2.5 TDI Starting Problems: Troubleshooting Guide

Hello community,

Sure, here is the translation of the text from German to English:

"The following is the initial situation:"

Audi A4 Avant, engine code BDG, 120 kW / 163 hp, manufactured in 2004, 300,000 km mileage, Euro4 emissions standard.

I'm the original owner, and I've been struggling for years with my A4 having difficulty starting at certain outside temperatures. It starts fine in cold weather, but when the engine is hot or still warm, it also starts well. The problem occurs when the outside temperature is around 10°C and the engine is cold. Then, the starter motor "grinds" for almost 5 seconds before the engine starts, and a white cloud comes out the back.

The usual suspects were checked.
- Glow plugs (all new)
- G62 sensor.
- Ignition timing
- Starter speed
- Battery (new)
- No air bubbles in the system.

About a year ago, I noticed that the problems described above didn't occur when I used ARAL Ultimate Diesel. I've now driven for almost 10 full tanks of this expensive diesel and haven't experienced any starting problems since.

Until recently, premium diesel grades were said to contain 0% biofuel. That's why I attributed the better starting performance to them. However, recently I read at the fuel pump that even premium diesel now contains 7% biofuel. Therefore, my hypothesis cannot be correct...

The day before yesterday, I unfortunately had to fill up with "regular" diesel again. The next day, the familiar problem arose: an outside temperature of 8.5°C, the starter motor whirred, and a cloud of white smoke appeared!


Does anyone have any ideas about what else it could be? There must be some difference between the different types of fuel, which is why my diesel engine reacts so sensitively.

Maybe someone can shed some light on this – I'm grateful for any advice!

Thank you very much and best regards.

netrocker

Common problem, my Audi does the same thing, and my future winter car, a Passat Variant 3BG 2.5 TDI 4-Motion with a BDH engine, will likely have the same issue.

Try letting it glow twice and wait until the relay switches off, then start it, and your beets should start properly.

Hello Ruedi,

Thank you for your response, but I've already tried this workaround many times, and unfortunately, it doesn't work in my case.

The engine only starts without any problems when I use premium diesel.

And I would like to know why (*curious*).

Regards,
netrocker

A higher cetane number results in better ignition quality. That's basic physics!
It's difficult to assess, from a distance, why your mill is experiencing starting problems under certain conditions without a proper diagnosis.
Therefore, the advice is: purchase a diagnostic system from this shop and buy the corresponding repair manuals from the vehicle manufacturer. With this equipment and the willingness to understand the technology, you will have the perfect conditions to solve these problems.
I would also consider performing a compression test.