VW Polo 1.4l TDI BMS - Acceleration Problems

Hello everyone

I have been experiencing an acceleration problem with my Polo for some time now (approximately 8 months).

Description of the error:

When the engine is cold, everything is fine. However, after about 10-15 minutes, the problems start to appear.

Acceleration in 1st - 3rd The connection is working fine.
Acceleration in the 4th and 5th Starting at a speed of 1500 upm, the engine starts to jerk and loses power around 1800 - 2000 upm.
The car also sounds like the exhaust is leaking and the turbo is blowing somewhere, which is causing a loss of power.

If this problem exists, I also cannot maintain a speed of 110 km/h in 5th gear. The engine continues to jerk. However, if I release the clutch and let the engine briefly idle before gently accelerating back up to 110 km/h, the engine runs smoothly and without jerking. -> Until the next acceleration.

When it started:
Last year, I had the brilliant idea to verschandeln the engine with a diesel additive. I have almost finished the liter and stopped using it when the shaking started.

What I have already done:

1. Replaced the valve for the boost pressure regulation.
2. Vacuum lines inspected (visually and checked for leaks using an air pump). After turning off the engine, it continues to maintain the boost pressure of the boost control system for a while before eventually "releasing" it.
3. Operation of the loading pressure control checked = Using a long-nose pliers, the rod with the hose is moved up and down smoothly.
4. Using VCDS, performed the valve-by-valve diagnosis for the AGR (Exhaust Gas Recirculation) and the turbocharger boost control. The change in the mbar reading is approximately 130-140mbar.
5. Pressure hose from turbo to AGR valve checked visually, I wanted to test this again under pressure, but I haven't done so yet.
6. The tandem pump's seals were replaced because there was also a relatively large amount of oil in that area.
7. Electric connection to the pump nozzle elements replaced.
8. The movement from the valve actuator to the pump nozzle: elements re-adjusted (lowest point on the pump nozzle -> turn screw on block -> loosen 180° -> tighten)
9. Load cell sensor calibrated using an external measuring device, to verify that the values are correct (using a calibrated differential pressure measuring device from the company).

I have a measurement in MWB 3-8-11 with an attachment, but I cannot determine what is causing the problem. The engine's RPM fluctuates noticeably.

Hello,

where in the log does the engine stutter? Does the engine get enough fuel, so that the fuel tank ventilation is okay and the diesel filter with its hoses are also okay?

Best regards, Rainer

Hello

The engine's RPM fluctuates somewhat, which is different from previous measurements that I occasionally took. For comparison, I have attached two screenshots: one showing a greater fluctuation in RPM, and one from a previous measurement without any issues. Both in 4th gear at full throttle.

Last week, I also bled the air from the system, from the turbocharger inlet all the way to the engine block. For this, I removed the turbo hose from the filter to the turbo, and attached a printed adapter to the turbo inlet.
Then, using the pressure reducer, gradually reduce the pressure to the system to 0.5 bar. It squeaks in a few places (2-3), but unfortunately, the construction wasn't good enough to really pinpoint the leak.
I want to construct another adapter here to find the leaks.
What pressure should the system generally be able to withstand?

In the logs, I can read a value of 2400 mbar. Is this a relative or absolute value?

Fuel lines are in order (visual inspection) in the engine compartment.
I had also suspected the diesel filter and replaced it with a new one, but I had forgotten about that.

Regarding ventilation: How can I best test it? I don't want to drive around with the fuel cap open.

If I'm assuming a boost pressure of around 1.0 bar, the system should be able to withstand twice that.

With 9N & Co, I've had multiple failures with the air-conditioning condensers.

Hello,

ok, the RPM drops also occur at low RPMs and, surprisingly, even improve at higher RPMs.
In the event of a diesel shortage (filter, tank ventilation), this would not be the case.

Does the backup pump provide enough pressure? Can it be measured, there should be something about it in the RLF?

"While the intake air might be leaking, the boost control and the limiting amounts are normal."

What are the idle time requirements and operating hours for the PD elements?

Best regards, Rainer

Hello

I haven't measured the pressure of the tandem pump yet, so I need to acquire some measuring equipment first.

What does RLF stand for?

I have already partially reviewed this post:
/viewtopic.php?t=3285

I was particularly drawn to this article:
Symptoms: Jerking / Stalling in PD motors under high load / full load

And your approach to this solution also caught your eye:
/viewtopic.php?t=161
Due to a lack of equipment to measure the pump pressure, I was unable to do so.

I have also included the idling speed control and operating times of the PD elements when the engine is cold and when the engine is warm (45 minutes/60 km commute to warm up).

Hi Florian

Hello,

Gilliearnie wrote:

What does RLF mean?

RLF = Original VW repair manual/workshop manual.

Many technical terms and abbreviations are listed and underlined in this forum, and they display an explanation when you hover your mouse over them
On the smartphone/tablet, highlighting seems to not be working...

Best regards, Richard

Hi

Yesterday, the device arrived, and today, after my commute home (after the engine is warm), I installed it once. Unfortunately, the correct adapters were not included in the set, which caused some leakage.

But even with the leaky adapter, I was able to read a pressure between 3.8-4.3 bar at idle.
Then I increased the RPM to 1500 upm (gently pressed the accelerator pedal) and immediately saw an increase to 7-8 bar (the needle moved strongly and erratically in this range).

I would now like to purchase another adapter and also check the pressure gauge once with compressed air and a calibrated measuring device.
Just to make sure I'm measuring the right values.

But I think the tandem pump provides enough pressure, and also the PDEs are not leaking, because otherwise the pump wouldn't have been able to achieve the pressure.

Can this possibly help:
Whenever the vibrations occur, it sounds like I'm driving without an exhaust muffler.

I now have the following theory:
1.
The tandem pump experiences very strong variations in vacuum, ranging from 2000upm, which causes the pressure limiting valve on the turbocharger to be controlled differently.

Is that possible?
If so, what is the differential pressure in this line so that I can find a suitable measuring device? (I have a Testo Smart Probe differential pressure measuring device that can measure from -150mbar - +150mbar)

2.
The exhaust hose is somewhere clogged and collapses as the pressure increases. (This sounds a bit strange, but in my head, it makes a little sense, even though I can't explain how it should work)

Perhaps there is a piece of metal somewhere that is reducing the cross-section, because it is facing the airflow and is bent inwards at high flow speeds. This narrows the cross-section.

But one would probably be able to see that in the boost pressure and the air mass, or?

Maybe someone still has a tip for where I can look further.
Are the two logs for the operating hours and the idle mode control the correct ones?

Thank you.
Hi

Is the PD cable harness an OE VW part or a cheap alternative?

Hello

The one that was just installed is probably a more affordable component.
There were also sealing strips and screws for the PD elements, and the total cost was 80€.

At AHW, the cable bundle costs 90€. If I had seen it before, I would have bought it immediately.

Hi

To ensure that the problem wasn't due to cheap parts, I would install an OE PD cable.

Has the diesel filter been replaced before? In my A2 TDI with AMF engine, the cause of the jerking and stalling was the old diesel filter. I found a solution in the A2 Freunde forum: a new Bosch filter and everything is now working perfectly.

{LOCATION} is located directly under the chassis, near the fuel tank. Could this be the cause of the phenomenon?

Hi everyone

I have found the error, thank you for the helpful advice and suggestions.

To Error:
I have re-examined the problem statement from the Dieselschrauber perspective and have looked at the timing and quantity discrepancies in the specific case.
In cylinder 3, the timing deviation exceeded -128. Then also put the other two cylinders in the higher minus range (between -20 to -115).
After some research online, I found a post where someone mentioned that the return flow ports in the PDEs might be clogged, and/or the seals of the PDEs might be clogged.

I then decided to try the PDEs . (It went surprisingly smoothly and easily)
You can see the results on the images, where two out of the three PDEs had seals in place.

I then replaced the seals (three O-rings), the brass disc, and the plunger (is that what it's called?).
Then, using a brass brush, I carefully cleaned the nozzles of the grime and then reassembled everything, lightly lubricating it with motor oil.
After a while, the engine finally started, and the measurements showed values for all three cylinders between -22 and -64.

The car is running smoothly again, without any jerks or problems.
I think I'll still replace the diesel filter, because the deviations aren't moving in the right direction.

Lg from the sunny north