A4 Cabrio 2.5TDI BDG: grauer Rauch bei Kaltstart | Posts 16+

No, I mean the idle speed (the fuel injection amounts for each cylinder). You would notice a "cold" cylinder at the increased fuel injection.
hg
Herbert

Great idea.
I can do that, but earliest I can, I'll be able to do it tomorrow evening, as I'm currently out and about.
I'll let you know.

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

Now I unfortunately have to ask again in a silly way:
a) How cold does the engine (oil/coolant temperature) need to be?
b) How cold does the air need to be?

Currently, it's over 15 degrees, can I even see any differences, or is the pre-heating system completely off even when the operating temperature hasn't been reached?

Then I would have to wait for colder temperatures in order to see anything, right?

Hi,

above approximately +5°C, the pre-heating system is not noticeable. So, if the glow plugs are the problem, you should now have almost no smoke and no starting difficulties, even in this warm weather.

Best regards, Rainer

So is it, even above 5 degrees, everything is normal.
The workshop should also be able to test the voltage and current of the light bulbs even at warm temperatures, thanks to the actuator diagnosis, right? That's why the car is going there tomorrow.

[quote="Florian320"]But the workshop should also be able to test the voltage and current of the glow plugs at warm temperatures after performing the diagnostic, right? Because the car is going there tomorrow.[/quote]
Yes, to activate the pre-heating and measure the temperature, you can simply unplug the sensor for the coolant temperature.

The engine control unit will then start from a very low engine temperature.

Best regards, Rainer

Great, thank you!

Here's a small update: I think I need to give up on the "Vorglüh" system as the cause.

The car is at the Audi workshop; they have checked everything they could, but they were definitely unable to find any fault.

All the glow plugs are drawing the expected current, and the "Vorglüh" duration is also correctly temperature-dependent.

The relay is functioning correctly, and the fuses are, of course, also intact.

Does anyone have any other ideas about what it could be?

Otherwise, I'll probably have to wait for winter so that the workshop can then examine the whole thing live...

Hello Florian,

[quote]the preheating time is also temperature-dependent, correct.[/quote]
When I make the statement, the red warning lights are already on. Why should it be different, has someone written new software for the engine control unit?

You can test the glow plugs with simple tools, as described above, or completely without removal, by measuring the current through the connection wire.
Given the cost that the friendly mechanic charges for checking, you can also buy a multimeter and do it yourself.
For example, with the Peaktech AC/DC Digital Clamp Meter 1650.
Insert the wires into the clamp and you can see which current is flowing. The expected current for each glow plug is approximately:
[quote]
The current through an intact cold TDI glow plug (Bosch GSK 2 and similar types) is initially 15 amps or more, which corresponds to an output power of approximately 200 watts and quickly brings the plug into the red glow range. To prevent it from burning out during the afterglow phase, its resistance increases due to its design as the temperature rises, and finally, only about 5 amps per plug flow through it.
Okay, I understand. Please provide the German text you want me to translate. I will translate only the readable text, leaving the HTML tags, BBCode tags, and URLs as they are.
Getting the job done with a wrench is faster than driving a car somewhere...

Also, I want to talk about faulty spark plugs and their removal. As you can see in the spark plug article linked at the beginning of the topic, the spark plug protrudes through a narrow hole. When the spark plug is working, oil/oil residue is burned between the spark plug and the spark plug.

If the spark plug doesn't work, the gap between the spark plug and the spark plug will eventually close, resulting in the spark plug being firmly seated. If you then try to turn the GSK forcefully, it can break off. This creates the risk that the front piece will eventually fall into the combustion chamber. Engine ruined if you take risks, or you remove the corresponding cylinder head after it breaks. Remove the timing belt etc., everything.

Please ask yourself: What should a spark plug replacement cost, and who pays in the event of a breakdown? Is that clear?
I immediately think of the saying: "Better to hold a sparrow than to chase a pigeon."

Best regards, Rainer

Hello Rainer,

exactly that's what the workshop did: they used a multimeter to measure the current for each candle individually and found them to be in good condition.

According to your idea, at least one candle is so dirty that it doesn't function properly, and you can only see this when you physically remove it, right?

As I said, the candles are about a year old, and all six were replaced at that time. Wouldn't that be a bit short, for a failure?

Especially, three candles were defective before the replacement (which were later verified), and the motor didn't smoke as much as during the filmed cold start.

Then, your next idea would be to remove all the candles and inspect them, right?

[quote]Your idea is that at least one candle is so dirty that it doesn't function properly, and that you can only see this when you physically remove it, right? [/quote]
No. What could be placed on a piece of metal/ceramic that gets as hot as 850°C?

[quote]As I said: the candles are about a year old, and all six were replaced. Wouldn't that be a bit short for a failure? [/quote]
If installed correctly: yes. If installed incorrectly and simply inserted into the ZK, the gap between the rings will be closed, and the GSK will quickly break. See Ralf's technical article for more information.
Then your next idea would be to remove all the candles and look at them, right?

No. What's the point? How do you figure that out?

The workshop also mentioned the decreasing resistance during the phone call, so they were aware of this phenomenon.

I'm a bit confused: your statement was that the candles could be tested with an ammeter. The workshop did this.

Additionally, you discuss potential errors during installation, but you say that they don't need to be removed for further testing.

If we assume that each candle was individually tested with an ammeter and behaved as expected, what is the next step if it's not removing the candles?

I'm not sure how to proceed. Perhaps you could re-read the topic from the beginning and give it another thought overnight. Maybe that will help you understand what I'm trying to convey.

However, this forum is intended to be a resource for people who repair their own vehicles and not a private channel for discussing issues with their mechanic. :idea:

Instead of calling around, driving around, and then discussing the issue here, it would be more efficient to simply use a diagnostic tool.

Not naive - I wouldn't say that. But I also don't assume anything about others.
But I value clear communication.
If you think the garage messed up the glow plugs during installation and doesn't want to admit it, then just say so.
That's a legitimate possibility.
I'm not concerned about assigning blame. I (and I think everyone) want to get the car back in working order.
I tried myself and couldn't get anywhere, then a planned garage appointment came up.
It would have been a bit strange not to use it, wouldn't it, to avoid disrupting the understanding on this forum?

So, to summarize: am I right in thinking that, according to you, the glow plugs are probably defective - likely due to incorrect installation?
Since they are at least technically okay, the only remaining options would be to remove them and visually inspect the glow plugs.
Right?

By the way, I also tested the LLR. As expected at two-digit temperatures, the values were relatively unremarkable (I think): only cylinder 5 was at -1.49, while the rest were between 0 and -1.

[quote]Also nochmal kurz zusammengefasst: verstehe ich richtig, dass Sie Ihrer Meinung nach -wahrscheinlich aufgrund eines falschen Einbaus- defekte Glühbirnen haben?[/quote]
Da man sie nicht selbst überprüft, kann man dazu auch keine Aussage machen.