Vacuum Pump Performance

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
 

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
It’s the original tandem pump, so a little over 293,000km.
 

pdtdiarl

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Joined
May 8, 2018
Location
EU
TDI
golf4
Some say life expectancy of a tandem pump is 250k kms.

I'm kind of dealing with the same problem my self, PD150, sometimes it lags, but on vcds vnt test, it moves correctly. It's my daily and hadn't time to diagnose yet.

You could also have a problem on the brake booster, some leak, try to plug the gauge directly to the tandem pump.
 

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 point I tested is almost right at the pump. I’ll try and check the booster hose fittings for leaks as well.
But do the readings from the pump seem correct? They seem somewhat weak, I feel like the vacuum should stay more level even when the brakes are applied.
 

pdtdiarl

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May 8, 2018
Location
EU
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golf4
Not sure what number are supposed to be in the readings, but since it's a pump and not vacuum operated like a NA gasser, should be quick to gain vacuum.
 

AKAvant

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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
I drove down a long hill today and kept the engine in gear at around 1800-2000rpm. Speeds were around 40km/hr and the final portion lasted a few minutes. I performed a test where I pushed the brake pedal about 4 times and then held it until I stopped. At the end the pedal was hard and I had almost no stopping power. I’ll recheck the brake booster hoses again but vacuum is maintained for an extended period of time after the car is shut off. The vacuum pump seemingly should be able to maintain vacuum in this situation?
 

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
Understand, thanks! But could a weak tandem pump also potentially cause this issue?
 
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