Audi 2.5 TDI VP44: Excessive Smoke?

Hello,

I'm having a problem with my 2.5 TDI that's slowly driving me crazy. Here's what's happening:
The engine is smoking quite a bit, especially when it's fully warmed up. The smoke is white and has a very pungent smell of diesel. Also, when the engine is idling, you can feel a distinct "threshold" between 2500 and 3000 RPM; you almost have to floor the accelerator pedal for it to rev higher. However, once you overcome that threshold, it revs smoothly as if nothing happened. Furthermore, it's very noticeable that when the engine is really warm (above 85°C), it starts to jerk significantly, to the point where the engine mounts can't dampen the vibrations anymore, and it's clear that it's not running smoothly. There are no error codes stored.

Basically, I've done almost everything to the engine, meaning new camshafts including lifters and hydraulic tappets, the turbocharger has been rebuilt, all seals are new, the timing belt and water pump are new, the oil pump chain is new, the entire cooling system has been completely sealed, the head gasket is new, all injectors have new nozzles and were adjusted by Bosch, and much more; so it was quite a major project .

I also correctly adjusted the VP44 using the VCDS basic setting 04. He gets enough air (the intercooler system was leaking, but that has been fixed), and he also gets enough fuel (previously, the VP44 was drawing in air, but that has also been fixed). He most likely still has enough compression (not yet measured, but he starts cold like a charm).

I suspect it might be related to the VP44. Has anyone else experienced something similar? Does anyone have any idea how to reliably determine the cause?

Otherwise, the injectors would normally be a consideration, but since they have new nozzles and were calibrated by Bosch, I find it hard to believe. I did become suspicious when I picked up the injectors and asked for a test report; the service advisor told me that the nozzles were adjusted using a manual testing device, and therefore no report was available. I thought there would be proper testing equipment for two-stage nozzle holders, but Bosch probably knows what they're doing (hopefully).

So, as I said, if anyone has any ideas or has even experienced the same problem before, please feel free to reach out, thank you .

Hello,

I suspect there might be a problem with the fuel injectors. If the injection timing is correct, but the car is smoking and smelling of unburnt diesel (not oil!), then that's likely the issue.

Check the actual and target values for injection timing using VCDS to see if they match. Logically, you should check this not at a red light, but in the load range where the smoking occurs.

The nozzle holder combinations for the VP44 are difficult to adjust precisely using a manual calibration device; they are more easily controlled.
The reason is that the opening pressures of the stages (only the first stage can be tested with a manual pressure gauge) are adjusted by spring pre-tension, and due to natural wear, the corresponding components become slightly smaller, by a few hundredths of a millimeter.
Basically, with this type of direct heat kiln, the opening pressures are always too low with new nozzles. In most cases, this is not a critical issue, but it should be checked to ensure that the pressures are not too low.

Here's my question: If the opening pressure is too low and only material can be removed from the pressure pins (!), what adjustments can be made? Because without longer pressure pins, the only option is to lower the pressure even further, which would be pointless.
So, you either have to use longer rods and grind them down – a process of grinding, measuring, and grinding again… which is very time-consuming, and the labor cost is probably something no one can afford. Or, you could grind down the sealing surface of the injector itself, which is also tricky because it needs to be perfectly flat, and the surface roughness must not exceed a certain limit.

Take a look at the idle speed control values to see if one of the cylinders (possibly the one that's smoking) is behaving differently.
Then I would perform a compression test at the bank, to make sure that the corresponding cylinder itself isn't worn out.

Best regards, Rainer.

Hi, thanks for the reply.

"Isn't it the case that the thicker the shims are, the higher the injection pressure becomes? I think that's how Bosch probably set it up. But as I said, I got suspicious when I was told that the injectors were adjusted using a manual tester, because, to my knowledge, that's not possible, at least not for the main injection. But on the other hand, a specialized Bosch Diesel Service should normally know what they're doing, or am I wrong about that?"

Regarding the measured values: The actual injection start (measurement block 004) matches the calculated value at all engine speeds. The warm-up idle control also functions correctly. The only thing I've noticed for the first time is that above operating temperature (greater than 85°C), the engine repeatedly switches between normal operation and a very rough running. It's also apparent that the idle control for cylinders 1, 4, 5, and 6 deviates significantly, and sometimes exceeds -1.5mg/stroke, which, in my opinion, clearly explains the poor engine running.
The question now is why the control unit is calculating these values...
"There are still no error codes stored, and the smoking was actually almost gone this time when the engine was at operating temperature, probably because summer is over and it's colder now. However, it still smoked quite a bit and smelled like diesel during the warm-up phase."

The DHK (injection quantity control) for VP44 injection systems is different; shims are simply used for adjustment in VP37 systems.
https://community.dieselschrauber.org/en/viewtopic.php?t=26850

VP44:
https://community.dieselschrauber.org/en/viewtopic.php?t=31836

Okay, as I said, I'm actually relying on Bosch Diesel Service to have adjusted the injectors correctly.

Furthermore, I wonder what is responsible for these fluctuations in the regulation. There must be something that detects a deviation from the idle state and requires extreme adjustments.

Quote:

The question now is only why the control unit calculates these values…

Because the individual cylinders, despite receiving the same amount of fuel from the VP44 pump, produce significantly different combustion pressures.

There are 2 possibilities:
- Cylinders showing no compression, especially those with high positive readings.
- Nozzles are dripping/leaking, or the nozzle pressure is too low (negative values), or the nozzle holes are blocked, or the nozzle pressure is excessively high (positive values).

Okay, so first do a compression test, and if that's okay, then it's the injectors.

Good luck!