Hello everyone,
I have now spent approximately 12 hours troubleshooting a 2.0 TDI engine with the following engine code: BKD.
Main Issue: Charging Pressure - Exceeds Limit
Pressure exceeds 2601 mbar, therefore, continuous emergency mode.
Error occurs only during uphill driving and overtaking maneuvers -> High load - requires full charging pressure for a long time.
AB is hardly/not used, only on country roads.
It's a 16V without a particulate filter.
Particle accelerator by Garrett: 1749VA
Mileage: 200,000 km Year of manufacture: 2005.
Here's the history:
Problem: Turbo makes a noticeably loud noise.
Idea: Engine damage (at the turbo), but first, research. Result -> Replace AGR pipe.
Work: AGR pipe replaced, part number: 03G 131 521 T
Result: Whistle remains unchanged. The old pipe seemed slightly leaky, but the subsequent leak test did not confirm this! Apparently still in good condition after 200,000 km.
Idea: Replace the turbo with a used one from another vehicle (1749VA)
Work: Turbo replaced, no more whistling!
Problem 1: Whistling reappears after 2 weeks
Problem 2: Also Notlauf aufgrund von Überhöhter Ladedruck über den Sensorbereich hinaus > 2601 mbar absolut.
Now began the extensive troubleshooting process, with the following information known:
VTG very smooth, the used loader was cleaned by me on the exhaust side and worked perfectly.
Pressure vessel was checked for leaks, using a vacuum pump with a manometer. This remained at -0.7 bar constant after 30 seconds -> Membrane is OK.
See my video in the attachment, where I re-tested the function in its built-in state today to ensure 100% certainty!
Idea: N75 could be nearing its end with 200,000 km.
Work: Replacement of the old valve block: 6Q0906625 with: 6Q0906625E. See picture!
Problem 1 & 2: Unchanged, Emergency shutdown if absolute pressure > 2601 mbar
Idea: Replace the hose from the valve (6Q0906625) to the air filter (check for continuity of atmospheric pressure, as this re-pressurizes the turbocharger's pressure chamber).
Work: Hoses inspected for blockage and proper function of the nipple in the intake area.
Result: No findings, it is obvious that the hose is in perfect condition.
Idea: Research revealed that the hoses connecting to the pressure cylinder can become softer at points of stress (own HYPOTHESIS!!), and therefore contract, preventing the vacuum in the pressure cylinder from being released.
Work: Replacing the hose from the valve block to the pressure cylinder (it's a real pain when there's no space anywhere...) (QUERMOTOR)
Note: I was too lazy to shorten the (universal) hose to 2.5 meters, what if it's actually not defective? That's just a matter of opinion.
Note: The original (DRECKSSCHLAUCH) has 2 nipples in between and is actually made of 3 pieces of air flow (from my mouth), which was also quite poor
... Quality product, you can find it at G******? No wonder that when you read online, you see that the first VNT TDI's, like AFN, have faster wear rates...
Result: Error remains unchanged initially.
Work 1: Because I was increasingly unsure about the VTG, I made a VTG video in this step to check it while it was in its built-up state.
Work 2: Okay, I'll shorten the hose and bring a T-piece with a pressure gauge for the charge. This also indicates negative pressure during test runs.
Result: No more errors... it regulates the target pressure and no longer shoots beyond > 2601 mbar absolute.
Solution: The hose collapsed at some point due to low pressure, so the hose to the low-pressure port was not of particularly high quality, and if it was/should be ventilated from the N75 above, it was likely still being pinched by the low-pressure reservoir in the pressure port, which caused the turbo to have a permanent and very high boost pressure, which created an unnatural boost pressure. (not measured with the LDA, but only familiar with the measurement blocks)
Note: I still have a slight lingering feeling that the error was still present with very long hoses. The hose was exactly the same length (I had used the cut piece perfectly for the LDA) thanks to the T-connector and LDA, but then the error (suddenly) disappeared.
Appendix:
Video VTG with vacuum hand pump
Image Vent Block incl. N75 Old & New
Log 1: I have a log showing that the turbocharger builds up to 2601 mbar (Nirvana) until the engine goes into emergency mode, and then there is a second attempt after the engine is restarted.
Log2: Now, during the test drive, I had just disconnected the LDA, and it was no longer going into limp mode, but only experiencing short-term overshoots, and not the long-lasting 2601 issue.
I will provide updates on the situation in the coming weeks. Suggestions and further questions are welcome. I hope my experiences help others in troubleshooting.
The vehicle is not mine, so the flow of information about the current situation, whether further errors occur or not, will be slower.
Best regards from Lower Franconia, your apple juice
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