Kniffelaufgabe: Ursachen für unrunden PD-BUK-Kaltstart? | Posts 80+

Hi Ulf!

Ah, he's alive again .

Would you also occasionally upload a 13/18/23 log at approximately 10°C and operating temperature?
Terms and conditions as stated above.

Thank you in advance & best regards!

DieselBär30x wrote:

Would you perhaps upload a 13/18/23 log at approximately 10°C and operating temperature sometime? Conditions see above.

I actually don't like that exact combination of 13/18/23 because it doesn't include either the quantity or the speed.
"For me, the value of 23 isn't very informative because for about 20 seconds after starting, all cylinders show a reading of 0."

Around the age of 18, I haven't really paid much attention to it so far, but I might catch up on that soon -> I will then record the date as 1/13/18.

Hmm. Are you really not going to log a 13/18/23?
"I'm only interested in the comparison for now."
I would like to know when the control loops for each parameter (BIP) reach their setpoints and, if they do, what values they stabilize at.
I don't currently see a causal relationship between the controlled motor start moment and the fuel injection amount *sorry*.

Best regards!

DieselBär30x wrote:

Hmm. Are you perhaps willing to overcome your hesitation and log a 13/18/23? "I'm only interested in the comparison for now." I would like to know when the control loops for the BIP each lock in, and if so, with which values.

To avoid you having to wait any longer, here is a combined log from starts 1-13-23 with 6 launches from the BUK.

Okay, I'm ready. Please provide the German text you want me to translate into English.

Hi Ulf!

Thank you for uploading it first!

How beautiful must the eyes be that I have to create for you in order to get a 13/18/23 combination?
I'm interested in how the MWB 18 behaves at your place, specifically before, during, and after its start-up. Does it engage within 2 seconds, or does it take up to 50 seconds like with some other models?

Your log was taken at +5°C. Did you pre-heat it then? Does it still have starting problems at 0°C or 5°C? At what (outside) temperature does it start cleanly? Or is this also the case in midsummer?
However, in your log, all 4 PDEs are actually running at their maximum clock speeds, which is something that isn't as clearly visible in any of the other logs uploaded here.

Thank you in advance for the 13/18/23!

Best regards from Munich!

DieselBär30x wrote:

How beautiful do the eyes have to be that I have to create for you in order to get a 13/18/23 combination?

I am waiting for your ideas / suggestions.

Quote:

As I mentioned before,

I was interested in how MWB 18 performs on your system BEFORE, DURING, and AFTER the start. Does it engage within 2 seconds here, or does it take up to 50 seconds like with some other systems?

Quote:

Okay, I'll do a 1-13-18 test specifically for you sometime. But it will probably take a while...

Your log was taken at +5°C. Did you preheat it then? Does it still have starting problems at 0°C or 5°C? At what (outside) temperature does it start cleanly? Or is it like that even in the middle of summer?} I don't remember whether it was preheated. The tendency seems to be "the colder, the more stuttering," but I can't see a reliable and accurate connection between stuttering and LRR data.
Over the summer and so far, the engine has always started smoothly based on what I've heard. Roughly speaking, I estimate that below 10°C water temperature, noticeable irregularities will start to appear shortly after starting the engine.

ulf wrote:

At some point, I'll make a 1-13-18 blend especially for you.

But it will take some time. Well, today I managed to do it.

@Bear: The new logo has been inserted below in the updated :mrgreen:upload section; the link is as mentioned above.

Now, I want to read detailed analyses of the data from the year 2018 from you, and I want them right away }.

Hello and thanks again!

Was a cold start? The LLR values look very different this time compared to your last log. Did it stutter here as well?

DieselBär30x wrote:

Was a COLD start?? The LLRR values look very different this time compared to your last log. Did it also stutter here?

Yes, a "cold" start after about 2 weeks of standstill without preheating.
He also stuttered a little.

Okay, so in the last few days, it's started again with stuttering and white-blue smoke on cold starts, which indicates unburned diesel fuel.

Here's a fundamental question (and a few follow-up questions for the motor experts):
Under what conditions will injected diesel fuel fail to ignite?

1. Insufficient compression (for the current temperatures). In my case, this should only occur when the engine is cold, as the warm "idle test" is normal.
I suspect the cause might be excessive oil pressure, which could pump up the hydraulic lifters into a range of "negative valve lash" – but this would only last for about 15 seconds after a cold start! Is something like that even possible?

"Fuel injection amounts below the ignition threshold. Is there any other explanation for this besides air entering the common rail injectors, which is then purged from the system after approximately 15 seconds?"

3. Poor atomization in certain PDEs, which cannot be immediately compensated for by increasing the LLR (Low-Temperature Combustion) amount to achieve successful ignition. A possible cause: Carbon deposits around the injector nozzles.
Can the ignition conditions improve significantly within about 15 seconds after a cold start, to the point where the poor atomization suddenly becomes sufficient?
And could all these problems disappear just about a minute after a cold start (and even sooner with a warmed-up engine), to the point where the long-term reliability indicator (LLR) can return to its normal range?

Hi Ulf,

Quote:

A possible cause that comes to mind is excessive oil pressure, which could pump the lifters into a range of "negative valve lash" - but this would only last for about 15 seconds after cold starts!? Is something like that even conceivable?

However, it is also conceivable that a hydro accumulator could collapse due to prolonged inactivity and require repressurization before the corresponding valve can open.
It should then be audible as a "tick-tick-tick" sound.

Just increase the preheating time or preheating conditions; you know how to do it .

Best regards, Rainer.

dieselschrauber wrote:

It is also conceivable that a hydro accumulator could collapse due to prolonged inactivity and needs to be pressurized before the corresponding valve can open. It should then be audibly heard as a "tick-tick-tick" sound.

Hmm...

1. I have never heard such a ticking sound before.

2. In my opinion, it is hardly conceivable that this hydraulic fluid would not break down throughout the entire summer, or that the motor selectively leaks only between October and April when parked, such that the valve remains open .

Quote:

Just try increasing the preheating time or preheating conditions; you know how to do it

. I already tried that last winter (preheating multiple times in a row before starting), but without any clear success .

I have the preheating time set to 32700 on my Sharan, and I also have the long-reach spark plugs installed. Nothing changes.
The Passat with the short wheel base only exhibits these behaviors in extremely cold temperatures.
It would be interesting to try LL2 oil with a viscosity of 0W30 that meets the 50601 standard. However, there are still 6,000 kilometers until the next oil change.
Preheating is helpful, even short heating times are sufficient.

Hello everyone!

I also experienced this "clicking" issue with my problematic AXC engine, which continues to occur in idle mode (i.e., with the throttle closed!), but NOT (!) when the ignition is turned off simultaneously.
If the shut-off valve is deactivated, does the "clicking" sound continue even when the ignition is OFF?
@Ulf, try disconnecting the U-shaped hose at the shut-off valve and see if you can reproduce my phenomenon with/without it. If you can, then we would be facing exactly the same problem .

By the way, I (at that time) completely replaced all the hydraulic components for a good price (original parts!), but it made absolutely NO difference or improvement! I initially suspected there was a problem somewhere in the valve mechanism.

Steffen advised me here (via private message) to urgently check the pressure output of the tandem pump to see if it's working correctly – something I haven't been able to do yet because I'm still having issues with my ear canal, doctor's appointments, etc.
He also reported on another AXC vehicle in the fleet that had been experiencing similar issues since the beginning – starting poorly at temperatures below approximately 0-15°C!
For me, even a short pre-heating period using the auxiliary heater helps to ensure a perfect start without any (hard) combustion interruptions or excessive white/blue smoke from the exhaust.

"Definitely, the AXC engine always starts relatively smoothly as soon as someone is standing behind the exhaust with a camera and simultaneously taps into the OBD port for logging *damn* In the morning, no one is watching, and it's in a hurry, so it misfires heavily with abundant combustion interruptions for about 30 seconds ".
That's why I've also been quite reserved up until now.

It was just a condolence post for Ulf, but maybe he could test the "clicking" sound during operation with and without the active bypass valve engaged.

Best regards from Munich!

PS: @ Ulf... I'm still waiting for a simultaneous(!) and verschandeln log file named "KaltStart_MWB_13_18_23.csv" .

DieselBär30x wrote:

It was just a condolence post to Ulf, but maybe he could test the "clicking" sound during operation with/without the active shut-off valve?

No: because I think it's pointless, because mine doesn't click even in the normal setup.

The only thing I hear is a slightly louder knocking sound from one of the cylinders when accelerating from a standstill. However, this disappears even without any load at idle, and especially in forward thrust.

Quote:

PS: @ Ulf... I'm still waiting for a simultaneous (and clean) log file named "KaltStart_MWB_13_18_23.csv".

Oh dear... Okay, I will do that soon.

DieselBär30x wrote:

Has a solution to your problem been found yet? "I'm experiencing a similar problem with my T5, where there are combustion interruptions within about 2-5 seconds after a 'cold' start. The issue seems to worsen as the starting temperature approaches the glow plug activation threshold of 5°C. Currently, I'm already having problems when the temperature is below 18°C." Now Steffen, GTI and I are puzzling over the causes...

In the meantime, I am sifting through the software of the BUK engine, other 1.9L PD-TDIs, and the 2.0L BPW engine, which, according to the records, has the same PDE as the BUK.

My current assumption is that the stuttering cold starts are, so to speak, partially caused by software and become apparent as soon as the hardware reaches a certain level of wear (i.e., slight differences between the cylinders) - through the way the quantity compensation system escalates .


In the initial tests with modified data (towards older EU3 engine specifications), the freshly cold-started BUK (even without afterglow) certainly didn't exhibit as much surging as it did with the OEM software .