I have a 19 Cayenne 82k miles with the 2.9 bi-turbo in the shop. Smoke test comes out fine, no leaks. Bypass valves are working and not leaking boost. Brand new N75. 20" of vacuum to N75. Duty cycle at the N75 is 23%. Waste gates are resting on the full open stop when idling. If I apply ground to N75, the wastegates close as expected. When I rev engine, 100% throttle and then let off at 3k is rpm, duty cycle from ECM will rise to 50% and then go back to 23%. No boost at all in any gear. I can't find any adaptions or basic settings for the wastegates or N75. It does pass the wastegate/N75 test.

Water pump failed 8 months ago, I replaced it, blew out all the vacuum lines with soap and water, and replaced the N75. Truck was perfect for 8 months.

Could it be that the N75 I replaced 8 months ago failed and caused an overboost situation until the ECU adapted to 23%? Do I need more than 20" of vacuum at the N75? Is there a way to clear or is there even adaptions for the N75?


Thanks,
Chris

 

Check both wastegate actuators with a manual vacuum pump on the vacuum capsule. Maybe you have a wastegate lever on its way to failure (breakage) or wastegate rod bearings getting sticky on their way to seizing.

I have not seen the spec for idle vacuum level in bar. You believe your vac lump, reservoir and lines are good, correct?

 

Fixed it after 2 days of pulling my hair out. I was getting 20" of vacuum at the N75, so I went and measured the vacuum at the vacuum pump and it was 20". I pulled the one way valve out of the charge pipe, I stuck my finger over it and the vacuum went to 30" The one way valve in the charge pipe had a tiny speck of something in it and was allowing the vacuum pump to pull air out of the charge pipe, stopping the vacuum pump from pulling 30" on the brake booster, water pump, and N75.

So yeah, the N75 needs to have 30" of vacuum to it in order for it to correctly control the wastegates.