Air in fuel lines - Ive tried everything.


New member
So I read the threads here and other places and the fuel filter seems to be the least desireable one available. My issue like others is that I have a TON of air in the line and there's so much that the lines turn white due to all the bubbles, when the engine is running. I took the filter out and check the water sensor, then used my fingers to plug the out port and the return port, then put a hand vacuum pump on the inlet. I was able to draw and hold a vacuum so that told me that the bleed valve and the water sensor weren't leaking or letting air in. I then put the outlet nylon line on and plugged the return line, drew a vacuum and it held. i then put the return line on with the outlet line on, drew a vacuum through the inlet and it held. so that all seemed good. I also put a clear line between the inlet black hose and the filter so I could see if air was in the line and guess what, none, clear without air. I ran the van and saw NO AIR in the inlet line but fuck me if the outlet wasn't a diesel latte, so, much, foam. At this point I just want to put an inline filter between the tank and LP pump and put a union between the return and tank and not put that fuel back into a filter so will that work or is there some magic I'm not aware of? What's the anatomy of that filter, is it putting the return fuel on the same side of the feed line in the filter and then going into the LP? do we REALLY need return to go to that filter? I don't have time to wait for parts to arrive and EuroSD doesn't have the non water sensor filter nor do they have the plastic T for the return and ebay looks like the only other place I can get those parts but I can't wait until next thursday since it's a holiday. I'm willing to bet air is coming in from the return line somewhere like one of those stupid ass places it's connected to under the plenum, oh and it's an om612 so I got the nightmare plenum.

The reason I found the diesel foam (air in the line) is because I have 3 p codes and low pressure pre delivery is one of them and I'm willing to bet it's because of the air in the line.

Anyway, thanks in advance and I really did try to find an answer in old posts.


'02 140 Hi BlueBlk Pass
Just guesses: When was the last time you replaced the O-rings? Are the Voss connectors latching?


Active member
As a 612 owner I share your frustration and hatred of the plenum. Your idea to skip the filter makes sense on an emergency basis, IMHO the fuel filter is there to protect the injector nozzles and warm/cool fuel in extreme temperature situations. You will need to match the volume, an inline filter might slow down flow.

If your idea works please share.



New member
So as is tradition, I think i found the problem RIGHT after I posted this. I dug deep and found someone testing the fuel return valve and they found that it wasn't working properly. It wasn't closing from the tank return line which let air into the filter. I'm bypassing the filter to see if it fixes my problem and gets rid of my codes.

Sprinter Snail

Active member
All diesel engine fuel return line should be below fuel level for preventing fuel drain from system. Both lines pick up and return close r=to the fuel tank bottom. Should be no air in return line after system was purged, fuel return line inside the tank is not damaged. Do you have long cranking time after van was sitting couple days?

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