Kraftstoffilter von ATU - Startschwierigkeiten ??? | Posts 16+

Hi!

I'm experiencing the exact same temperature issues.
It seems to be some kind of AAT-related issue.
The bubble has nothing to say, and it's the same for me.
However, I haven't been able to figure out where it comes from.
It's possible that there's a leak somewhere in the system, or that the automatic venting isn't working correctly.


Best regards: Marko

Hi,

@Marko:
It's good to know that there are other AAT enthusiasts who share the same problems!
(But it's not that I want anyone to have any problems!!! )
Has your car had that problem for a long time, maybe since the beginning? I'm interested because mine is a used car.
At VAG, I was told that it was due to an air bubble (as I said, I don't entirely believe that). Furthermore, they stated that it wouldn't matter to the engine if it shook for a few revolutions after a cold start.

Hi!

That's a typical "I don't know what to do" statement from Volkswagen.
Okay, let's get started and roll up our sleeves...
If your car shakes when starting, it could be the glow plugs.
Just try this: disconnect the temperature sensor (so that the warning light stays on) and then try starting the engine.
If it then starts perfectly, you'll know it's the spark plugs, or that they're faulty, because it will start just as roughly otherwise.
Otherwise, all that remains is the glow plug system, fuel injectors, etc.
As I said, claiming that an air bubble was the cause is probably nonsense.

cu: Marko

Hi,

I could have written that down just now.
'The glow plug system is working correctly (I tested it myself by disconnecting the sensors, and the workshop also checked it thoroughly). The injectors are also in good condition; they were inspected and cleaned at the workshop. The previous owner likely drove the car mostly for short distances, as the injectors were quite dirty.'
It didn't help.
When I find my generous spirit again (which I seem to have misplaced at the moment), I'll get him a new diesel filter (due to a leak) and a new temperature sensor.
Unless you've already tried that...

Hi Markus!

I've already tried everything, but it hasn't worked.
I'm going to focus on Christmas for a while and then I'll post again...


Cu: Marko

Hi Marko,

/viewtopic.php?t=232

That's the only thing I can think of right now.
If the initial fuel amount during a cold start is insufficient (which is likely at freezing temperatures, since it starts up very well then), it would probably be necessary to increase it.
Unfortunately, I don't have a VAG-com, and when I contacted Audi technicians, they said that the initial fuel quantity is pre-calculated and cannot be changed.

Well, I'm looking forward to hearing your insights about Christmas!

Markus H. wrote:

At VAG, I was told that it was due to an air bubble (as I said, I don't entirely believe that). Furthermore, they stated that the engine wouldn't be affected even if it shook for a few revolutions after a cold start.

Hi!

Since the seal on the ESP drive shaft was replaced, there are no more air bubbles! I had it replaced by Henzo at dieselsend.de! You can also do it yourself, but if the shaft is slightly corroded, it needs to be reamed.

At VW, they install check valves as an alternative. However, I think it's nonsense because eventually diesel fuel will leak out of the sealing ring!

"However, my cold start problem hasn't improved, which means the ESP probably has some tolerance for air bubbles. They just can't be too large!"

Best regards, Christian.

Hi,

@Christian:
Thank you for the tip!
I only suspect that it might not be due to the (rather large) air bubble.
It's more related to an 'unfavorable' outside temperature.
It starts shaking approximately 2 seconds after startup, at a temperature between 5 and 10 degrees Celsius.
Now, in this Siberian cold, it starts up like a young god!
I've never experienced anything like this in any other car!
But it seems like Marko is aware of that too...

Hi Markus!

Problems keep bothering me, so I've already tried a few things.
Since I was already having the timing belt replaced, I took the opportunity to carefully check all the timing settings again to make sure everything was correct.
I added some fuel and it started without any problems (no sputtering, no misfiring, no smoke...).
I suspect that this shaking is caused by incorrect valve timing.
Furthermore, the ESP (Electric Stability Program) tends to recalibrate over time, which can further amplify the effect!



cu: Marko

Marko wrote:

Since I was already having the timing belt replaced, I took the opportunity to carefully check all the timing settings again to make sure everything was correct. I added some fuel and it started without any problems (no sputtering, no misfiring, no smoke...). I suspect that this shaking is caused more by incorrect valve timing. Furthermore, the ESP often drifts over time, which further amplifies the effect!

Hi Marko,

A few questions:
Did you also check the timing with the old belt?
If so, how "wrong" were they?

Could the old belt have stretched? In other words, were the tension markings on the pulley far apart?

Hi Ulf!

Before the actual assembly: Remove the cylinder head cover and rotate the engine until the mark at the rear and bottom aligns with the vibration damper.
During the process, I noticed a slight deviation (the front camshafts weren't fully open).
Remove the old belt, adjust it properly and precisely, put on the new one, and there you go...
As I said: without any problems, in perfect and quiet (not rattling) condition.
Run.
The belt still looked relatively good, and the tensioner pulley markings appeared to be within the acceptable range upon visual inspection.


Best regards: Marko

Hi,

@Marko:
Congratulations! One less problem.

I wonder if the same could happen to my AAT, since the timing belt was replaced specifically when I bought it in September.
Actually, the Audi workshop should be able to fix that.
Therefore, I cannot use the starting behavior with the old belt as a basis for comparison.

Furthermore:
I never need to use the choke, whether the engine is warm or cold.
He doesn't make excessive noise. The performance is good. The amount of soot also seems normal to me.
The only thing is, it shakes for 2-3 seconds after starting when the temperature is between 5 and 10 degrees Celsius.
IF it were the misaligned belt, wouldn't the factors mentioned above cause problems?

Markus H. wrote:

The only thing is, it shakes for 2-3 seconds after starting when the temperature is between 5 and 10 degrees Celsius. IF it were the misaligned belt, wouldn't the factors mentioned above cause problems?

Hi Markus,

Shaking only after cold starts usually comes from individual faulty glow plugs - or from poor compression in the affected cylinder .

Hi Ulf,

The spark plugs are in good condition.
They have been tested and function perfectly even in sub-zero temperatures.

Compression?
The engine has only been driven 116,000 kilometers.
It also starts immediately in sub-zero temperatures (recently -10 degrees Celsius) and runs smoothly.

That's exactly what's so annoying.
He only shivers more frequently when the temperature is around 5-10 degrees Celsius.
As if the initial amount were too small.

I probably need to have the ignition timing checked, and possibly also the temperature sensor. If the temperature sensor is sending high temperature readings to the engine control unit (ECU), the fuel injection quantity might be too low.