VP44 Bleeding: Forum User Question

Hello fellow enthusiasts,

The following private message arrived for me.


Hello Marco,

.............., but I know you drive an AKN. Have you ever had to replace the diesel filter or bleed the fuel pump on your car?

If I create a vacuum at the return line of my ESP and block the return line, I should be able to draw diesel through the supply line from the fuel filter. However, the vacuum created is so strong that it pulls the lid of my sight glass inward. In my wiring diagram for the diesel system, there is neither a check valve nor any other valve (except for the Y-valve in the tank) that opens only at a higher vacuum pressure.

Have you ever had to bleed the diesel system in your vehicle? If so, what was the vacuum pressure you had to create?


Here is my answer:


Hi Manuel,

I have already replaced the diesel filter. However, bleeding the pump was not necessary in my case. I filled the fuel line from the filter to the ESP, as well as the filter itself, with diesel. It is correct, however, that the VP44 pump must be bled if it has drawn in air, or if there is a risk of it doing so when the engine is started.
Unfortunately, I can't provide you with information about the necessary vacuum pressure because I've always managed to avoid needing it so far. That reminds me: Was the ignition on during the bleeding process? If you're okay with it, I can post your question on the forum so that everyone can answer it and potentially learn something new.

Perhaps a little more background information:

'When I lightly tap the diesel filter while the engine is warm, a large number of air bubbles come through the visible section of the diesel pre-filter line. If I drive too fast, I also get error code 550, which triggers the emergency mode. If the vacuum in the pre-filter line is too high, I suspect that air is being drawn in somewhere. The diesel filter is new, and all the hose clamps are tight.'

Best regards, Manuel.

Hello everyone,

I'd like to share some interesting information about this issue.

Habe mich gestern mal auf die suche gemacht herauszufinden woher die Luft kommt. Also Schlauch vom Dieselfilter ab. Sah etwas beschädigt aus, habe ein Stück abgeschnitten Schlauch wieder ran, Filter wieder mit Diesel voll gemacht Aggregat gestartet. Nachden nach sehr kurzem lauf sehr viel Luft im Schlauch war, habe ich vorsichtshalber den Motor ausgemacht (man hört ja über VP44 und Luft nix gutes). Wollte noch mal entlüften über Rücklauf der Einspritzpumpe, kein Chance etwas durch die Einspritzpumpen zu bekommen. Also, Dieselfilter entlüftet, Schlauch zur Pumpe vollgemacht gestartet, kein Anlassen möglich. Hatte schon das Schlimmste befürtet. Nach Anruf bei meinem Freundlichen war ich um Informationen reicher-> Filter entlüften, Versuchen zu starten, ohne Starterspray wird wahrscheinlich die Batterie leergehen, hat er gesagt, kaputt gehen kann nix. Schlauch zur Pumpe noch mal gefüllt, Filter entlüftet. 10 Sekunden gestartet, das ganze 3 mal und kurz bevor die Batterie leer war sprang er geradeso an. Dann gleich mächtig Gas gegeben. KaHe pumped a lot of air in (the hose was about half full) for a good 2 minutes, but now it's working again.
The fuel injection pump blocks the flow of fuel. Up to the filter, you can easily draw diesel with your mouth without much resistance. By activating fuse 28, you can run the pump in the tank, which will fill the reservoir.

Okay, one thing I can say is that the VP44 pump will definitely not break due to air; it might only happen if you let it run dry for 5 minutes .

PS: Thanks to the kind people.

Hello everyone,

I'd like to share some interesting information about this issue.

Habe mich gestern mal auf die suche gemacht herauszufinden woher die Luft kommt. Also Schlauch vom Dieselfilter ab. Sah etwas beschädigt aus, habe ein Stück abgeschnitten Schlauch wieder ran, Filter wieder mit Diesel voll gemacht Aggregat gestartet. Nachden nach sehr kurzem lauf sehr viel Luft im Schlauch war, habe ich vorsichtshalber den Motor ausgemacht (man hört ja über VP44 und Luft nix gutes). Wollte noch mal entlüften über Rücklauf der Einspritzpumpe, kein Chance etwas durch die Einspritzpumpen zu bekommen. Also, Dieselfilter entlüftet, Schlauch zur Pumpe vollgemacht gestartet, kein Anlassen möglich. Hatte schon das Schlimmste befürtet. Nach Anruf bei meinem Freundlichen war ich um Informationen reicher-> Filter entlüften, Versuchen zu starten, ohne Starterspray wird wahrscheinlich die Batterie leergehen, hat er gesagt, kaputt gehen kann nix. Schlauch zur Pumpe noch mal gefüllt, Filter entlüftet. 10 Sekunden gestartet, das ganze 3 mal und kurz bevor die Batterie leer war sprang er geradeso an. Dann gleich mächtig Gas gegeben. KaHe pumped a lot of air in (the hose was about half full) for a good 2 minutes, but now it's working again.
The fuel injection pump blocks the flow of fuel. Up to the filter, you can easily draw diesel with your mouth without much resistance. By activating fuse 28, you can run the pump in the tank, which will fill the reservoir.

Okay, one thing I can say is that the VP44 pump will definitely not break due to air; it might only fail if you let it run dry for 5 minutes .

Best regards, Manuel.

PS: Thanks to the kind people.

So, I've also developed a venting procedure (and I do it almost every day).
For example, with the very robust 2.5 TDI engines.

Fill the filter completely with diesel.
2. Tap into the ESP return line using the diesel pump or any other pump.
3. In this case, the driver tried to pull the diesel through the pump.
One organ
4. Possibly open 2 lines leading to the injectors.

Steffarn wrote:

So, I've also developed a venting procedure (I do it almost daily). For example, with the very robust 2.5 TDI engines. Fill the filter completely with diesel. 2. Tap into the ESP return line using the diesel pump or any other pump. 3. In this case, the driver tried to pull the diesel through the pump. One organ 4- Possibly open 2 lines to the injectors.

???

Hello,

You should check the black valve at the top of the filter; there might be a hairline crack or a damaged rubber seal.

Do those little pests ever...?

Best regards,
David

Hello,

zum Saugen und Orgeln fehlt mir leider die 3. und 4. Hand

Why didn't someone tell me this sooner?
Here, in this forum, you always read that the VP44 pump shouldn't get any air in it?!
This, however, doesn't seem to be the case.

Best regards, Manuel.

Hello Manuel,

However, the specifications for the VP44 state that it should not be allowed to run dry, and in practice, the engine is even shut off before the pump runs dry. While the pump may not immediately fail, there's certainly a reason for this warning.

Hello Marco,

Yes, that makes sense. It prevents the fuel line from being completely emptied, and it allows you to start the engine normally after refueling without having to bleed the fuel system. It would be bad if the last drop of fuel was used up.

I don't recall reading in this forum that the pump piston can break.

Hi,

Since you're all having such a lovely discussion about bleeding the fuel filter:
My new Knecht KL 147 D replacement filter comes with two O-rings. I know where those go .

BUT one is black, and one is blue. Does that matter, or does it not matter which one is installed where?

There was only one filter included with mine, and no extra ones.
He was definitely black.

Enjoy your meal!

Air + VP44:

http://www.fatty-fuels.de/messages/28911.html

Hi, Jockel.

The two seals, one blue and one black, are indeed designed to be used on the diesel filter: the blue one goes on top, and the black one goes on the bottom, around the vent (the T-shaped piece) that is held in place by the metal clip.

Thank you very much!

Hello,

Since there's always something different being reported about the VP 44, I decided to do some research.
The VP44 needs to be bled in the same way that Steffarn did it.
At the beginning of the priming process, the VP44 will always be dry. Only with negative pressure in the return line and the action of the plunger pump can the VP44 be filled. The feed pump only starts when the engine is running. The problem is not the air, but the lack of lubrication, which damages the VP44. If the engine is started without priming, the VP44 will not be able to draw in any diesel because it has no pre-pump and the line would be dry. Therefore, the ESP (Electronic Stability Program) would run dry.


@Jockel
It can't be the case, because the ESP would never be able to be filled in that scenario.

Let's talk about how the V6 TDI VP44 works, for understanding.

http://www.avlditest.com/wDownloads/news/press02.pdf

Best regards, Manuel

Hello,

@Manuel V:

Thanks for the link, I'll take a look at it.

The author of the post I linked usually knows a lot about...
He also offers courses on modern injection systems.

If the engine is run without fuel, the VP44 pump will no longer be able to draw in diesel because...
> diese keine Vorförderpumpe hat und die Leitung trocken wäre. DThe ESP would therefore...
> run dry.

Based on the cross-sectional diagram you linked, it can be seen that the VP44 definitely is...
The wing-mounted fuel pump could potentially draw in diesel fuel, which is why a VP44 fuel injection pump is used.
I think I'd still like it, even if it can't be completely vented.

Could the impeller pump potentially suck in air, which could also cause...?
Do not fill VE4, VP36, or VP37 containers from a dry line.
(ehrlich gesagt, aus eigenen Versuchen kenn ichs nur von versch. VE4)

Or have I made a huge mistake somewhere, and does the FZP work differently than I thought?
in axial piston pumps?

Hi, Jockel.