Low rail pressure. - Defective high-pressure pump?

Hello everyone,

Our VW EOS 2.0 TFSI is acting up a bit, and when I read the error codes, I get the following:

00135 - Fuel System (Bank 1) - Fuel Rail/System Pressure Too Low.
P0087 - 002 - Intermittent.

I have now completed an extensive test drive, as we sometimes observed a brief power reduction during normal driving in certain situations. The test drive revealed that the target rail pressure drops for a few seconds under specific conditions. This occurs reproducibly when the accelerator pedal is fully depressed, the throttle is completely open, the engine load is very high (greater than 140%), and the engine speed is above approximately 3200 RPM. As soon as the load is reduced, the target and actual rail pressures equalize. If all these conditions are not met, the maximum rail pressure of 110 bar is maintained without any issues. The low-pressure pump provides a stable pressure of at least 5 bar.
"During normal driving, you don't notice these drops in power. I recently replaced the spark plugs. During the test drive, there was also an instance where, at full throttle, it took a relatively long time to build up power. Then, suddenly, everything was fine again." Sounds, etc. are not present.
I have the following questions:
1) Why can the motor load be greater than 100%? What does that mean?
2) Is there anything else I can check? Measurement run with additional data?
3) Could it be that the high-pressure pump has failed? Would you recommend replacing the pump?

I have attached the measurement data as an Excel file. The points where the rail pressure briefly dropped are highlighted in yellow. The points where there was no acceleration despite the pedal position are highlighted in red. Acceleration and Delta Rail were calculated, not measured.

Thank you for your feedback and input.

Hi.

1) The load factor can be greater than 100%, and it doesn't necessarily correspond to a load as one might expect from a range of 0-100%.
Regarding point 2: The pressure regulating valve may be faulty. You might see "jumps" in the actual pressure while the set pressure remains constant when logging the data. Edit: The areas you highlighted in yellow are suspicious. Since the pump is generally capable of reaching the necessary pressure, I would start troubleshooting the pressure regulating valve. Are the wiring and connectors for the pressure sensor/control valve okay?
Regarding point 3), if I recall correctly, the high-pressure pump/piston is a known weak point, so I wouldn't rule it out.

Best regards, Rainer.

The positive crankcase ventilation (PCV) valve was defective and I recently replaced it, so it's okay now. A test (removing the oil filler cap) has now confirmed this as well.

I've searched online again, and it appears that for diesel high-pressure pumps, deviations (target vs. actual) in rail pressure of up to approximately 10% are considered acceptable. In the measurement file, there are no other situations besides those previously described where there is a rail pressure difference of this magnitude. This means that the target and actual rail pressures are in good agreement. As previously described, the pressure only drops briefly when...

1. Strong acceleration is achieved (accelerator pedal at a minimum of 99%, throttle valve at a minimum of 95%).
2. Revolutions per minute (RPM) from approximately 3000.
3. The injection time is greater than 5 ms.

Regarding the pressure sensor: It seems the pressure sensor is prone to failure. When it fails, the engine should have difficulty starting or simply stall while driving. However, our EOS doesn't exhibit these problems. Furthermore, why does the sensor otherwise always provide plausible readings, except in the situations described? Could it possibly still be a problem with the sensor?

Besides a faulty HDP (High-Pressure Direct Injection pump), the fuel filter might also be the problem. Could a clogged fuel filter also cause insufficient fuel delivery, even if the fuel pressure regulator is providing the correct pressure?

Hi,

It's not uncommon for values on electrical sensors to fluctuate when there's a defect, but it wouldn't rule out issues with connectors or wiring harnesses (especially chafing).

With a clogged fuel filter, I would have expected a gradually increasing pressure difference in the fuel rail as fuel consumption increased, rather than sudden jumps. I don't have any experience with that type of engine.

Best regards, Rainer.

Evening.

I've encountered this issue several times with common rail systems where a slightly dirty fuel filter caused problems with the rail pressure.

Filters are also often neglected .