Fuel system bleeding - Audi A4 3.0 TDI BKN (Solution)

Hello everyone,

I just replaced the cylinder head of the left bank because an injector was faulty, and secretly dug a hole all the way to the coolant channel.

The new (used) cylinder head is on, including the head gasket and exhaust manifold gasket, etc. all new, (initially) a new injector, everything reassembled, injector values entered into the ECU via VCDS, fault memory cleared.
Until then, everything is fine.
I'm just unable to get the fuel system to bleed.
I have already read several instructions and tried it several times, but I am unable to get the air out, and therefore I am not getting any pressure on the rail.

**To the Procedure:**

Fuel filter pre-filled, HD pump inlet disconnected and connected to a bucket with a hose. Then, after performing the fuel pump diagnosis, run the fuel pump until no more air bubbles were visible.
Attach the suction hose loosely to the HD pump and press out any remaining air from the connection, then tighten the screw.

That's all, folks.

Then, following the instructions, disconnect the fuel regulator valve and let the starter run for about 10 seconds.
Suddenly, I had air in the feed line of the HD pump.

I'm just assuming that this is the air coming from the return of the pump, which goes directly back into the diesel filter through the bimetallic valve (bimetallic valve? ).
Am I right?

If so, how do I get the air out of it?

"There must be some way, Audi certainly didn't assemble the car by submerging it in diesel."

By the way, the tank is about half full.

Does anyone have any ideas?

Thank you in advance.

Greetings,
Micha

Possibly. Return and forward swapped?
Nothing damaged or broken?

Does diesel fuel directly enter the injectors?
Potentially, try loosening the fuel lines to the injectors while starting the engine to see if diesel starts to flow.

Hello Auto Service,

"Incoming and outgoing are not mixed up. I just took another photo and compared it to the condition before the renovation."

Nothing gets to the injectors, and I've already loosened the connection.

How long would it take the HD pump to completely fill the empty rails?

Hey,

Okay, the process is underway.
I simply replaced the temperature valve with two connecting pieces, as a precaution, and also bled the diesel filter again. After about 10 seconds, it started working again .

Now the exciting question: Does it absolutely have to go back in?

Greetings,
Micha

Thank you for the feedback

Quote:

Now the exciting question: Does this thing absolutely have to go back in?

Install... is not just casually installed, but is also a great solution in times of "cheap is good".

You just have to make sure you're quick, so that the system doesn't run out again, or that as little air as possible gets into the system.

Ok, I'll reassemble the part.


However, a test drive should not be a problem, right?

I don't think so, but I also don't see any point in reinstalling it immediately.

My idea was to increase the diesel temperature above 35°C, so that the "Knackfrosch" (presumably a component related to diesel fuel) moves towards the tank, and the air that I re-introduce doesn't directly enter the diesel filter.

... don't make it a state issue if the system is okay, then it will resolve itself.
a) Check if everything is properly connected and not accidentally sucked in through the return flow, or if a seal has been forgotten, etc.
b) Rail: To release a retaining nut from an injector and simultaneously attempt to bleed. Fill the diesel filter before installation.

Best regards, Rainer

Good evening!

Okay, the project is back on track, with Knackfrosch.
Nice and warm, put the frog in, gave it a quick squeeze and it started working again.
Then thoroughly flush the cooling system again and refill it with fresh G12+ mixture.

In the next 262,000...

Thank you for the feedback