01 V70 Vacuum leak

Hi there !! My new (to me) V70 T5 has a hissing sound in the cabin, which I
suspect is a vacuum leak, took it to the dealer and they said that the brake
booster have to be replaced ($540 plus labor). I would like to plug the
vacuum line that feeds the booster and make sure that the diagnostics is
accurate/ Couple of questions:

- The vacuum feed for the AC vent actuators, where is that coming from?
- The vacuum hose that feeds the brake booster only feeds the brake booster,
and not any other vacuum reservoirs, right?

If this is a common failure, am I on the right track?

Thanks

Arnold

 

Engine vacuum.

Again from engine vacuum.

Usually the cause is some previous repair where the
mechanics brakes the hose when repairing anything else.
The less goings to the work shop the best.

Basically you need to locate where is the hissing sound
comming from. From the engine compartiment, or from
the interior of the car.

That's no vacuum pump, so that vacuum always comes
from the engine intake manifold.

 

Thanks for your reply, What I was asking was if the vacuum source for the AC
actuators and the brake booster are coming from 2 different places on the
intake manifold, so I could isolate the vacuum leak by plugging one hose at
the time in the engine compartment. I could not do that if they were fed by
the same point, and split with a Tee downstream, or if the actuators are fed
from the brake booster. The hissing sound appears to be coming from
an area under the steering wheel. I will not have access to the vehicle for
another 7 to 10 days.
Thanks

Arnold

 

Best chance that it is the brake booster very common complaint nothing
to rebuild just replace the brake booster. The noise will get worse @
some point & the power brake's will slowly start to get harder to press
Glenn

 

Look, vacuum is changing all the time.
You can have hard vacuum under heavy decceleration, and
no vacuum at all when the turbo is at full pressure.
So, the hissing sound must change accordingly.

Hissing sounds may have many sources.
You need to find the patern, when it changes sound, and so on.

Brakes is hard to believe - large independent hose with an
anti-return valve.
The AC actuators could be, but again vacuum changes all the
time inside the intake manifold.
There is a small vacuum hose for the turbo indicator too.

Are you sure it is a vacuum related problem?

If its a gasoline car, usually vacuum problems causes the
"engine failure" lamp to light (lambda sensor), due to
a faulty air intake.

 

Hi Mr. Albuquerque, you are correct, the hissing noise changes per driving
condition, under acceleration, or when climbing a hill, it is barely
perceptible, however, when the car idles, it is very noticeable. Have not
had the "Check engine light on" yet, maybe the computer tries to compensate
the mixture based on the O2 sensor, but I sure would like to eliminate the
leak and avoid running it like this. Thanks a lot for your help. Something
else I should check is if after I shut the car off, there is enough vacuum
in the brake booster reservoir to apply the brake once, if I can, then I
know for sure the leak is elsewhere because the check valve would hold the
vacuum in the brake booster.

 

If so, your vacuum hypotesis is quite good.
At idle you get a steady situation with a good vacuum to test
all the hypotesis of a leak.

So, its a small leak.
There are many small hoses hidden below the intake manifold, some
go down to the turbo.
The engine is very complicated to work with (very compact).

Check the turbo indicator hose that shoud go up to the
instruments pannel (I belive), since its a direct indicator of
the vacuum and could be itself the responsible.
And the AC actuators vacuum too.

Brakes system is all inside the engine compartement and most
certainly a small leak cannot be heard inside the car, since those
cars are very well sound isolated.