A4 Cabrio 2.5TDI BDG: grauer Rauch bei Kaltstart | Posts 48+

That looks good, we can leave it as is. So, the problem is definitely not related to the pump adjustment of the VP44.

Oh, thank you for the quick reply!

What I forgot to mention is that the transparent tubing leading to the VEP device never had any air bubbles, at least not when I was fiddling with it and looking at it.

So far, my assessment is that the glow plugs seem to be working correctly (as far as I could test them), the injection timing is correct, the fuses in the MSG housing are intact, and the dual temperature sensor is displaying plausible values.

Now I'm wondering: what should I check next?
The Audi service technician suspected a leaking fuel injector when he saw the video of the cold start.
I can even understand that, because it certainly looks like unburned diesel fuel.
Nur: warum leckt sie dann nur, wenn es kalt ist? Does it exist?

Where would you suggest we look next? Is it possible to narrow down the 'health' of the injectors using VCDS in any way?
Regarding the idle speed values, cylinder 5 is just barely outside the acceptable range, with values reaching up to -1.7. Could this be a possible indication of a problem?

Quote:

Is it possible to limit the 'health' of the injectors in some way using VCDS?

"It's a mixed result; the idle speed control indicates problems with the injectors, as well as differences in the compression of the individual cylinders. However, 1.7 mg/H is still acceptable, and I would consider any value below 2.0 mg/H to be perfectly normal."

I'm afraid that further troubleshooting only makes sense when it's cold again. Another possibility could be a coolant temperature sensor that only provides incorrect readings in cold temperatures; I've experienced that before.

Otherwise, just continue to monitor the situation; now the car is running.

Best regards, Rainer.

Hello Rainer,

You're probably right. Thanks for your tips.
Unfortunately, the temperatures rose so much during the winter that, by the time I got an appointment, the phenomenon no longer occurred.
Otherwise, the car drives perfectly. So, I guess we'll just have to wait and see what the winter brings.

Okay, it's finally cold. The outside temperature displayed on the AI system was 3.5 degrees, and the coolant temperature initially was 6.6 - I think that's an acceptable difference.

I've now proactively fully charged the battery to rule it out as a potential cause of poor glow plug performance. However, I had driven for a long time beforehand, and the charger (CTEK) finished its cycle in less than 3 hours, so the battery was already relatively well charged.
By the way, this engine start was, I think thanks to the long time it takes for the ignition to engage before the engine starts, similar to what's shown in the video: it took a longer cranking time (1-2 seconds longer), produced a lot of blue smoke, but the engine didn't run quite as unevenly.
One could naturally conclude that this is indeed the preheating system, but the engine is running more smoothly than in the video because all cylinders were equally poorly preheated, right?

Attached is a log, but more than 60 seconds passed between ignition and engine start because an HW update to version 1.96 was performed in the meantime.
I have to try it again, but I'm still attaching the log here.

Are the key performance indicators (KPIs) I have chosen meaningful and informative?

And: I need a few seconds to select the spark plugs, and in that time, the glow plugs are probably already cold again. Will I "lose" the selected spark plugs if I briefly turn the key back to the ignition position and then back on, or can I get real values like that?

Hi,

Please provide a vehicle scan so we can learn more about the car. You mentioned that the glow plugs were replaced, but how do you know that the correct ones (in terms of length and resistance) were installed?

Best regards, Rainer.

Hello Rainer,

Attached is the car scan. The last scan, about five months ago, showed no errors.
The phone issue is likely due to the Kufatec Bluetooth module that I recently installed and configured.
The error in the door control unit is new - I was rear-ended and the rear bumper was replaced. Could it be that something went wrong during that repair?

...and I don't know if the correct spark plugs were installed.
I had it replaced by the local Audi dealer.

Okay, and now here's the appendix as well...

...and another log entry related to cold starts. The first few seconds after the start are missing, as the control unit needs a few seconds to become fully operational again.
At least, I can see from both logs that cylinder number one is particularly noticeable. Or, alternatively, cylinders 3 through 6...

With idle speed adjustment values between -2.0 and +2.0 mg/H, that seems appropriate.

Best regards, Rainer.

Hello Rainer,

Thank you for your assessment.

It still makes sense to continue checking the spark plugs, right?
After starting the engine with 1 minute of ignition, the smoke and starting behavior were very similar to a "normal" faulty start in cold weather, only worse.

One could infer from this that the preheating system is indeed the source of the problem.

Hi,

Quote:

However, it still makes sense to continue checking the spark plugs, right?

Since the probability of a mixed configuration is quite low, it would be sufficient to remove one glow plug and check its functionality and that it is the correct model.

Best regards, Rainer.

I'd also like to add my two cents.

Since the static settings of the VP44 are correct, and the idle speed control is also working.
It wouldn't suggest that there's a mechanical problem with the engine.
actually listened to Rainer's advice and checked the type of spark plugs.

Here's my experience with the engine: add just a fingertip's worth of oil.
Pour diesel fuel, or whatever is currently available, into the recess with the glow plugs.
Start the engine and see if it's bubbling. Then, clean it again.

It can be extremely difficult to get this right. Now, if the conscientious...
For the Audi apprentice, tightening the spark plug with the specified torque is crucial.
The lawn is green, but possibly the glow plugs are not sealing properly in the cylinder head.

Regards,
Sascha.

Hello Sascha,

Thank you for your reply!
I'm currently on vacation and therefore not near the car, but I will check (or have checked) the type of spark plugs installed at the earliest opportunity.
It really seems like there's a mistake in that area.