Diesel leaking from the return line (AEL) after ESD replacement

Hello everyone,

It's about an older Audi A6 2.5 TDI, 5-cylinder, AEL engine, 140 horsepower.

I have installed a set of ESD components, which was recently refurbished by Bosch Bieberach, in my classic Audi. (No modifications or tuning).
The return lines were replaced about 3 months ago, and the car has been driven without any problems since then, even with the old ESD (and the new return lines).

Now, the refurbished ESDs have been installed today, and the mouse is no longer needed.
The engine is running (at least) in idle, but...

Diesel fuel is being pumped out of the last return line, which connects the last electrostatic precipitator (ESP) to the main scrubber water (MSW) system.

If I redirect the aforementioned return line from the last electronic fuel injector (ESD) to a bottle, no diesel comes out, either when the engine is idling or when I slightly press the accelerator. This shouldn't be possible with the old system, because with the old system, diesel flows from the fuel supply module (MSW) towards the return lines of the ESDs with good pressure, which is essentially the wrong direction.
I have already bypassed the Diesel Filter Water Separator.

Does anyone have any idea what might be causing this?
With the old nozzles, that problem didn't exist.

Unfortunately, I am not familiar with the structure of the old ESD (Electronic Service Document).
Could it be that there's a valve or similar component in the ESD (Electronic Stability Device) that normally diverts excess fuel towards the return lines, and that this valve is installed incorrectly or in the wrong position, or that the new components were installed incorrectly?

Do you have any ideas?
Bosch Bieberach will be going on a 4-week vacation soon, and of course, they haven't responded to my email.

(Search function included.) I used Google Translate, but I couldn't find anything.


Thank you for your efforts, and best regards.
Wool.

Please take a picture and label what you mean.

It's essentially a VP37, like the one used in the AFN, but with one more cylinder.

Hey Rüdi,

Thank you for your reply.
Here are the photos, including the ones you requested. Attempt at explanation.

In the photo, with all the components visible, the ESP (Electronic Stability Program) is located in the upper right corner.
Immediately to the left of that is the cylinder where the smoke is coming out... (Number 5 is still running...)

In the photo, where mainly only the MSW (presumably a type of cable) is visible, it refers to the nylon-reinforced cable that is labeled by the manufacturer.
Here's where the problem can best be described...

Between the labeled return hose (left in the image) and the yellow-marked screw from the MSW, you can see a small red dot. It's a coincidence, but it fits.
And it's also about the connection that this hose makes.
In the upper left corner, you can see nozzle number 5. In the lower right corner of the image, there is the connection point for the return hose to the MSW (presumably a machine or system).
Not a single drop of diesel is coming out of this labeled return hose while the engine is running.
Even if I were to increase the speed to, for example, 1500...2000... RPM.

MmN should be the point where the excess diesel that isn't burned by the ESD (Exhaust Smoke Device) exits.

But unfortunately, no...

Currently, diesel fuel is being forced out of the MSW connection, specifically at the point where the blue connectors are visible, and flowing towards the ESD, which is in the opposite direction of the return lines.

I hope that was understandable.
Just send me a private message, and I'll reply with my phone number so you can call me back, preferably anonymously.

I just don't know how I can better describe the problem...

I'm really sorry...

Best regards,
Wool.

The return line of the ESP is either kinked or incorrectly connected...

It's designed so that more diesel fuel is injected into the VP37 than is actually needed, except perhaps when running at full throttle and demanding maximum power.

And the excess fuel flows back into the tank, bypassing the Knsckfrosch (which is supposedly responsible for filtering the fuel).

It's perfectly normal for there to be a strong flow when the engine is running; the urine from the nozzles is just an additional factor.

What I may have missed, does the engine run normally in all situations?

Hi,

wolle wrote:

Could it be that there is a valve or similar component in the ESD

that normally diverts excess fuel to the return lines, and that this was installed incorrectly or in the wrong position, or that the new components were installed incorrectly?
No, the ESD's leakage oil is being forced out from the nozzle body, bypassing the valve, and going directly to the leakage oil line connection.

I'm not very familiar with the field of VEPs, but the following thought occurred to me:

Was the hollow screw removed from the MSW?
Could it be that the hollow screw on the MSW ring connector has a calibration/throttling hole or a ball valve (which maintains a certain pressure inside the pump) and that this was accidentally replaced with an incorrect (open) hollow screw?

Best regards, Richard.

Hi,
I don't understand what the problem is.
Is the return line leaking, or when you open the return line, does a large amount (everything) come from the main water supply (MSW) and very little (nothing) come from the nozzles?
hg
Herbert.

The return line is secured with a nut, so there's nothing to swap around.

Rüdi wrote:

The return line is secured with a nut, so you can't swap anything there.

No idea, I've never had a car like this before. I see a hollow screw in the picture of the ESP.
If, however, a "Knackfrosch" (a type of device) is installed in the Difi system, it will have a connection to the ESP (Electronic Stability Program) and one to the fuel tank.

When it's cold, the ESP's return line is connected to the DiFi, and the return line to the tank is closed.
If someone now swaps the connections on the "Knackfrosch" device, the return flow from the ESP to the DiFi is blocked... that's my theory.

Hi.

The hollow screw is located upstream of the VP37.

There's definitely nothing to confuse here.

I would temporarily bypass the entire diesel filter so that fuel can flow directly from the tank to the fuel pump and back.

Hi everyone,
Thank you very much for your efforts and the answers.

I definitely didn't misinterpret or misunderstand anything. I can guarantee that.

Herbert got lucky.
"No drips are coming from the return lines (from the direction of the ESD), but everything is coming from the hollow screw of the MSW and is also pushing in the direction of the ESD."
I have already installed the approximately 6-month-old "Knackfrosch" (likely a specific type of component) and it is correctly positioned. Especially since I didn't have to deal with that myself.

I just temporarily blocked the connection from the return line on the MSW towards the ESD, and lo and behold, everything is okay.
However, I don't want to know what kind of pressure the diesel is now being forced out of the tank with...

I cannot answer how the "problem" behaves during operation, because I didn't want to run it unnecessarily with the heavily leaking hose.
But he will probably drive normally. I'll test that later.

What's confusing me is that the problem with the nozzle replacement occurred.
I probably searched in the wrong direction.

I have another hollow screw lying around, but I need to find it first. Let's see if this works.
Otherwise, a check valve will be installed in the line between the last ESD (Emergency Shutdown Device) and the MSW (Main Switching Device), and then things should be quiet...

Best regards,
Wool.

Again, it's perfectly normal for diesel fuel to flow back into the tank, especially when the engine is idling.

Hey Rüdi,
Yes, that's quite clear. Don't worry .

However, it's certainly not normal for the pressure to be high enough to force the diesel "backwards" out of the oil return line, especially since the lines are almost new.
But I'm going to replace the shielded cable with a thicker, unshielded cable. Perhaps it's sitting too tightly on the connector nipple and that's what's making it seal.

"These hoses are always a bit tricky. I use fabric hoses that I buy in bulk from a specialist shop. They're so tight that I can only get them on if I first slide the ends over a pointed plier that's been dipped in grease, which slightly expands them."

They are practically a few tenths of a millimeter smaller than the diameter of the nipples where they need to be attached.

Hey Rüdi, that must be a tight fit.
I just happened to have a clear plastic tube from aquarium equipment on hand, so I used that. I don't have an aquarium, but the tubes are still great.
The hose is really tight on the nozzle.
However, the diesel engine is making a noise at the last exhaust manifold.
Then I bent the hose, and everything was fine.
There's a lot of pressure on the line right now...

When I turn off the engine, the diesel fuel from the oil drain line is sucked towards the MSW (Motor Support Unit) and, consequently, towards the fuel tank, even though the tank is open and should not have any vacuum (due to the tank ventilation system).

I once searched for the hollow screw from MSW, but I simply can't find it.
Perhaps Richard is right, and my set screw is either loose or defective.

I will check everything in the coming days and look for a replacement hollow screw.
(So, if anyone has a complete version for sale...) Feel free to contact me via private message.

More information will follow when I have something new to share.

Thank you all!

According to 7zap, there's a hollow screw with a backflow restrictor inside, but in practice, it's a threaded stud with a nut that's closed on one side.

"That's the same problem I'm having with my AFN, but there must be a return restrictor somewhere..."

Unfortunately, both of my AFNs are currently in storage; I would have liked to take a look at them.


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