Blocked Fuel Tank Return: Causes and Solutions.

Hi, it's me again...

After successfully completing the all-inclusive vacation in Italy, which involved driving 2500 km without any problems, I encountered the familiar diesel smell again at the last rest stop... The first noticeable issue: the blind plug on the last injector, where there is no oil return line attached, is missing . Okay, I improvised and it worked for now. But now, back home, I've investigated the problem, and the real cause lies in the return flow to the tank: it's somehow blocked, and now the fuel isn't being pumped back into the tank, but is instead coming out wherever it encounters the least resistance. When I disconnected the oil return lines from the pump and briefly started the engine, a real gush came out, whereas normally only a few drops should be going IN .
"If I disconnect everything and only have that short piece of tubing connected to the tube leading to the pre-heating valve, and then I blow into it, I really have to puff my cheeks out quite a bit... Is there a valve under the tank that could be blocking it? I honestly can't imagine that the tube itself would suddenly develop a kink or something during operation. Also, I've checked the tube as much as I can - I haven't noticed anything unusual."

Any ideas?

What kind of car?

Sure, no problem:

I eventually built a signature.

Tubes, hoses, blowing ???

So, you've already ruled out the bi-metal valve for pre-warming (the part on the diesel filter) because you can blow air through the hose in the correct direction *behind* the valve, right?

Is the valve definitely open and allowing flow?

Disconnect the return line from the ESP (electric submersible pump) and blow it through.

I believe there's not much groundbreaking technology left in tanks anymore.

m;

Hello,
Have you ever inspected the fuel sender? Is it accessible from the interior (rear seat)? I once had a case with a friend who often transports bulky items; in his Passat, a charging cable had gotten wedged in the fuel tank's pipe bend. The fuel gauge was already inaccurate. Always open the fuel cap before blowing anything into the tank!

Best regards, Robert.