AKAvant
Veteran Member
- Joined
- Oct 12, 2010
- Location
- Europe
- TDI
- 2004 Audi A4 Avant 1.9TDI Quattro, 2002 VW California, 1998 Jetta TDI (Sold 6/16), 1997 B4 Passat TDI, 1993 Eurovan Weekender 1Z m-TDI conversion (Sold 5/12), 1992 AHU powered B3 Syncro Wagon
The car is a 2007 Audi A4 with the 140hp 2.0tdi engine code BPW. I’ve been chasing an intermittent low/fluctuating boost issue for some time now. All vacuum lines have been changed along with a new MAF and N75 and I have properly adjusted the actuator arm which moves freely. Vacuum stays constant with no leaks with engine off. The issue occurs more often at low rpm driving in stop and go traffic and after long descents while using the brakes. This results in underboost followed by overboost, but if I rev and push the car hard thru a few gears the actual boost starts matching the requested almost perfectly. I placed a vac gauge directly to the nipple from the hard line from the vacuum pump while at idle and pressed and held the brake pedal repeatedly. The vacuum initially climbs somewhat slowly to 20Hg and then even slower to 25 and creeps to around 27. The needle also shakes as it climbs. When the brake pedal is pressed vacuum drops quickly and when held vacuum drops close to zero. The pedal also gets hard then. Is this normal or indicative of a weak pump or issue with the brake booster? The video shows the vacuum gauge when I press the brake pedal. The car has 293,000km on it. Thanks for any input
https://youtu.be/0yxKF553mkg
https://youtu.be/0yxKF553mkg