Tapping Noise in Cold 1.9 TDI PD Engine: Problem?

Hello,

After cold starts around 0°C, and for about 1 minute and 30 seconds, there's a noticeable knocking sound from one cylinder when accelerating on the first slight incline, even before reaching the main road. This is most noticeable in the range of 1200-1400 rpm; above 1500 rpm, it's barely noticeable. As the engine warms up, it becomes increasingly difficult to provoke the knocking.

The only parallel in the diagnostic data is the high level of oxygen imbalance readings in the MWB 13, sometimes reaching the regulatory limit of +/- 3 mg, while there is a noticeable knocking sound.
Whether the engine is idling or under load, the still-cold engine runs smoothly and quietly (although it may cough or sputter immediately after starting).
The sound quality is also perfectly fine.

DIY compression tests (spinning the front wheel on a jacked-up vehicle with the gear engaged and the engine cold, and a downhill "rocker" test with a warm engine) show no significant differences between the cylinders.

Is this knocking sound a cause for concern, potentially indicating gradual hardware damage?
Where could the noise be coming from?
A possible partial answer: It's likely that the start of injection plays a role, especially if it's individually determined for each cylinder based on the differing injection quantities. The weakest cylinder, receiving the highest injection quantity, would then have the earliest start of injection. Does this automatically cause a louder knocking sound in the cold engine?

Or, in a PDE (pre-diesel injection) system, could only the pre-injection process potentially be incorrect, as long as the hardware is cold?

Hello Ulf,

I've been through the same thing. I've checked all sorts of things (crankshaft position sensor, camshaft position sensor, pressure sensor wiring harness), but without success.
Months later, out of curiosity, I adjusted the camshaft timing. Before doing so, I read the correction angle. VCDS showed a value of +0.3°, meaning the camshaft was set later than it should have been. I then adjusted it to -0.5°, which means setting it earlier (VCDS shows you where you *should* be, not where you *are*).
"I was very surprised that it now starts immediately even at -15°C, and runs smoothly without any coughing or shaking. The fuel consumption has decreased by 0.3 liters, and it runs noticeably quieter. The knocking sound on the cylinder is also gone, which I only noticed later. Since the adjustment, the values for the idle speed control are much closer together. I can't exactly say why everything is better now, but I'm happy with the results."

What is the alignment angle for your vehicle?

Mpire.

Mpire wrote:

Months later, out of curiosity, I adjusted the camshaft timing wheel. Beforehand, I read the correction angle. VCDS showed +0.3°, meaning the camshaft was set later. I then adjusted it to -0.5°, meaning earlier (VCDS always shows where you should be, not where you are). I was very surprised, but now it starts immediately even at -15°C, and runs smoothly without coughing or shaking. The fuel consumption has decreased by 0.3L, and it runs noticeably quieter. The knocking sound on the cylinder is also gone, which I only noticed later. Since the adjustment, the values for the idle speed control are much closer together.

Hello,

Thank you for the interesting story! Is the engine a 3-cylinder TDI?
Is the energy saving related to the battery charge indicator, or to the energy consumption during overnight charging?

Quote:

What is the correction angle for your vehicle?

The idle display is 0 to -0.5°, so according to the display, it's already slightly in the early range. However, depending on the (mounting) tolerances of the crankshaft position sensor, this may not mean much...
I'm planning to adjust the NW (North West) soon, but unfortunately, my gearbox doesn't have a TDC (Top Dead Center) viewing hole .

Quote:

I'm planning to adjust the NW (needle width) soon, but unfortunately, my gearbox doesn't have an OT (over-travel) viewing hole

.

You don't need that. Check the camshaft timing angle using VCDS, make a mark on the two-piece camshaft sprocket, loosen it, adjust it, tighten it, and then check the new timing angle using VCDS.

vwSchrauber wrote:

Check the camshaft timing angle using VCDS, make a mark on the two-piece camshaft wheel, loosen, adjust, tighten, and check the new timing angle using VCDS.

In principle, it's clear. However, the small available radius between the camshaft axis and the possible mark requires extremely precise observation when adjusting the timing... estimated at 0.3 mm for an adjustment accuracy of +/- 1° KW.
Well, let's see how I'm going to manage this.

The knocking sound could also be coming from the AGR valve. Try disconnecting the vacuum hose and plugging it, then listen to see if the sound changes.

Quote:

Thank you for the interesting story! Is the engine a 3-cylinder TDI? Is the fuel consumption reduction related to the BC display, or to the fuel consumption during overnight charging

?


Yes, it's a 3-cylinder TDI engine. The Lupo doesn't have a trip computer, so the fuel consumption was calculated purely based on refueling.
Regarding the inspection hole, I have one, but I also used the method from "VW-Schrauber," and it works quite well.
I then glued the dial of an old measuring instrument with a diameter of 60mm onto a magnetic film. This can now be glued in the center, between the three screws, onto the north-west screw. Make a small zero mark on the wheel beforehand, and it will be a great help when adjusting. There are probably better methods out there...


Best regards, Mpire.

Thank you for the praise, but the credit probably belongs more to VWSchrauber.

@"Deus Violentia"

Okay, you're right, I've corrected it .


Mpire.

Mpire wrote:

Months later, out of curiosity, I adjusted the camshaft timing. Before doing so, I read the correction angle. VCDS showed a value of +0.3°, meaning the camshaft was set later than it should have been. I then adjusted it to -0.5°, which means setting it earlier (VCDS shows you where you *should* be, not where you *are*). I was very surprised, but now it starts immediately even at -15°C, and runs smoothly without coughing or shaking. The fuel consumption has decreased by 0.3L, and it runs noticeably quieter. The "knocking" sound on the cylinder is also gone, which I only noticed later. Since the adjustment, the values for the idle speed control are much closer together.

I also adjusted the ignition timing on the BUK by about 2° KW earlier (without a viewing hole, using the smallest possible adjustment increments with my tools). Before, with a warm engine, it was at 0 to -0.5° (logged at approximately 24,000 km), now (at 37,000 km), at 28°C water temperature, it's at about 0.5°, which is a bit late.

I can only partially understand your successes, especially considering the initial cold start (water temperature = 2°C).
The acceleration to the LL speed was slightly more forceful than usual, with some hesitation (but not perfectly smooth), and the LLR log data showed relatively little variation.
However, the knocking sound doesn't seem to have become noticeably quieter (you're describing it as "nailing," which suggests a higher-pitched sound to me?), and I'm still getting LLR data during cold uphill acceleration that reaches the limits at +/- 3 mg.

However, the early NW adjustment will remain as is for now, because the displayed LL injection amount has not noticeably changed, and therefore the NW should not be in the extremely early range. Otherwise, based on the experiences of other test pilots, the LL consumption reading would increase.
I'm hoping for (mainly) a bit more responsiveness at higher RPMs, but I want to test that once the engine is fully up to operating temperature again.

Have you ever removed the AGR?

Deus Violentia wrote:

Have you ever disabled the AGR?

I always drive with the minimum AGR rate (adaptation). Trying it "completely off" doesn't make a significant difference anymore.

Hi,

Quote:

a little chip tuning (160 -> approximately 180 horsepower)

In that sense, I'm sure you've optimized your AGR, right?

RedR32 wrote:

Hi, Quote: a little chip tuning (160 -> about 180 hp) In that sense, it's definitely optimized, your EGR, right?

No, the EGR map is unchanged.


By the way, you can faintly hear the acceleration knocking in this video.
http://www.youtube.com/watch?v=gTcb2zKzsSM
... within a range of approximately 9 to 17 seconds, after which it gradually disappears into the general (idle!) engine noise.
However, it becomes very clear again when accelerating with the engine running at low RPM shortly after cold starts in freezing temperatures.