Kniffelaufgabe: Ursachen für unrunden PD-BUK-Kaltstart? | Posts 96+

Because it fits better here than...
Okay, I'm ready. Please provide the German text you want me to translate into English.
to delve deeper into:

DieselBär wrote:

So far, no search for air leaks has been conducted. When I have some time, I promised Steffen_W that I would measure the pressure of the tandem pump. He suspects that this is the cause... . . . He may be referring to a built-in PDE (Positive Displacement Element) seat, from which combustion gases might escape, especially when the engine is cold.

It sounds plausible at first glance, but it probably doesn't quite fit in my case.

Because the longer I observe this behavior, the clearer it becomes that it is encouraged by...

1. low start temperatures AND

2. long operating times.

After several days of inactivity, it occasionally spits out a small amount of liquid, even with logged coolant temperatures that wouldn't normally cause any issues, such as those observed after a night.
If combustion pressure (temperature-dependent) were to be introduced into the diesel cycle, then, in my opinion, the dwell time would have to be completely irrelevant beforehand, and there would only be a correlation with the temperature of the engine block at startup.

I also find it unlikely that diesel is dripping into the cylinder when the engine is off, because the noticeable light blue smoke only appears when it's misfiring – usually a few seconds after starting (plus the time it takes to travel through the exhaust).
The smoke from a diesel puddle in the cylinder would likely start coming out with the first normal puffs of soot from the exhaust... ?


How does it work with your T5?

Hi Ulf!

As mentioned before, I would like to first follow Steffen_W's tip and then continue with further philosophical discussion .

Regarding my T5 van, I have to say that it rarely stays in one place for more than a day. It's meant to be a work vehicle, although it can sometimes cause trouble.
As far as I could observe, the amount of time it sits unused seems to have little effect. Sometimes it starts much worse if it's been cooled down overnight, compared to when it sits for almost two days straight.

The stupid device always spits out errors especially when nothing is plugged into the OBD port - well, that's obvious.
Recently, I got a laptop and a webcam, and I wanted to recreate one of Ulf's videos, but it ended up being just a short burst, and you could barely see anything coming out of the exhaust.
I'll wait to see how it performs in temperatures around freezing, try preheating it multiple times, and then I'll report back – unless I manage to get my hands on a tandem pump pressure gauge beforehand.

Best regards from Munich!

P.S. ...still waiting for LOG 13/18/23 from you ("the 5th").

DieselBär30x wrote:

PS: ...still waiting for LOG 13/18/23 from you ("the 5.").

Yes, I have it in mind.
This will be done when it gets cold enough again (this morning the climate control display showed 11°C).

Hello there!
May I also? The discussion about hydro power in the other link has made me curious, and after reading 5 pages, one naturally starts to form their own opinions.
I am missing .
- Compression test (cold and hot).
- Check the valve lifters on the cold engine (press down, rotate the crankshaft several times).
If everything seems to be in order, but the engine is still acting up - that's the end of the troubleshooting path.
- Check the preheating/postheating process in the assembled state of the glow plug system (using a clamp meter).
- Possibly check the tightness of the glow plug connections.
I readily admit that I don't know the construction of the preheating system on the BUK. However, if it's similar to the old 1Z (with a cable and a plug that clicks onto the glow plug), then checking everything with an ammeter connected in the circuit won't help. In my case, it was the plugs. I experienced rough starting below 5°C, coughing during startup, and uneven running for the first few minutes, even under load. Everything seemed fine according to the manual, but it wasn't working correctly in practice.
hg
Herbert.

Herbert wrote:

Hello there, May I also?

Of course.

Quote:

I miss . - Compression test (cold and hot). - Check the valve lifters on the cold engine (press down, rotate the crankshaft several times);

Therefore: since the warm engine shows completely normal data logs, I am focusing on the cold engine.
I just performed a quick compression test on the engine, which had been cooling down since yesterday afternoon (coolant temperature = 7°C).
Parked with the front right wheel raised, handbrake engaged, fourth gear selected, and the hanging wheel spun rapidly through several rotations using a wheel chock applied for compression.
A cylinder with low compression should reveal itself every four cycles through a noticeable lack of resistance, but even under the scrutiny of extremely slow rotations, I couldn't detect anything conclusive in that direction.

Quote:

If there's nothing missing, but the engine is still acting up - end of the troubleshooting path.

. .. or a detour to the software level.
While analyzing recent cold start log data, I noticed that the LRR fluctuations practically synchronize and stabilize when the significantly advanced fuel injection timing immediately after engine start is reduced back to the normal value.
Along with the varying cylinder pressures (usually 1 or 3), where the LRR data sometimes reaches its maximum limit, this seems like a promising lead for further investigation.

Quote:

- Checking the pre-glow/post-glow in the assembled (!) state of the glow plug system (using a clamp meter).

I don't have a clamp meter, but this phenomenon can sometimes be observed even above the glow temperature threshold.
That's also why I suspect the cause lies more likely in the software.

Hello Ulf,
The compression test performed in the garage is only very limited in its informative value. Have you also taken a look at the valve lifters?
Perhaps a completely different approach: What happens if you artificially feed the control unit either a very cold (with an almost warm engine) or warm (with a cold engine) temperature reading? This should be achievable by using appropriate resistors on the temperature sensor. Your comment about the possible correlation with the injection timing made me think of this.
hg
Herbert.

Here's a completely different idea: What kind of oil are you using in the engine? (Viscosity, brand)

ulf wrote:

Okay, now that the BUK has the correct 507.00 version installed, the cold starts sound and feel practically unchanged compared to the 505.01 version.

Just read everything. The type of lubricant was already discussed in detail on the first few pages. 507.00 is a 5W-30 grade.
I'm testing the 0W-30 LL2 oil on my Sharan. It's already ready to go, but I still have 5,000 kilometers (approximately 3,100 miles) until the next oil change.
Bärli, if you ever need the pressure gauge, just let me know.

Herbert wrote:

Hello Ulf,Have you already taken a look at the

tasssenstößel

Quote:

?

Yes and no:}
Approximately one year ago, as far as one can tell by removing the valve cover and observing the water pump.
In this case, the piston and connecting rod appeared normal (not seized).


}But perhaps a completely different approach: What happens if you artificially feed the control system either a very cold (with an almost warm engine) or warm (with a cold engine) reading? This should be achievable with suitable resistors on the temperature sensor. Your comment about the possible correlation with the injection timing brings me to that.} That's the other approach to my method.

For me, it's ultimately less trouble to temporarily fix the potential software bug (possibly an OEM issue). Let's see what the cold start logs reveal in the coming days...



@Deus: I use Mobil1 ESP Formula 5W30 (507.00).

ulf wrote:

... Software bug. ...

"It's not a bug, it's a feature!"

"Ulf, the current EU4+ engine control units are designed with such tight margins that even minor system deviations can cause them to malfunction immediately."
These system deviations are not necessarily caused by defects, but rather result from the accumulation of unfavorable tolerance limits.
In this assessment, it is important to consider not only the "normal" operating conditions but also the fuel being used.

I had a similar "problem" with the Forester. When it was only partially warm, the Boxer engine would shake quite violently. However, Boxers typically don't develop these kinds of "shaking moments," so it seemed strange to me.
The actual cause of the problem was the fuel. Because I can easily switch between different fuel types with a button, I was able to fix the issue. It would shake when running on gasoline, but not on gas. Another time, it was exactly the opposite; it shook only when running on gas.


I still maintain that -> Normal.


Our new EU5 CR TDI company vehicles are true world champions in their class.

"

Bertil wrote:

"It's not a bug, it's a feature!" Ulf, the EU4+ engine control units of today are so conservatively designed that even the slightest system deviation can cause them to start shaking immediately.

Okay, maybe. Nevertheless, I'd like to try, purely out of curiosity, whether addressing the suspected cause actually clearly changes the symptoms.

BTW, it's hard for the average person (colleague) to understand that a "pristine" green sticker diesel engine starts so easily and cold, and emits a horribly bright blue, stinky smoke for several seconds, like my BUK .

ulf wrote:

... BTW, it's hard for the average person (colleague) to understand that a "pristine" green sticker diesel engine starts so easily and cold, and emits a horribly bright blue, stinky smoke for several seconds, like my BUK

.

Have you ever looked at the exhaust of brand new diesel vehicles with a DPF?
I enjoy watching these new vehicles in city traffic as they start at traffic lights. They always produce a lot of smoke. That makes me wonder where the filter's effect is... because there isn't any! What your BUK does then is more or less insignificant .

Bertil wrote:

Have you ever looked at the exhaust of brand new diesel vehicles with a DPF? I enjoy watching these new vehicles start up at traffic lights in the city. They always emit so much smoke. I often wonder where the filter is supposed to be working... because it's not! What your BUK does there is rather insignificant

. Hmm... are they emitting black smoke? If so, the environmentally conscious public should react and launch protests towards the driver, car manufacturer, or BMVBS .

However, if it's emitting a light or whitish smoke, it can only be harmless "verschandeln dirt," which is something we're used to from gasoline engines (and which they happily consume in their exhaust systems).



Sure, here is the translation of the text from German to English:

"BTT:"
My suspicion that a software bug might be a contributing cause of the cold start stuttering seems to be becoming more concrete.
The original equipment manufacturer (OEM) likely managed to achieve [something] with the BUK under certain starting conditions.

a) to largely render the LRR (Lower Reference Limit) ineffective (= that high variations in the MWB13 diagnostic data correspond to minimal real-world differences, and therefore increased compensation requests reach the limits of the permissible value range at +/- 3 mg), or even...

b) to reverse the effect of the differential volume requirement (e.g., the LRR wants 1 mg more on cylinder 3, but the system delivers 0.8 mg less – these are just example values, I'm only concerned with the principle).

With a test bug fix specifically targeting the MSG software, the first three cold starts are definitely smoother than with the OEM software under similar starting conditions, and accordingly, an MWB13 log shows relatively moderate control deviations...


@ 13-18-23-Bear:
Your log is not forgotten .

Quote:

Have you ever looked at the exhaust of brand new diesel vehicles with a DPF?

Hi Bertil,

"Then those definitely aren't VAG TDIs for me, because as far as I know, all of their standard diesel particulate filters (DPFs) are closed systems. In fact, I don't know of any engine that comes with an open filter from the factory. The only way to get around it is if someone has drilled a hole in the DPF or otherwise damaged it."
In my vehicles (with BRE and CBAB engines), the inner surfaces of the exhaust pipes are definitely not coated with soot.

If the inner parts of the exhaust pipes are still metallic and shiny after 8000 km on a CBAB motorcycle, how can they possibly rust? Can you explain that to me?
While VAG sometimes makes significant mistakes, it is not accurate to attribute the current issues to the engines themselves.

Best regards, Rainer.

"Smart was the only one I know of with an open DPF. Our bus still has completely bare pipes after 75,000 km. In contrast, the TSI Golf already shows some soot in the exhaust pipe. Maybe Bertil will also start looking at gasoline engines."

Okay, here's the 13-18-23 log for Dieselbear.