TDI springt schlecht an nach Standzeit | Posts 16+

I suspect that while the engine is running, some diesel fuel leaks out (see tissue), but when the engine is off, the diesel fuel drains back and slowly draws air into the system through the crack.
The extent to which the pump can run dry likely depends on the piping configuration and the channels within the pump.

That's exactly right! And there's no issue with 'stuck' vanes. If diesel fuel is present in the system, the wax components will dissolve and flow through it. Even if only oil were in the pump, absolutely no sticking would occur after such a short time (less than 1 day). But never mind. We have a spare pump lying around that ran for 'forever and three days' on 100% oil. It wasn't stored away or anything like that. After about 3/4 of a year of being unused, it was installed and is working fine. So much for the idea of sticking!

@morti
Your leaking oil lines are likely the cause! At this point, you should probably replace all the oil lines at once. The hot oil makes them brittle over time. This is especially true for products from your mentioned supplier. We've had similar experiences before!

Hello Lappen and Ulf,
This morning, it started up pretty well; I think we've found the problem!
It was just a tiny, annoying hole in the blind plug of the oil feed lines.
I didn't replace that one when I was changing the injector holder combinations; it was the only part I left untouched. I did, however, replace the oil return lines with new ones.
The tricky thing was that you couldn't see the air being drawn through the hole in the transparent fuel lines. It probably accumulated in the ESP (Electronic Stability Program) and was then directly forced into the lines leading to the injectors. Or is there another possible explanation?
Thank you very much for your help so far!

Best regards.
Morti.

@morti

Then bring on the case of beer!

morti850tdi wrote:

The tricky thing about it was that you couldn't see the air that was being drawn through the hole in the transparent fuel lines. It probably accumulated in the ESP (Electronic Stability Program) and was then directly pumped into the lines leading to the injectors. Or is there another explanation possible?

Hmm, if there's air in the pump, it should be vented through the return line as soon as possible.
If you have a clear section in the return line, you should see bubbles when the organ is running – unless only air is being pushed through. In that case, the clear section filled with air will appear different due to light refraction compared to when it's filled with fuel.
Can you confirm any of that based on your observations?

I'm considering incorporating your experience into one of the technical articles: "Starting problems become more pronounced with longer periods of inactivity."

Hmm, if there's air in the pump, it should be vented through the return line as soon as possible.
If there's a clear section in the return line, you should see bubbles when the organ is running – unless only air is being pushed through. In that case, the clear section filled with air will look different due to light refraction compared to when it's filled with fuel.
Can you confirm any of that based on your observations?

No, that definitely wasn't the case. After having to prime it for a long time, there were no bubbles, foam, or anything else visible in the clear piece that would indicate the presence of air. That's also what made the search so difficult.
If there's only air left in the hose, the experienced eye (which I now have ) can also see that. But in such a case (e.g., when I recently replaced the small diesel filter, see above), it sometimes won't start at all until you bleed the air out with a bicycle pump.

This morning, it started up quite well again, but not perfectly yet.
However, it seems that the end cap is not yet 100% sealed.
After a 450km drive yesterday, I found fuel traces again on a test cloth wrapped around the filler cap. However, it was much, much less than before I wrapped the cap with duct tape. Tomorrow, I'll get a new filler cap, and hopefully that will solve the problem.

'@Lappen: The case of beer is ready, you have to pick it up here in Hanover. Which brand?'

@Ulf

If you want to include this in a technical article, it's only half the truth, or rather, it represents only a small fraction of all possible scenarios... Further approaches are outlined in my previous explanations. However, I don't consider it necessary or helpful because, in 95% of cases, the problem is related to air pressure, while the rest involves things like broken springs, etc. Also, we're dealing with a special case here. A KGR (likely referring to a specific type of component) is installed, which introduces additional problems. Such issues are usually only clarified through direct communication and not in general technical articles!

@morti

If you're looking for a blind plug, don't use the original part from Auh Weh! They are known for being prone to defects. If you want to do it properly, you can use a piece of oil return line inserted into the return flow instead of attaching that blind plug to the first injector. You can find instructions for this at Monopoel. Also, your bicycle pump might be causing problems! I've read about various issues with them in online forums.

lappen wrote:

because in 95% of cases, air is the problem

.
...as is apparently the case here, and it enters the system through leaking oil lines.
This could potentially affect practically every VW TDI vehicle sooner or later.

Or can the pumps, without a modification to the fuel system, not run as dry as those from Morti?
(I practically have no knowledge of specialized systems for wood processing.)

...as is apparently the case here, and it enters the system through leaking oil lines.
This could potentially affect practically every VW TDI vehicle sooner or later.

Or can the pumps, without a modification to the fuel system, not run as dry as those from Morti?
(I practically have no knowledge of specialized systems for ).

'Ulf, in this case, we're dealing with some specific characteristics of the wood gasifier operation and the necessary/carried-out modifications for it. The main problem with these modifications is both the compression ratio (KGR) and the system for preheating the wood gas. Especially the latter is a major issue when there's air in the system. If that gets in, it takes a very long time to get rid of it, and if you're unlucky, the thing might not even start at all. A possible solution could be a quick vent valve. This is practiced in some circles, but it's also quite controversial. Another solution for such scenarios would be a pump for venting air. That's why I asked about it earlier. Another alternative, which I personally prefer and use myself when I'm traveling with a wood gasifier, is to open the compression ratio (KGR). This restores the original state, and any potential air will go towards the tank. Also, there's the issue of the hot wood gas. 75 degrees Celsius is mandatory before the ESP (exhaust gas purifier). This causes the lines to become porous much faster than with diesel. Another factor. And so one thing leads to another, and with this type of operation, you can no longer assume normal operating conditions and directly compare them.'

lappen wrote:

The main problem with these conversions is, on the one hand, the KGR (Kondensgasrückführung - condensation gas recirculation) and, on the other hand, the mechanism for preheating the combustion chamber. The former, in particular, is the primary cause of problems when there is air in the system.

Okay... I think KGR stands for "short-circuit return."

Sure! / Yep! / Absolutely!

Yes, the presence of a catalytic converter prevents any air trapped in the fuel system from being vented back into the tank through the return line.
The disadvantage is addressed by using a venting valve, which typically only opens briefly during the ignition process. At that moment, the return flow to the fuel tank is opened, and accumulated air (since the valve is located at the highest point) is released.
However, if there is too much air in the system (e.g., after changing the fuel filter), this device may not be sufficient. But you can manually set the bleed valve to 12V, which will continuously open the tank return line until no more air bubbles are visible.

After the plug wrapped in duct tape had lasted for about 2 weeks, the engine started poorly again. It was probably not a permanent solution .
At my local Audi dealership, they didn't have the correct plug in stock, so I tried using a small piece of leak-off pipe that was sealed with a screw.
Although no fuel leaked out, it still started poorly. That means there was air getting into the system somewhere near that screw!
I then bent a new section of leak oil line twice and secured it with two cable ties.
Now it's quiet, and it starts up better again!