Kniffelaufgabe: Ursachen für unrunden PD-BUK-Kaltstart? | Posts 144+

Very roughly, I would interpret it like this:
As long as the MWB13 data are not translated into actual differences in quantities, one only sees what the regulation wants to show, presumably mainly during the phase where the fluctuations increase, because no success is achieved.


In principle, and speaking in a simplified way, it's like this.
I highly doubt that this 'desired value' is accurate. As I said... These are calculated values from a control loop that hasn't yet reached its steady state.

For persistent deviations in a specific cylinder, I might be willing to pay some attention to the values, at least enough to determine a general direction. However, I would not become fixated on them under any circumstances.


...then the question remains open: why does the same specific MW of the LLRR always deviate from the norm during and immediately after startup, rather than some other random one?

When it comes to Ulf's problem, it's not always the same...

Okay, I just installed the clear tubing sections between the DFI (Direct Fuel Injection) and the engine.
During the subsequent venting process using a pre-charging tank pump, the first deviation from the theoretical expectations became apparent:

Bertil wrote:

ulf wrote: Regarding the explanation of air leaks, I have another question: Can air in the area of DiFi-ZK-PDE be discharged towards the tank by running the fuel pump for a sufficiently long time, i.e., by repeatedly turning the ignition on? DiFi tandem pump -> Yes Twin-screw pump - ZK - PDE -> No

The fuel line filled with diesel, but an air bubble several centimeters long remained trapped in the return line. The only visible reaction to the running fuel pump was a slight compression, even though I activated the pump every 30 seconds (default setting MWB 35) and the battery voltage was maintained by a charger.

The bubble only distorted when the engine was running.

Speculation: The check valve was stuck in the "closed" position within the small circuit of the fuel pump and motor, which is why the return flow to the tank was blocked.


Let's see what I can observe in the pipes in the near future...

ulf wrote:

.... The fuel line filled with diesel, but an air bubble several centimeters long remained trapped in the return line. The only visible reaction to the running fuel pump was a slight compression, even though I activated the pump every 30 seconds (default setting MWB 35) and the battery voltage was maintained by a charger. The bubble only distorted when the engine was running. ...

So, something's definitely wrong there.

With my AXR, the air actually disappears immediately during the process.

http://www.t4-wiki.de/wiki/Vorwärmventil
After that, the forced ventilation should also work even when the pressure relief valve is closed. If there's enough pressure, the pressure relief valve will open automatically.

Bertil wrote:

During the procedure with my AXR, the air actually disappears immediately.

[Curiosity ON]How do you notice that?
Ha(tte)st Du auch transparente Stücke montiert? [Curiosity OFF]

Quote:

http://www.t4-wiki.de/wiki/Vorwärmventil http://www.t4-wiki.de/wiki/Vorw%C3%A4rmventil After that, the forced ventilation should also work even when the pressure relief valve is closed. If there's enough pressure, the pressure relief valve will open forcibly.

Hmm... based on the drawing, I can't see any way for air to bypass the raised bimetallic strip (green-blue) in order to reach the return line towards the tank.

ulf wrote:

...[Curiosity ON]How do you know that? Ha(tte)st Du auch transparente Stücke montiert? [Curiosity OFF]

No ................. it was still transparently installed until recently.

It's been a long time since the friendly engine was searching for that familiar "roughness" ... back then, it was also looking for air.

I can't tell you exactly how the forced ventilation system works, but it does work... somehow. And that needs to be ensured even at low temperatures.
Otherwise, starting the VFP before the engine starts with a half-empty fuel tank would be pointless.

Bertil wrote:

ulf wrote: Did you also install transparent pieces? No ................. it was still transparently installed until recently. It's been a long time since the friendly one was looking for that rattling sound... back then, it was also about air.

Ah, an interesting side note: Was this the usual material used for aquariums and garden pumps, which becomes hardened by diesel over weeks/months?
If it's something more permanent, I would be interested in the details (source, part number, etc.) .

Quote:

I can't tell you exactly how the forced ventilation works, but it does work, at least. ..... Somehow. And that must also be ensured at low temperatures. Otherwise, starting the VFP before the engine starts with a tank that is about half empty would be pointless.

Yes... it was somehow strange. The VFP filled the clear sections to about 80%, but then nothing else happened.

ulf wrote:

... Was that the usual material used for aquariums, garden pumps, etc., that gets hardened by diesel over weeks/months? If it's something more permanent, I would be interested in the details (source, part number, etc.) .

If I knew that. The friendly person installed something. It didn't matter to me, because of the warranty...
I can only tell you that this hose has always served well during the blowing process , but it still became brittle.

You can use either polyamide tubing (PA tubing) with the appropriate inner diameter or polyethylene tubing (PE tubing). I'm not entirely sure about the temperature range for PE; many types only go up to 60°C, which might be too low.

As an assembly instruction:

If you have a piece of PA/PE tubing and you're removing something from the rubber hose, you can get a good seal by heating up some diesel on the stove (just tell your wife it's important for the country if she asks what you're doing with the diesel in the saucepan on the ceramic hob... ). Then, hold the pre-cut ends of the tubing in the hot diesel and immediately insert the piece of PE/PA pipe. If the diameter is correct, it will be a foolproof solution; put a clamp over it and you're done!

Hi there.
Before heating diesel on a stove, it's always a good idea to review our previous discussion about the flammability of fuels (keyword: "Nemesis"). We don't want the country to end up burning down afterwards.
Sure, here is the translation of the text from German to English:

"vg" translates to "very good" in English.
Herbert.

"Interesting thread... However, diesel is an oil and not inherently volatile, regardless of any additives. If we're going by that logic, all those old East German tractors and trucks where the engine block and various components are exposed to oil and diesel should be burned. Whether anything off-gasses at 40°C is irrelevant; it's certain that diesel doesn't ignite or release its gases quickly on its own, especially not at those temperatures (keyword: 55-70°C). I consider gasoline much more critical and volatile. (70°C versus -25°C!) Diesel needs a wick to ignite when cold, while gasoline ignites even without one; the fumes just catch fire."

I'm only mildly interested in theoretical values; it's not a matter of ignorance, but rather the result of my own experiences and observations, and I certainly don't consider myself to be risk-taking. And regarding the compatibility of theoretical values with good old-fashioned practice, I'm sure we've all seen things go wrong – definitely!

Caution and common sense are always necessary and should be inherent in everyone. The potential for spontaneous combustion is a matter of interpretation. Please don't fry anything with oil; it's dangerous!

And even if the diesel in the pot were to decide to burn - put the lid on and everything will be fine. Don't misunderstand me, but I have (made many attempts outside of the apartment, with boiling! Diesel at measured 160°C, for example, the gases only wanted to continue burning with an applied ignition source ). And YES, I had something fireproof from the Russian Federation nearby....

Okay, let's compare then.
Cooking oil: Flash point 230°C (it will continue to burn on its own after ignition); Ignition temperature approximately 300°C (it will spontaneously ignite at this temperature); Boiling point approximately 350°C.
That's why you can also cook and fry with cooking oil. Deep fryers have a temperature control mechanism.
Diesel: Flash point 67°C, ignition temperature 220°C, boiling point from 150°C.
In the event of a fire caused by heating a pot of diesel fuel in the kitchen, a court would likely rule that it was grossly negligent arson, especially if people were harmed, and would also consider the fact that the "cook" has a technical background.
Sure, here is the translation of the text from German to English:

"vg" translates to "very good" in English.
Herbert.

Bertil wrote:

ulf wrote: .... The fuel line filled with diesel, but an air bubble several centimeters long remained trapped in the return line. The only visible reaction to the running fuel pump was a slight compression, even though I activated the pump every 30 seconds (default setting MWB 35) and the battery voltage was maintained by a charger. The bubble only distorted when the engine was running. ... So, there's definitely something wrong with that. When I perform the AXR procedure, the air actually disappears immediately...

P.S.:
I checked the orientation of the "Knackfrosch" device: the arrow on top of the housing should point towards the tank, so it should be installed correctly.

Hello everyone!

After the temperatures here were as expected, I logged two more (unheated) cold starts on my AXC.

@-4°C:
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@-6°C:
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In the latter case, the AXC engine initially coughed only 2-3 times and then, despite continued attempts to start it, it did not restart – there was also no smoke coming from the exhaust .
At the same time, there was also a coolant (shortage) MIL error – for no apparent reason!!
Zündung aus/ein, geglüht, etwas verzögert gestartet da VCDS erst wieder synchronisiert sein mußte. DanHe ran.

What does the PDE status of "8" actually mean? These values repeatedly jump from 0.0 to "8" irregularly over a longer period of time.

Best regards from Munich!

Taken out again:

Steffen W wrote:

If one of the middle rings between the fuel inlet and outlet is leaking, the fuel pressure will drop. In this case, bubbles can form in the hot fuel. This can be observed as high negative values in MWB 23 (SSP 209 page 41). Alternatively, you can measure the fuel pressure at the test port of the tandem pump using a pressure gauge. If the pressure is too low and you clamp the return hose to the Difi during the measurement, and then the pointer on the pressure gauge moves into the target value range, then the middle PDE sealing ring is a likely culprit. By reading the MWB 23 data, you can determine which cylinder it affects.

Somehow, I also recall that with a leaky intercooler and high engine load, the diesel temperature at the sensor should be abnormally high - but I can't find any source for this right now .

If the diesel engine temperature curve from the WOT (Wide Open Throttle) data can provide any indications in that direction, what do you think of the following log data?
WOT (Wide Open Throttle) at 180 horsepower (due to tuning) in 6th gear on the highway, with an ambient temperature of 16°C, for approximately 45 seconds within a RPM range of 2700-4200.
The coolant temperature rises from 88 to 90°C, while the fuel temperature increases steadily and smoothly from 59 to 71°C.
Fuel level: almost or completely full.

I haven't had any longer World of Tanks logs stored on my hard drive yet...

Steffen W wrote:

The Sharan mentioned in the signature also starts like that.

If it's not pre-heated, and if it's very cold. It makes those noises for a few seconds... } New (slight) confusion:
Since the clear tubing was installed, I often start the engine while standing on the left side, so I can quickly observe the tubes after it starts.
Dabei starte ich wegen des Handlings meistens im Vorglüh-Schlafmützenmodus = mehrere sec nach Verlöschen der Glühanzeige, aber noch während des anschl. BereIt's a feeling of excitement and enthusiasm.

Several times, I noticed a powerful increase in speed (related to temperature) at low RPM, followed immediately by almost perfect running smoothness. Starting immediately after the glow plug indicator went out, I observed more frequent and slight misfires on average.


Conclusion:

"I'm going to check my heating system for any abnormal transition resistances."

"Maybe your other stuttering candidates will also perform better with this trick?"
Those who, unlike me, cannot see the preheating time using a control LED at the glow relay output can also estimate it by listening to the click of the dropping relay after approximately 15 seconds, and by observing the interior light becoming brighter. Shortly before the end of this time period, they have the best chance of seeing the engine start smoothly in cold conditions.

Hello everyone,
Hi Ulf!

I already tested your tip number 2 and the result is that while the engine generally starts better after repeated pre-glow cycles, the misfires still persist (although they are somewhat reduced).

Best regards from Munich!