
 

Delmer

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That's why I thought the fuel pressure gauge might make it easier to tap into.

I assumed the fuel system had been pressure tested already, oops. That's quicker and easier to do first.

What's with the bulge in the outlet line of the transfer pump on pic in post #13? at the top of the blue circle in post #14. Looks like a welded line, and maybe a crimp, or is it a paint run? Doesn't seem relevant to the symptoms here, but doesn't seem original on a Liebherr either?
 

funwithfuel

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That's why I thought the fuel pressure gauge might make it easier to tap into.

I assumed the fuel system had been pressure tested already, oops. That's quicker and easier to do first.

What's with the bulge in the outlet line of the transfer pump on pic in post #13? at the top of the blue circle in post #14. Looks like a welded line, and maybe a crimp, or is it a paint run? Doesn't seem relevant to the symptoms here, but doesn't seem original on a Liebherr either?
That certainly looks like a brazed line end. But its dry and on the path to the secondary. I would be concerned with injector line #1&2 . They're both wet by the clamp.
 

Truck Shop

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Mismatched threads on the Gates replacement hose? I have also had the primer hand pump on my DT466 suck air and not leak fuel.

Good point on mis matched fittings. On a Cummins small cam or big cam with a suction hose to oil pump you had have exact fittings. Cummins used three different set ups. They would thread together
but would allow air to be sucked in to oil and never show a loss of psi but with air in the oil the jakes were weak, and the two I found never leaked oil. Because the fuel hose was replaced I would
look at any thing that could have possibly been worked on first, because mistakes could have been made there leading up to this problem.
 

DMiller

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With the engine configuration leakage Out likely not gonna happen unless make it leak by pressurizing low, filters being well above tank. Any slight imperfection as to a threaded fitting, a compression angle as JIC or the variance US to Metric NPT or a slight rust spot burn thru may not leak enough running to cause a issue but enough to drain back over time.
 
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