Kniffelaufgabe: Ursachen für unrunden PD-BUK-Kaltstart? | Posts 192+

Hello Ulf, so I had obtained a readily available pressure gauge with glycerin damping at that time, and subsequently had the clocks serviced. However, I didn't personally test them using the connection screw that was supplied.
At low speeds, the pump tip pressure and resonances in the air-filled damper hose can interfere with performance. I will make you a different screw that has only a small 1 mm hole; this should improve the readings.
You can also fill the hose with oil before screwing it on (hold the hose downwards so that the oil doesn't leak out). The other screw had a thinner hole drilled in it, which might have made the difference less noticeable.
Certainly, a more expensive and twice as large glycerin-filled pressure gauge would provide a better reading. However, this one will suffice for now, especially if it shows a more stable reading when adjusted with the other screw. My concern was whether there was enough pressure at higher speeds.
Best regards,

Deus Violentia wrote:

Why don't you replace the tandem pump...?

Hmm... what would you expect as a result?

"No, leave the pump alone. Repeat the measurement using a different or modified measuring device. I agree with Klaus. Until then, disregard the readings you've already taken. Was the engine fully warmed up during this measurement?"

I've been using LL2 0W30 oil in my Sharan for a few weeks now, as announced, and it has noticeably improved. Attached are two of the usual start-up logs. In the first one, with the old 50501 oil, it was rumbling quite a bit, while in the second one, it was barely noticeable. The fuel consumption is also about half as much. I did one here in front of my door and the other a few days later on vacation at the Baltic Sea because I was afraid it wouldn't get cold again so quickly. The starting conditions and ambient conditions were kept as similar as possible. The outside temperature was -2.5°C according to the dashboard. The engine was cooled overnight and not preheated. It was glowed once, and the tank was full (the fuel pump didn't have to release any air).
In my opinion, it runs noticeably better with the thinner oil. The overall impression is also more harmonious and smoother. I've driven about 1500 km so far, and the oil level hasn't dropped. If that doesn't change, I will probably stick with this type of oil for the car. It's unlikely to be related to the salty air.

Steffen W wrote:

No, leave the pump alone. Do the measurement again with a different or modified measuring device.

One where the needle stays more stable?

Quote:

I agree with Klaus on that. Until then, also forget the values you read. Was the engine warm during this measurement?

No, it was cold. Because the problems only occurred when the engine was cold.

Okay, I think the cause of the erratic readings is likely in the measuring device itself, not in the vehicle. I once built a similar device myself, and this situation seems very familiar to me.
Let's see what readings he gets when the pressure gauge is modified.

Steffen W wrote:

Yes, I think the cause of the needle fluctuations should be sought in the measuring instrument itself, not in the vehicle.

Well, the pressure pulsations are certainly not invented by the gauge; they come from the engine.
I initially don't suspect a defect related to the engine itself, but rather the normal "idle pump strokes" of the high-pressure injection system that flow into the supply line – and that's where the measurement connection is located.

Let's see if I can arrange to do a comparative measurement on the ASZ Polo sometime soon...

The needle on this pressure gauge usually stays relatively stable, making it easy to read. In any case, your supply pressure is sufficient for now. That's what we were trying to clarify. Here are my experiences with this device:
/viewtopic.php?t=19461

Steffen W wrote:

The needle on this pressure gauge usually stays relatively stable, making it easy to read. In any case, your supply pressure is sufficient for now. And that's what we were trying to clarify. Here are my experiences with this device: /viewtopic.php?t=19461

Ah yes, so the needle also flickered during your measurements:

Quote:

I just measured the pressure of the tandem pump: It shows 3 bar at idle, and the needle fluctuates slightly by about half a bar. At 1500 RPM (engine cold), the needle jumps wildly between 3 and 8 bar. Can anyone tell me something about this? Does the engine need to be warm? Should I perhaps use a different pressure gauge with glycerin filling? Am I doing something wrong? Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. It was the pressure gauge. Today, I installed one from a well-known manufacturer with a glycerin filling, and it provided clear readings. 3 bar at idle (820 RPM in my case). 6 bar at 2000 RPM. and 9 bar at 4000 RPM

.
When I take the approximate average values from my readings (as mentioned above), I believe that fuel pressure can be ruled out as a cause of the problem in about 99% of cases.

ulf wrote:

If I take the approximate average values of the fluctuations during my readings, (as mentioned above), then, in my opinion, fuel pressure can be ruled out as a cause in approximately 99% of cases.

Steffen W wrote:

Your initial pre-pressure is definitely sufficient. And that's what this clarification was about, anyway.

I'm telling you.

ulf wrote:

Ah yes, so the needle was also jumping during your measurements:

There's also information in the linked thread about what can be done to fix the issue. I just wanted to prevent you from buying and installing a new tandem pump unnecessarily.

ulf wrote:

Steffen W wrote: Pressure gauge with glycerin filling, perhaps? Am I doing something wrong? Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. It was the pressure gauge. Today, I installed one from a well-known manufacturer with a glycerin filling, and it provided clear readings. 3 bar at idle (820 RPM in my case). 6 bar at 2000 RPM. and 9 bar at 4000 RPM . If I take the approximate average values of the fluctuations during my readings, (as mentioned above), then, in my opinion, fuel pressure can be ruled out as a cause in approximately 99% of cases.

Hi Ullf, as I mentioned before, seal the screw hole with two-component adhesive and create a small 1mm hole. It won't cost anything, and the pressure gauge will still show a stable reading.
Nevertheless, the pressure is probably sufficient for the pump to operate correctly.

Steffen W wrote:

I just wanted to prevent you from buying and installing a new tandem pump for no reason at all.

That's very kind of you .

teileklaus wrote:

Hello Ullf, as I already posted, seal the screw hole with two-component adhesive and make a 1 mm hole in it; it won't cost anything, and the pressure gauge will show a sufficiently stable reading.

I'll see what I can use to reduce the size of the screw hole.
Do you happen to know the inner diameter of the hose? Its volume is important for determining the appropriate clamping diameter.

Hey, you're not actually going to calculate the air volume inside the hose, are you?
"Daniel Düsentrieb"

And what if a part is full of diesel fuel?
Okay, I'll take a look.

The outer diameter of the high-pressure hose (NBR) is approximately 13.x mm; it's labeled as "/8x14-3" and should be 8 mm.
Outer diameter: 14 mm.
inner diameter: 8 mm
Each wall is 3 mm thick, resulting in a total thickness of 8 + 6 = 14 mm.
With a hose length of 100 mm, the total length is 5024 mm, plus the volume of the pressure gauge connector and the holes for the screws – now what?