Fuel filter issues?

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.

https://www.heavyequipmentforums.co...ctually-found-the-problem-and-fixed-it.64145/

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.

Ronsii said:

Could the filters be shaking loose.... like a cummins oil filter does then it starts leaking a month after it was put on

Click to expand...

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.

Tinkerer said:

Is there a check valve somewhere in the supply line to prevent back-flow that may be defective ?

Click to expand...

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.