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

No, I mean the idle state (the fuel injection amounts for each individual cylinder). You would recognize a "cold" cylinder by the increased fuel injection amount.
hg
Herbert.

Good idea.
I can do that, but not until tomorrow evening. I'm currently on the move.
I will report.

Unfortunately, I have to ask a silly question again: how cold does it have to be?
a) the engine (oil/coolant temperature) and
b) is it the air?

Right now, the temperature is over 15 degrees Celsius. Can you even notice any difference at that temperature, or is the preheating system completely turned off anyway, even before the operating temperature is reached?

Then I would have to wait for colder temperatures just to be able to see anything, right?

Hi,

Above approximately +5°C, the glow plug system is not noticeable with this type of engine. So, if the glow plugs were the cause, you shouldn't experience any excessive smoke or starting problems in this warm weather.

Best regards, Rainer.

That's also the case; anything above 5 degrees is like normal.
However, shouldn't the workshop be able to test the voltage and current of the glow plugs using the actuator diagnostics, even when the engine is warm? That's where the car is going tomorrow.

Florian320 wrote:

However, the workshop should be able to test the voltage and current of the glow plugs, even at warm temperatures, using the actuator diagnostics, right? The car is going there tomorrow.

Yes, to activate and measure the preheating system, you can simply unplug the connector from the coolant temperature sensor.
The engine control unit then assumes a very low engine temperature.

Best regards, Rainer.

Great, thanks!

Just a quick update: I think I can rule out the glow plug as the cause of the problem.
The car is at the Audi service center. They checked everything they could, but they definitely couldn't find any faults.
All glow plugs are drawing the expected current, and the preheating duration is also correctly adjusted based on temperature.
The relay is functioning correctly, and logically, the fuses are also intact.

Does anyone else have any other ideas about what it could be?
Otherwise, I suppose I'll have to wait until winter so that the workshop can observe the issue firsthand.

Hello Florian,

Quote:

The preheating duration is also dependent on the temperature, which is correct.

"Whenever I hear that statement, my alarm bells start ringing. Why should it be any different? Has someone written new software for the engine control unit? "

You can test the glow plugs using simple tools as described above, or completely without removing them by measuring the current flowing through the connection cable.
The cost of having a mechanic check something can be so high that you might as well buy a power meter and do it yourself.
For example, with the Peaktech AC/DC digital clamp meter 1650.
Connect the cable to the clamp and you can see which current is flowing. For each glow plug, you can expect approximately:

Quote:

The current flowing through a functional cold TDI glow plug (Bosch GSK 2 and similar types) is initially 15 amperes or more, which corresponds to a heating power of approximately 200 watts, and quickly brings the plug into the red-hot range. To prevent it from burning out during the afterglow phase, its resistance increases with rising temperature due to its design, and finally, only about 5 amperes flow through each plug.

It's faster to just use pliers than to have to drive the car somewhere.

Here's some more information about faulty glow plugs and their removal. As you can see in the specialized article on glow plugs linked at the beginning of this topic, the glow plug protrudes through a narrow hole. When the glow plug is working, it doesn't touch the spark plug; instead, oil or carbon deposits are burned away between the spark plug and the glow plug.

If the glow plug system (GSK) doesn't work, the gap between the glow plug and the cylinder head will eventually become clogged with carbon buildup, causing the glow plug to become tightly stuck. If you force the GSK to turn from the back, it can break off, and there's a risk that the front piece will eventually fall into the combustion chamber. This will damage the engine. If you're willing to take the risk, or if the GSK breaks off, you'll need to remove the cylinder head. You'll also need to replace the timing belt and other related components.

Bitte stelle Dir folgende Frage: Was soll ein Glühkerzenwechsel kosten und wer bezahlt letzteren Fall. Is everything alright?
"A bird in the hand is worth two in the bush."

Best regards, Rainer.

Hello Rainer,

That's exactly what the workshop did: they used a clamp meter to measure the current for each spark plug individually and confirmed that they were all working correctly.
So, your idea is that at least one candle is so dirty that it doesn't function properly, and that you can only see this by physically removing it, correct?
As I said: the candles are a year old, and all six were replaced then. Wouldn't that be a bit short for a failure?
"Before the exchange, three spark plugs were defective (which were checked afterwards), and the engine did not produce nearly as much smoke as it did during the filmed cold start."

So, your next idea would be to remove all the candles and take a closer look, right?

Quote:

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

No. What could possibly stick to a piece of metal or ceramic that gets as hot as 850°C?

Quote:

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

If installed correctly: yes. If installed incorrectly and simply forced into the gearbox, the clearance on the gearbox housing will be reduced, and the gearbox housing will break very quickly. See Ralf's technical article for the reason.

Quote:

Then your next idea would be to remove all the candles and examine them, correct?

No. What's the point? How did you come up with that?

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

I'm a bit confused: your statement was that the candles could be tested with an ammeter. That's what the workshop did.
Please provide the German text you would like me to translate into English. I will also include a note about potential installation errors, mentioning that they don't necessarily require the unit to be disassembled for inspection.

Assuming that each candle has been individually tested with the ammeter and behaved as expected, what is the next step if the issue is not related to the candles themselves?

I'm not sure how I should get it over here. Could it be that you're a bit naive?
Maybe you should read the topic again from the beginning and sleep on it; perhaps then you'll understand what I was trying to explain.

Apart from that, this forum is intended as a resource for people who want to repair their vehicles themselves, and not as a way to communicate between customers and workshops.

Instead of making phone calls, driving around, and then discussing the phone calls and driving experiences here, it would be wiser to actually use the measuring device yourself.

I wouldn't say I'm naive. However, I also don't automatically assume the worst of other people.
But I prefer clear communication.
If you think the workshop messed up the GK during installation and they're not admitting it, just say it directly.
That's a legitimate way to do it.
I'm not looking for someone to blame. What's important to me (and I think to all of us) is getting each car repaired.
I tried to fix it myself, but I couldn't figure it out. Luckily, a workshop appointment that was already scheduled came up.
It would have been a bit awkward if I hadn't used it, just to avoid disrupting the flow of this forum, right?

So, to put it briefly again: am I understanding correctly that, in your opinion, the glow plugs are defective - probably due to incorrect installation?
Since they are at least technically within acceptable limits, I would then only need to remove and visually inspect the glow plugs.
Okay, hier ist die Übersetzung:

"Is that correct?"

By the way, I also tested the LLR. As expected with temperatures in the double digits, the values were relatively unremarkable (I think): only cylinder 5 showed a value of -1.49, while the rest were between 0 and -1.

Quote:

So, to summarize again briefly: am I understanding correctly that, in your opinion - probably due to incorrect installation - the glow plugs are defective?

As long as you don't verify them yourself, you can't make any statements about them.