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Kid347
07-30-2016, 12:59 AM
We have a 2003 sprinter and it seems that whenever the fuel tank gets below half full we get air in the fuel line coming from the fuel filter. And then it runs rough and sometime stalls and gets difficult to restart. But all seems well when the tank if full. If anyone has seen this before please forward the solution. Thank You in advance.

surlyoldbill
07-30-2016, 05:25 AM
I think I read a few years ago about a cracked hose in the tank causing that. The low pressure pump is on the front of the motor and sucks fuel through the filter to the front of the engine, and then to the high pressure pump.

Anyway, the hose is probably pretty cheap and easy to replace. Take a look through the repair manual (available on this website as a download).

sailquik
07-30-2016, 06:42 AM
surlyoldbill has it right.
Might have to buy the entire fuel line from the tank to the low pressure pump (up high on the front of the engine, driven by the camshaft as I recall)
as there are several O-rings and a clear piece of fuel line that have to withstand a significant vacuum to allow the LP pump to pull fuel
uphill from the tank.
Might get a set of the correct O-rings and clic-clamps (they handle a vacuum better as they are truly round on the inside) and replace all of them'on the existing
fuel line first.
Many have tried, many have failed, trying to preserve the vacuum integrity of that fuel line so the LP pump gets fuel as soon as the LP pump
begins turning.
Roger

Kid347
08-13-2016, 03:32 AM
well we dropped the fuel tank and vacuum tested all the lines up to the fuel filter. Sorry to say it made no difference. Still have tiny air bubbles in the plastic line from the fuel filter. I also changed the black valve that sits on top of the filter, does anyone have any other suggestions on how to resolve this issue. Again it seems the only time we have problems is when the fuel tank is below half full. Thank You in advance.

NelsonSprinter
08-13-2016, 11:25 PM
well we dropped the fuel tank and vacuum tested all the lines up to the fuel filter. Sorry to say it made no difference. Still have tiny air bubbles in the plastic line from the fuel filter. I also changed the black valve that sits on top of the filter, does anyone have any other suggestions on how to resolve this issue. Again it seems the only time we have problems is when the fuel tank is below half full. Thank You in advance.

It may be just a coincidence, and the air is sucked in from the fuel filter connections. Lube all O-rings with heavy oil and do not tighten water drain valve or try a fuel filter without a water sensor on bottom in my link

surlyoldbill
08-14-2016, 01:14 AM
An over-tightened water drain valve on the fuel filter is a notorious source of leaks. It deforms the round side of the filter if tightened too much, and the gasket/o-ring cannot seal if not pressed evenly.

Maybe the half full tank is allowing fuel to drain back to the tank through the return lines more easily. Air intrusion allows the fuel to travel to the lowest point.

Aqua Puttana
08-14-2016, 11:57 PM
During starting a full fuel tank is easier for the pump to suck from than an empty one. You may have some odd marginal component which is ok until the going gets tougher.

But...
you said...

... below half full we get air in the fuel line coming from the fuel filter. And then it runs rough and sometime stalls and gets difficult to restart. ...
Do you mean that any time the engine is running and fuel level falls below 1/2 full the engine begins to run rough?

If yes, it almost must be a pickup system assembly issue within the tank.

You don't have some other diesel appliance tapped off the fuel system by any chance? That might add issues.

There have been those who have installed an in-line electric fuel pump between the tank and the fuel filter as a response to air leaks. That is treating the symptom, not a cure.

vic

Kid347
08-16-2016, 03:48 AM
I will try the few suggestions that you nice members have suggested. I am thinking of just changing the fuel filter just to eliminate it from the equation. I am at a 1/4 tank now and it has starter every time without stalling. But I do see tinny air bubbles in the clear line coming from the filter to the low pressure pump. I will report back my findings, Thank you all very much.

Zundfolge
08-16-2016, 05:45 AM
That was going to be my suggestion. In my years of experiences with diesels it's basically #1 on the top of the fuel system troubleshooting list, almost no matter what the symptom. Can't count how may times it's resolved what I thought was a much bigger issue. Good luck!

Aqua Puttana
08-16-2016, 07:45 AM
Running and starting now with a 1/4 tank doesn't sound like a pickup assembly problem.

... I am thinking of just changing the fuel filter just to eliminate it from the equation.
...
If you find traditional worm drive hose clamps on the fuel lines replace them. The distortion caused by the irregular shape of the worm drive tension block can allow air leaks. Use proper fuel injection type hose clamps which completely encircle the hose smoothly.

As was mentioned, don't over-tighten the Water In Fuel WIF sensor. The WIF uses an O-ring seal which needs to remain un-distorted.

vic

Kid347
08-30-2016, 10:55 PM
Happy to report that our fuel problem is fixed. After changing filters, valve on filter, fuel lines it was the sending unit. No more air in line and she runs great. Thanks for all the support.