Got a interesting one, at least I'm still grasping at straws. 2000 liebherr crane, liebherr engine, v-6 twin turbo, electronic throttle on a mechanical injection pump. 2 fuel filters, primary and secondary. I've owned this rig for about 8 months now. Its got something goofy. New fuel filters, after about 3 weeks of running, will drain back to tank after sitting for 1/2 hour or so. So if it sits, its got enough fuel to start the engine, run for about 15-20 seconds, then it dies. Crank on it for about 20 seconds, it will pick up, and run fine. It starts doing this after the filters have been in for about 3 weeks or so. If you change fuel filters, the problem goes away, and it will start right up, and not die. After the filters have been in for a while (3-4 weeks- variable), it will start dying right after starting, like there's a fuel line drawing air, or a check valve stuck, allowing the fuel to return to tank/ siphon from one of the filters. But if you change filters, the problem goes away. At first the dying will only happen if it sits overnight, getting progressively worse to losing prime within a half hour. Have checked all the fuel lines for tightness. Probably need to pressurize the fuel tank a little and check for bubbles. But I can't see how changing fuel filters, would make a line leak go away. Just for additional info, the crane had set still for a year and a half before I bought it, had nasty old fuel in it, and I flushed, cleaned tank, and bio treated a bunch to get things cleaned out. I don't mind replacing filters, because it seems to cure it for a while each time, I'm just having trouble figuring out how changing filters could be curing my losing prime problem. Ideas?
Could the filters be shaking loose.... like a cummins oil filter does then it starts leaking a month after it was put on
Is there a check valve somewhere in the supply line to prevent back-flow that may be defective ?
Some filters have anti drain back valves (Like a flap check valve) . Do your filters have this? If so could they be degrading from the fuel (ethenol) over time?
I like grasping at straws sometimes Have you cut any of the old filters apart to check for slime? How about taking the filter off and putting it right back on to see what happens. Any screen or strainer in the tank? or a banjo bolt screen in a pump inlet? Maybe they backflush just enough when you change the filter, then plug again slowly, and cause a fuel vacuum that sucks air in through some tiny crack.
Does it have a piston primer pump on the lift pump or filter head? I have been duped by those things more than once. What filter is getting sucked dry? Primary or secondary, or both. Maybe spin the filters down first to see where you're at. That would help narrow your field of view.
This is very similar to a common Cummins losing prime problem. I lose prime overnight on my M11. There could be a one way check valve on the fuel line that is stuck open but on Cummins a simple fix is try a different brand of fuel filter that doesn't drain back. Baldwin actually makes a special filter to help with the problem on Cummins engines (BF1259 with standpipe to prevent drain back). I took the check valve out and it was stuck open so I cleaned it. However that didn't fix the problem. I put the Baldwin filter on and I think it partly helps but doesn't completely solve the problem. I think it just has less fuel drain back when sitting overnight. What I found does work is to start the engine and bring the idle up to about 1100 RPM and hold it there for about 30 seconds until the engine starts to struggle from lack of fuel. Usually that is enough to pull fresh fuel but sometimes I give it full throttle when it starts to stutter and after a few seconds is running normal. Then I can let idle at the normal 650 RPM or so to build air pressure. After that it is good all day to shut off and start back up. Giving it a little more throttle after starting seemed easier than trying to track down the tiniest of air leaks somewhere in the fuel system. It was more of a problem before I replaced the batteries. Would start initially and die 30 seconds later. Then the batteries were too low to crank it for 20 seconds to get fuel. Below is a thread on the problem. Does it only happen with a low fuel tank or does it do it when full as well? Have read the return hose might not be low enough in the tank and picks up air. HeavyEquipmentForums
Are you running aftermarket filters? Have you tried a different brand?
X2 on the Baldwin Filter.. & regardless of what fuel system u have.. they have a check valve somewhere.. either an overflow valve or check vlvs in the supply pump..
I'm pointing at the supply pump. I have had issues similar due to the fact that the check valve don't always seal tight.
Ok, here's one that goes with this problem Have a outside customer with a T800 N14 1996 used as a septic pumper. He has owned it since 2000 starting about 2002 after a service it started having a loss of prime issue. A long bodied fuel filter was installed Napa/Wix brand he installed it. Then after 4 days it had starting issues then it got down to 1 hour and a loss of prime. A short bodied filter BF957 was installed and no more issues. Then on the next service a BF1259 was installed, problem started all over again. This time a Napa short 3109 was installed problem went away. This truck/engine does not like long bodied filters, runs fine all year long using the standard short filter of any brand. It runs so I don't worry about.
I had a situation on a JD where a bowl was installed on the bottom of the primary filter and an oring was inadvertently omitted. Exhibited the same symptoms and didn’t leak externally. Took a while to sort that one.
Sorry guys, been a little busy, thanks for all the replies so far. Here's some pictures and some more info. Big filter is a Wix 33341, small filter is a Wix 33472. We use Wix because my parts supply choices here are oreillys, oreillys or oreillys, who carry a house brand or wix. Anyways, when we changed the filter last time, the big filter was the partially empty one. It looks to me like the fuel comes from tank, to the big filter. Then it goes to what I'm guessing is a small lift pump driven off the injector pump, which also has a hand primer piston pump. That pushes the fuel to the secondary filter, which sends it to the injection pump.
Fuel filters are dry, and I've had that happen to me on a oil filter also. I've also had fuel filters loose, and I've always found that by fuel dripping. Doesn't seem to be a check valve on either filter head, I don't know where it would be located, without taking all the fittings apart, I may be making more air leaks that way than I'm fixing. So I'm guessing that this is the lift pump, and its driven off the injection pump. The black handle is the primer pump. I'm thinking that if there is a check valve in the system, its in one side or the other of this?
I would closely check the line from tank to primary filter. May have a crack in it. Check the fitting it feeds from, check for cracks. Sounds nasty, but see if you can siphon fuel from that fitting. You're trying to see if there's crap in the tank or if the standpipe is cracked. The lift pump primer looks bone dry. I would not be too concerned with that, yet.
The fitting on the LEFT.. the entire fitting IS the check valve.. There is another inside the supply pump but u have to take it off & apart to get to it.. I would pressurize the system & have someone w/ a spray bottle w/ soapy water spraying down the lines. Have u primed the system w/ the hand primer before u start the engine.?? does it pick-up & run?
The fact that it starts and runs then starves says that the problem is from the lift pump back to tank, sucking air, which allows siphon to break.
TPG beat me to it.
I've not tried hand priming before trying to start the crane, when its doing its dying thing. We swapped fuel filters last week again, because it was dying, so right now it runs fine. In another three weeks, if things go like they have been, we'll be at the point where we can start trouble shooting again. Part of the issue, is if you have counterweights on, and the crane is swung to the rear, or the boom is in the rest (travel mode), its not easy to get at the primer pump or either of the filters. You can do it, but its a job. Can't just pop the hood and give it a couple pumps on the primer. All the fittings and lines around the filters are dry. I have totally drained and cleaned the tank when we got it, and everything looked good in there. Pressurizing is probably the next step, but the crane has been working and running, its just one of those things I need to get sorted out. I kind of like the gradual build up theory, but I'm not sure how it fits with this problem. I had a check valve totally plug with slime like that once. That crane, you could drive about 20 minutes, the slime would pack the check valve, and kill the engine. Twenty minutes later the slime had fallen back into the tank, and you could restart the crane. Then you had another 20- 30 minutes before it picked up all the slime again. If I have a leaking line or fitting, I don't see how changing filters helps it. If I have a check valve not shutting, I don't see how changing the filters helps that issue either. Filters are tight when we go to change them, and dry.
I once had a fuel cap tether chain get pulled all the way up the standpipe to the first elbow. When you'd take the filter off, the chain would stretch out in the standpipe, fire it up and it would gradually get bunched up and starve it for fuel. That was on a 90s L8000 with an N14. Lost a lot of hair on that job.
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 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. 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.
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????
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?
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.
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!!!
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. 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.
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.
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.
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.
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.
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
Good luck with that. Liebherr is all German metric odd stuff. Makes rigging test equipment a real challenge.
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.
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.
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.