A4 Cabrio 2.5TDI BDG: Gray smoke on cold start

Dear Forum Participants,

I now have another problem: since last winter, the engine has been behaving in the following way:
When the engine is cold, the starter doesn't turn over as usual in under 1 second, but feels like it takes two to four seconds.
Afterwards, the engine starts, but there is smoke for the first few seconds.
This behavior only occurs after all six glow plugs were replaced (replacement in the summer, problem started in the following winter, but of course this could also be coincidence).

Initially, it was sporadic, sometimes with long cranking and smoke, sometimes without.
However, towards the end of winter, the starting with a cold engine was always so bad.

The double temperature sensor is about 1 1/2 years old and according to VCDS, it gives plausible values. Also, the "glow plug" indicator remains on for longer at cold temperatures than at warm temperatures, so the glow plug time seems to be correct.
All six glow plugs have been checked, and all are at least within acceptable limits.

I removed the cover of the MSG today and checked the fuses: all three (2x 60A, 1x 15A) have continuity and 0 Ohm resistance.
When the "glow plug" indicator goes out, the light inside doesn't get noticeably brighter.
I performed a relay diagnosis: the glow plug relay clicks loudly and clearly from the MSG area, but the battery voltage only changes by about +- 0.5V when it switches.

The glow plugs don't produce any error messages in the fault memory.

The thought is that it's related to the glow plug system, but I'm not sure where else to look?
I hoped it was the fuses in the MSG, but they are okay.

Does anyone have any other ideas?

I have recorded both starting behaviors. The first video is in a cold state at -6°C outside temperature and after five days of standstill, the second video is after about 30 minutes of driving in a warm state.

.Mov-movies are not supported by this website.

[quote].Mov[/quote]

Thanks! Just say "it's not working" instead of trying to convert it etc.
Of course, .mov videos are supported.
Upload the video easily and let me know if the format is not accepted. Awesome, right?
Because we don't want to deal with dead links or obscure conversions after a short time, do we?

Okay, I'll do that next time. I thought it was deliberately chosen like that (perhaps due to file sizes) or that it was simply technically impossible.

Okay, here's the translation, keeping the HTML tags, BBCode tags, and URLs intact:

So im "Worst Case Video" hört man ganz deutlich, daß nicht alle Töpfe gleichmässig laufen.

Ich würde in folgender Reihenfolge das prüfen:
- Glühkerzen. Ältere TDI haben eine relativ hohe Verdichtung, so daß bei Temperaturen über 5°C die Vorglühung keine Rolle spielt.
Unfortunately, your motor video doesn't show the engine temperature at startup.
, but it's true that the compression ratio is lower in newer TDI engines. This has some advantages, but also the disadvantage that the cold start is worse and that preheating is required even at higher temperatures. Current engines also preheat during operation for exhaust reasons.

- Air in the fuel system? Have the O-rings on the diesel filter been replaced, if so?
- Compression test, now it's getting ugly because the costs for repairs can quickly reach higher amounts.

How many km has the engine done and what about the oil consumption?

Best regards, Rainer

[quote]The first video is taken in cold conditions at [color=red]-6°[/color] outside temperature and after five days of inactivity[/quote]
I'm betting on the glow plugs.

See:
<a href="viewtopic.php?t=3094">Starting problems and pre-heating system with TDI with VP37/VP44
and

<a href="viewtopic.php?t=8306">Information über Glühstiftkerzen (Glühkerzen)</a>

Best regards, Rainer

Thanks for the tips.

The headlights have all been checked six times and according to the workshop, they are technically in order.

The car has 139,000 km on it, and the headlights were replaced about 14 months ago by the Audi workshop. The problem only started after that.

The oil consumption is practically zero (or so low that it doesn't need to be topped up between inspections) - except for the initial 0.7 liters.

Could it be that instead of the headlights themselves, there is a faulty cable that is producing leakage currents and therefore not delivering enough power to the headlights? This would not necessarily be considered an error.

Edit: As you mentioned in link one, the mechanic's oily fingers could have touched the headlights and caused the problem.

Therefore, I think the first step should be to check the headlights again and also check the voltage and current flow.

Okay, here's the translation, keeping the HTML tags and URLs intact:

[quote]So, I think the first thing to do is to measure the incandescent bulbs again and check the voltage and current flow, or?
[/quote]

First, you could directly measure the voltage at the candles while they are glowing to see if voltage is present and how high it is. This would confirm that the control system is working.
When the flashing warning light goes out, the light inside doesn't become noticeably brighter.
That's normal. The disappearance of the glow plug symbol only signals to the driver: "Now the engine should start without problems." In reality, the glow plugs will continue to heat up for a while without indicating this to the driver.

Warning, here comes some dangerous pseudo-knowledge from me:
I once heard that there are different glow plugs with different preheating times and different operating voltages. However, I suspect that this is now used in vehicles with semiconductor control of the glow plugs (including individual monitoring). Since you are talking about a click-type relay, I suspect that this does not apply to you.
However, since you are talking about a small voltage drop, incorrect glow plugs with a lower current consumption could match your other symptoms. Can you read the type/part number of the glow plugs? Then check what actually belongs in the engine...
Maybe someone else knows something in this direction.

Best regards,
Guste

Hello Guste,

thanks for this idea.

The car will be going to the garage anyway on Monday (the one that also installed the spark plugs, it's an Audi center).
Even though they should theoretically know what they're doing and which spark plugs fit, it would of course be a great advantage for me to suggest this to them.

I admit, I wouldn't dare to remove the spark plugs myself and check which ones they are. If I damage something, it could become quite expensive, so I'd rather let the garage handle it.

[quote]I admit, I wouldn't dare to remove the candles myself and take a look at what they are. If I were to damage something, it could become quite expensive, so I'd rather let the workshop handle it.[/quote]
Checking or verifying would be sufficient...

Hello,

If the video wasn't -15 degrees, I would say: "It's running too hot..."

Relay or light bulb control?

Are you sure it's running on all 6 cylinders?

Best regards

[quote]It's glowing for too long....[/quote]
If it glowed instead of "normally long", but "too long", when working light bulbs, it wouldn't definitely smoke.

I think so too.

But in the video, it was actually -6 degrees, not -7, and the car had been standing for five days.

I think, under those conditions, the time was reasonable.

And yes, it sounds like it wasn't running perfectly. That would make sense if at least one spark plug wasn't working properly, then the corresponding cylinder wouldn't be working properly either for the first few seconds. You can also see in the video that the smoke disappears after about 15 seconds.

Okay, here's the translation, keeping the HTML/BBCode tags and URLs intact:

Check the LLR directly after the start.
hg
Herbert

Okay, here's the translation, keeping the HTML and BBCode tags and URLs intact:

"Do you mean the intake air target and actual values? Could it also provide information about the fuel injection start control?"