A6 TDI: Hard Starting & Grey Smoke - Troubleshooting

I have an Audi A6 from 1996 with 140,000 km. When I start it in the morning or after work, it doesn't start on the first try, but only starts after about 5-6 seconds. This happens when the outside temperature is around 10°C. However, once the engine has been running for a minute or so, it starts immediately on the first try. Additionally, there's a gray smoke cloud coming from the exhaust pipe during the initial start. Does anyone recognize this problem, or has anyone heard of something similar? The glow plug system only activates below 8°C outside temperature, so I don't think it's the glow plugs. I just noticed that I only have a 64Ah battery installed (new since buying the car, about 1 month ago). Could this be due to the battery? I had the same capacity in my previous 2.3 gasoline engine, but it seems too weak for the 2.5 TDI. Does anyone know what the required battery size is for a TDI A6?

Furthermore, the brake warning light is illuminated, and there are three short beeps .
I already took it to the workshop, and the diagnostic tool didn't find any errors.
Please provide answers as I am facing a major puzzle... thank you.

In a gasoline engine, there's a so-called pressure accumulator that prevents the formation of vapor bubbles in the fuel system. Something similar likely exists in a diesel engine as well. While I don't believe vapor bubble formation is an issue in diesels, there still needs to be enough fuel available for immediate starting without excessive cranking.
Unfortunately, I don't know what this part is called on a diesel engine, but a workshop will definitely be able to identify it based on this description.
Let's have that checked.

Regarding the battery... I have a 1996 Audi A6 with 140 horsepower, a 2.5L engine, and air conditioning.
I believe there isn't enough space for a larger battery under the rear seat. Mine only has 64AH. I have a parking heater that also functions as an air conditioner in the summer, and it works perfectly fine.

I wouldn't worry about that...

Unfortunately, I don't recognize that brand of hearing aid.

I wish you good luck.
Regards,
Wool

Hi there,

The starting problem might be related to a temperature sensor. You can disconnect it, which will cause the control unit to register a low outside/engine temperature. If this resolves the starting problem, then the issue is likely due to the temperature sensor.

The brake warning light illuminates, accompanied by an audible signal, because the ABS system temporarily deactivates due to low voltage.
When starting the engine, the battery voltage drops significantly due to the high current draw of the starter motor. The ABS system deactivates when the voltage falls below a certain threshold, which I believe is around 9.5 or 10 volts.
But don't worry, it turns back on immediately afterwards when the generator ensures that the voltage in the electrical system rises again.
If your car is equipped with additional instruments, you can directly observe the effect on the voltmeter.

I suspect that this might not necessarily be related to the battery size or condition. My A6 sometimes deactivates the ABS when starting, especially when it's cold and being preheated. I initially thought the battery was failing and wanted to buy a new one. However, the battery test showed that everything is still within the normal range, so I'm just living with this "problem."

It might be helpful to check the battery connection cables. You could try disconnecting them, moving them slightly, and then reconnecting them securely, or applying some terminal protectant.
Before you start, locate the radio code if an original radio is installed, as it will revert to its coded state when the battery is disconnected.

Another possible cause could be an incorrect battery type.
Diesel engines must be able to deliver a significantly higher short-circuit current despite having the same capacity as gasoline engines; therefore, diesel batteries are always more expensive than comparable batteries for gasoline engines.

If everything else is okay, then the only remaining issue is likely a problem with the starter motor, which can be checked at a Bosch service center.

HTH.
Olli.

hello!

Well, it turns on when you unplug the cable.
Could it also be related to the initial amount?


Hi,

The starting problem might be related to a temperature sensor. You can disconnect it, which will cause the control unit to register a low outside/engine temperature. If this resolves the starting problem, then it's likely due to the temperature sensor.

The brake warning light illuminates, accompanied by an audible signal, because the ABS system temporarily deactivates due to low voltage.
When starting the engine, the battery voltage drops significantly due to the high current draw of the starter motor. The ABS system deactivates when the voltage falls below a certain threshold, which I believe is around 9.5 or 10 volts.
But don't worry, it turns back on immediately afterwards when the generator ensures that the voltage in the electrical system rises again.
If your car is equipped with additional instruments, you can directly observe the effect on the voltmeter.

I suspect that this might not necessarily be related to the battery size or condition. My A6 sometimes deactivates the ABS when starting, especially when it's cold and being preheated. I initially thought the battery was failing and wanted to buy a new one. However, the battery test showed that everything is still within the normal range, so I'm just living with the 'problem.'

It might be helpful to check the battery connection cables. You could try disconnecting them, moving them slightly, and then reconnecting them securely, or applying some terminal protectant.
Before that, find the radio code if an original radio is installed, as it will revert to its coded state when the battery is disconnected.

Another possible cause could be an incorrect battery type.
Diesel engines must be able to deliver a significantly higher short-circuit current despite having the same capacity as gasoline engines; therefore, diesel batteries are always more expensive than comparable batteries for gasoline engines.

If everything else is okay, then the only remaining issue is likely a problem with the starter motor, which can be checked at a Bosch service center.

HTH.
Olli

Hi there,

The initial fuel quantity might be a cause. Perhaps the static injection timing is also not set correctly or has been adjusted incorrectly.
Has the timing belt perhaps been replaced recently?

Olli.

'The timing belt was replaced at 110,000 kilometers... now I have about 146,000 kilometers on it.'

Hi,

The initial fuel quantity might be a cause. Perhaps the static injection timing is also not set correctly or has been adjusted incorrectly.
Has the timing belt perhaps been replaced recently?

Olli

Hi there,

Then the timing belt would actually be irrelevant, unless the second timing belt for the ESP hasn't been replaced.
Did the effect appear suddenly, or was it a gradual process?

Olli.

Hmm, that's a good question... I've only had the car for a month.
Perhaps the previous owner didn't even notice it, or maybe they just didn't pay attention because it was only the first start. I have no idea.
Okay, I'm going to change the diesel filter now, and maybe stop by a Bosch service center. It's not a critical issue, but I would be happy if it were resolved.



Hi,

Then the timing belt would actually be irrelevant, unless the second timing belt for the ESP hasn't been replaced.
Did the effect appear suddenly, or was it a gradual process?

Olli

Hi!

I'm driving the same car and I've experienced this problem too.
"In my case, the chip in the engine control unit was incorrectly programmed (set to ignition instead of glow plug). After I replaced it, everything was back to normal and the glow plugs worked again."
However, that won't be the case for you.
Possible causes: Incorrect injection timing, clogged diesel filter, faulty glow plug system or worn-out glow plugs.
Although I'm leaning more towards options 1, 3, and 4.
If it doesn't pre-glow properly, it will have to ignite through compression, and that can take some time...
One more question: Does it run roughly for a short time when it starts up?


cu: Marko

P.S.: If the brake warning light comes on, the battery is probably nearing the end of its lifespan!

hello!

'So, mine runs smoothly right away after it starts.'
Actually, the engine should only start to glow when it's below 8°C, according to the owner's manual. So, my girlfriend has a 1.9 TDI VW, and just like mine, the preheating indicator light comes on and then goes off after about one second.
Hmm, what does 'chip' mean in the engine control unit (ECU)? Can it reconfigure itself or something like that?


Hi!

I'm driving the same car and I've experienced this problem too.
'In my case, the chip in the engine control unit was incorrectly programmed (set to ignition instead of glow plug). After I replaced it, everything was back to normal and the glow plugs started working again.'
However, that won't be the case for you.
Possible causes: Incorrect injection timing, clogged diesel filter, faulty glow plug system or worn-out glow plugs.
Although I'm leaning more towards options 1, 3, and 4.
If it doesn't pre-glow properly, it will have to ignite through compression, and that can take some time...
One more question: Does it run roughly for a short time when it starts up?


cu: Marko

P.S.: If the brake warning light comes on, the battery is probably almost at the end of its life!