Some of you will have read my post about replacing the brake vacuum pump last week on my GT. All is well I am pleased to say.
However, the car seems to be running stronger since I fitted the new pump, so I have this question: Are the Turbo's affected by vacuum?
Over to you folks.

 

No, the turbo can't be affected by the brake vacuum pump.

it could, maybe, if the brake boosters used the vacuum generated from the manifold of the internal combustion engine. which is the case in a lot of cars. but it's an older technology.

in the Bentley is not possible since the brakes got their own dedicated vacuum pump.
what could have happen is that, since the pump was worn out, it was running almost permanently to do it's duty thus absorbing more energy than the new one.
but, frankly, I don't believe that the few HP the pump is using makes any difference... if it's the case and its using more HP than I believe you should see your mileage improve, slightly.

 

OK. Thanks for that. Must be my imagination playing tricks.

 

Hey if you think it is faster then it is.

Must be the case. After all I see the young folks with these four baggers adding a muffler to make it loud and a spoiler to keep the new beast of a car on the road.

 

Yes the turbos are affected by vacuum but I do not think you would notice with a vacuum pump replacement. The waste gates are vacuum controlled this vacuum is supplied by both the engine and the vacuum pump. The vacuum pumps purpose is to ensure adequate vacuum under all conditions (mostly while the intake has a positive charge from those little snails). The vacuum pump directly supplies the infamous "engine out hose" which runs directly above the steering rack. From that hose there are a series of slices and check valves for other vacuum control devices like the brake booster, waste gates, evap purge valve, and muffler flaps to name a few. I have not seen your other post so I'm not sure if the pump was dead or just noisy. I think its possible you would notice just not likely because if it were that bad I would think the car would notice and set a fault or you would notice other things such as brakes are more stiff or muffler flaps inop. Anything is possible. side note one of the major give aways that the major vacuum pipe has given out is waste gate control faults on both banks.

 

I stand corrected!
since you're a Bentley tech. you're surely much more competent than I'm.

anyway I'm surprised that the waste gate is is vacuum controlled by BOTH the engine and the vacuum pump is that only a redundant safety or there is other reasons?
I though that the only purpose of the vacuum pump was to ensure proper vacuum for the brake booster, for safety reason, and that all the others needs were taking care of by the engine.

since I'm going to pick up my car today, I'm interested to know if a noisy vacuum pump is the sign of one, or several hoses, are leaking or if it means that the pump is on the verge to break.

 

I hope it didn't come across that way. I wasn't looking to correct you because you were not entirely wrong. I was attempting to paint a better picture of how the vacuum system is laid out. I should clarify the wastegates are not completely controlled by vacuum. They just have the ability. Most of the time boost pressure is routed to the front side of the wastegate actuator. The higher the boost the more it pushes it open thus redirecting exhause flow Away from the turbo exhaust wheel. However vacuum is plummed to the back side of the wastegate for control if needed. Also the vacuum control isent redundant because the engine supplies the vacuum. When boost begins to build a check valve closes sealing in the vacuum. There is a sensor that monitors the supply. If you use the brakes or the supply drops the vacuum pump kicks on to top off the supply

 

Hi.
Thanks for the info'.
My story is this. The vacuum hose assembly on top of the gearbox was replaced last year after suffering a leak. Engine out job, etc. This was done by a main dealer.

A few weeks after, I took my car to an Indy for a service and a couple of other minor jobs.
My Indy mentioned at the time that the vacuum pump was noisy. It certainly was!
However, after driving away from the Indy garage the noise stopped but it didn't register with me. After a couple of weeks I remembered about the noise and investigated with my analyser. It turned out that the vacuum pump fuse had blown. I presume because the pump was burned out. The engine check lamp was not lit at any time before or after the fuse blew.
I then sourced an Audi A8 pump, same part number, and fitted it. All back to normal and that led me to ask about the performance, as it did feel better and yes, the brakes are better too. The exhaust flaps are disconnected by the way.

Thanks for the input.

I shall now pursue my new problem of the drivers door not locking with the touch button on the door handle. That was replaced just over 2 years ago by the main dealer so I am a bit annoyed.
Onwards and upwards!

Les.

 

Bit of an update.

After thinking that the car ran better after fitting the new vacuum pump it appeared that it shouldn't have made a difference.

However, I just noticed, thanks to the PDF fuse info supplied by PMS, that the blown fuse also supplies the Air flow meters, Exhaust gas sensors and the SAI control valves, whatever they are.
Maybe that helped it run better after all.

You learn something every day and thanks PMS.

Les.

 

hi - you are telling here about exhaust flaps.

what is their purpose.

why one should have them connected

why one should disconnect them

where is the place i can disconnect them / any fuse or smth?

 

In addition to all said I can tell you that vacuum does affect turbo and engine performance. Somewhere along the line someone broke both legs off the solenoid that is located near the engine oil fill. Look hard and you will see it with the pop off panel removed. Just follow the hard line that runs down the center of the engine.

Needless to say I had two BIG holes in the vacuum system.

The vacuum pump ran every time I touched the brakes and the engine ran like crap.

The car idled like it had a 'full race' cam with lots of misfires and it struggled under load going up a hill.
The vacuum system on the W12 is a real Achilles heel for the car.