2.0 TDI CR (CAGA): Cold Start Issues & Fixes

Hello!

I have an A4 (2010) with a CAGA 2.0 TDI CR engine. The problems started with a slightly rough idle immediately after a cold start (even in the summer). Unfortunately, it's all very sporadic. For example, there are no problems for two weeks, then it happens once.
"Interestingly, the tachometer needle would briefly jump at exactly 4 seconds after the engine started. Afterward, the car would run normally. Sometimes the needle would only dip briefly, while other times it would stay low for a few seconds, and the engine would run very unevenly, as if it wasn't getting fuel. I thought it might be 'air in the system,' because it always happened exactly 4 seconds after starting. However, I couldn't find any leaks."
Unfortunately, there has never been a memory error.

"But today, something completely strange happened, which rules out the possibility of 'air in the system' again. The cold start was as usual, no rough idle immediately after starting, I drove out of the garage, everything normal (still no problem, logically, the problem only occurs immediately after the cold start). I stopped in front of the garage door to let my son get in. The engine then idled for about 20 seconds. After that, I drove off, accelerated, shifted into second gear, and suddenly the engine started sputtering and jerking, it wouldn't accelerate (no power), and it could barely maintain its speed (about 30 km/h). This lasted for about 3-4 seconds, then the engine ran normally again. And this time, I thought that with such a 'complete failure,' there *must* be something stored in the memory. But unfortunately, there was NOTHING again!"

Here's my question for the experts: What could be causing the engine to run so poorly without any error codes being stored? Could it be a "stuck" or clogged EGR valve? What component "activates" exactly 4 seconds after a cold start, causing an unstable idle?

The fact is that the two problems must have the same underlying cause. My suspicion lies with the AGR (Abgasrückführung - exhaust gas recirculation system), but that's just my assumption. However, one should be able to rule out an electrical problem, since connection errors would normally be immediately recorded in the memory. Perhaps a professional could explain this.

Mein Freundlicher sagt daß das schwer wird zu finden, da es Audi ihnen auch immer schwerer macht. Keine Sollwerte mehr und geführte Fehlersuche nur mehr bei Fehleintrag. Na super! Ich habe mich dann angeboten jeden Kaltstart mit VCDS mitzuloggen. Die Frage ist nur WAS soll ich mitloggen? II was thinking about:

Air mass (AGR rate).
Fuel pressure.
Fuel temperature.
Coolant temperature.
Intake air temperature.


"Does anyone have any suggestions on where to look for the problem? What exactly happens 4 seconds after a cold start? Something is being triggered, but what?"


Thank you for your help!

Greetings.

Hello,

You can log the fuel pressure in the advanced measurement data blocks.

Best regards, Rainer.

dieselschrauber wrote:

Hello, You can log the fuel pressure in the advanced measurement data blocks. Best regards, Rainer

Hello Rainer!

Okay, thank you, I will. But one question: Isn't the fuel pressure "monitored"? I mean, doesn't the engine control unit (ECU) throw an error if the pressure drops below a minimum level? Does only the common rail high-pressure pump (CR-HDP) build up the pressure, or is there an additional pre-lift pump in the tank for the common rail system (CR)?

Greetings.

Hi, it's me again.

Today, I did a logging run. No errors occurred yet, which would have been too good to be true. However, I need some baseline values so I can compare them if an error does occur. Unfortunately, the CSV converter isn't working correctly, so I still have to manually edit the data.

Unfortunately, I don't understand the following:
Why are the target and actual values for air mass specified in different units? Sometimes it's g/s, and sometimes it's mg/stroke. How is one supposed to compare them?

Furthermore, I'm unsure which specific blocks I should actually log.
Currently, I have:
Intake air temperature.
Throttle position.
Main injection start timing.
Fuel pressure.
Fuel pressure setpoint.
Fuel temperature.
Coolant temperature.
Boost pressure, actual value.
Target boost pressure.
Air mass value.
Air mass setpoint.
Engine start, initial amount.

I want to replace the blocks "Main injection start timing" and "Engine start injection quantity" with something more useful, because the engine always starts normally; the problems only occur sporadically after the start.

Welche Werte sind sinnvoll? Motordrehzahl? Irgendwas bzgl. AGR? What would that be?

Sure, here's the translation:

"thx"

Greetings.

Hello,

Quote:

Why are the target and actual values for air mass specified in different units? Sometimes in g/s and sometimes in mg/stroke. How is one supposed to compare them?

There are likely more entries to be found, specifically for "air mass setpoint/actual value," where the appropriate unit will appear. Just do a little searching.

It's not important to log as many different measurements as possible, but rather to log the right ones at the highest possible sampling rate.
The throttle valve position might also be an interesting parameter to consider, in addition to engine speed and fuel pressure.
Possibly, an additional log could be included, showing the injection amount in case of an error.

Best regards, Rainer.

I was just at the and asked the electrician about this issue.

He said that they had already encountered several cases of faulty injectors causing rough running, even without any error messages being stored.

@Rainer
Since the error occurs very rarely and only for a short time, I need to include as much as possible. A maximum of 12 items can be included.

I already have the throttle body adjusters. But what do you mean by "fuel injection amount"? Are you referring to the values for the 4 injectors that also control the idle stabilization? If I install those 4, then 4 other things need to be removed .


Thanks "Autoservice" for the tip. Would you also see it reflected in the values of the four fuel injectors? I'm not currently running those, as they would take up four slots.

Greetings.

Quote:

Do I need to include as much as possible

No.

Logging unnecessary data is not only superfluous, but it also results in a lower sampling rate for the interesting measurements. If the sampling rate is too low to meaningfully track changes in the interesting measurements, the entire process is useless.

You're doing it because you want to see something, not because you want to have a huge number of values in a file that then don't mean anything, right?

Regarding the injectors:
You can also find these test values in the extended measurement data blocks. Reading these test values is not critical and can always be done. It would be advisable to do so, following the suggestion from Autoservice.

"In principle, I agree with you, but I think all 12 selected blocks are useful. Do you really think the sampling rate is too low? Keep in mind that I don't have many opportunities to capture it, as it's very rare and only occurs briefly."

The thing about the injectors sounds plausible, but what surprises me is that I never had any problems after the first minute. Even if I turn the engine off again, like with the start/stop function, for example.
Ein Injektorproblem könne doch auch im warmen Zustand auftreten und außerdem, ein Injektorproblem läßt den Wagen im 2.Gang überhaupt nicht mehr beschleunigen? Es war eigentlich kein Ruckeln, er beschleunigte nicht, keine Power. Nach 3 sek. 0-Power war alles wieder normal, ohne Fehler im Speicher. Und das mehr als 1 Injektor gleichzeitig def. ist? Hmmmmm.

I find it disgusting. Such a complete failure, and NOTHING is in the memory.

Greetings.

Here are the calibration points for the injectors at different pressures for comparison, as seen on my CFFB.

Here's another VCDS configuration file for the relevant advanced measurement values.

Sure, here's the translation:

"Quick question:"
Why does my LOC 48, which displays "coolant temperature at the radiator outlet," ALWAYS show 90 degrees? Could the problem be hidden here? All other temperatures show approximately ambient temperature during a cold start, but this value is stuck at 90 degrees!

Greetings.

Okay, Loc 48 is the target value. But why is the target value already 90 degrees during a cold start?

Greetings.

Mike3BG wrote:

Okay, Loc 48 is the target value. But why is the target value already 90 degrees during a cold start? Greetings

Not all values in the extended measurement data blocks make sense or are correct.
VCDS displays the data that comes from the control unit. If the control unit sends values that are not actually used, VCDS will still display them.
This means that, compared to the "old" standard measurement blocks, it requires more careful consideration of what each value represents and whether it is even plausible.

The coolant temperature should be available in other places as well, possibly in different contexts.

Best regards, Rainer.

How can I create such a file (containing the same LOCs) and assign it, so that I don't have to re-select everything from scratch every time?

What does the "Turbo!" button mean in the advanced MWB (Material Workbench) settings?

I haven't found anything else about air mass except for the information mentioned above, unfortunately with different units.

Greetings.

Manual, page 13 and 14.

dieselschrauber wrote:

Manual, pages 13 and 14.

Okay, and where can I find these "instructions"?