I have noticed that my vacuum pump starts as soon as I touch the brakes.
it works for 15/20'' and stop.
as soon as I depress the brake pedal it starts again...and stop!
otherwise the car has no problem, no rough idle, no engine light warning.

I guess that it is not a case of the infamous ''vacuum leak-engine out'' since if it was a leak the pump should run permanently.

any ideas?

 

I agree. If the pump stops, vacuum is achieved. My 2005 does the same as yours. Three independent smoke tests on my Conti show no vacuum leaks.

 

OK then, the ''vacuum leak'' issue being cleared by PMS, thank you for that, did you found a solution ?

I understand that the vacuum pump should not start EVERY TIME you touch the brake pedal so...something is wrong somewhere.

a faulty vacuum pump?

 

I believe the pump is demand-driven. If the demand is low and the reservoir is full, the pump won't activate. You can only hear the pump at idle (when the demand is high). Once you are on the road, you can't tell if the pump is working because you can't hear it. Since you don't report any DTCs and the car is performing normally, I don't think you have a problem. If you are in doubt, run the car through a VAS5054A diagnostic session or do a smoke test. There are a number of videos available on the proper way to perform the smoke test.

 

thanks for your reply.
in fact the pump starts every time I touch the break pedal an I can hear it when it starts even if I am on the road.
as I said it last a few seconds, 10/25, an then it stops and start again when I touch the pedal.

 

Hi Ulstrup.

Sounds like a leak to me.
I recall my Indy mechanic saying that you should be able to depress the brake pedal a few times before the pump kicks in.
Do you have any good Indy's in you homeland? I certainly would be apprehensive about trusting it to a French outfit.

Good luck.

Les.

 

Hi Les,

yes, that was my first reaction.
but if it was a leak the pump should run permanently and as per most of the others, including you I guess, I should have warning lights and a rough ride.

I'm going to perform a smoke test and find out.

well, in my homeland, Denmark, I have 1 bentley dealer and there must be 20 CGT/CGTC in the whole country!! don't forget that if you're a Danish resident you have to add 280% luxury taxes on the net price and then 25% VAT!!! so the final price for a new GTC is close to 600k€.....

expensive little toy, indeed.
so, the dealer up there is a joke and an expensive one .

the dealer down here is based in Monaco with a sales subsidiary in Cannes.
entering the garage will cost you 500€ and shaking hands with the chief mechanic another 1000€. on top of that they are totally, I mean totally, incompetent.

a British friend of mine found a very good indy specialized in Jaguar/Bentley/RR close to Cannes; my car is maintained by these guys and I'm very happy with them.
the smoke test will be done by them next week.

 

Hi Ulstrup.

That's why mine always goes to the Indy guy in Crewe.
Good luck with the smoke test.

Les.

 

ULSTRUP,

did you complete the smoke test ? What was the result as I have the same exact issue as you.

Thank YOu

 

edinp,
No I didn't. the car runs perfectly and I don't want to get the engine out until I have a real problem.
if its a leak, the leak must be very very small since the pump runs no longer than 10/20 seconds and then stop and doesn't start again until I use the brakes again.

what is surprising is that I drive mostly on highways were you don't use the brakes often, IF it was a leak, even a small one, the pump should start from time to time and it doesn't....
my indy says that he has never seen that so, my decision is ''wait and see''.

 

Got it. Thanks Ulstrup.

 

....9 months later does the pump mystery persist...if you please restate the exact current condition, I will do further research...Hello From San Francisco...JimB

 

I still have the same issue on my 2005 GT. Every single time I touch the break pad, the pump goes on for 10-15 seconds and then goes off. Other than that, I have no other issues.

 

I have brand new metal lines and it works as you described..

 

Hi BentleyF,

thanks for getting back. It sounds then like it's a different issue and not an issue with the vacuum leak. Some mechanics went as far to say "it's a known and ignore-able issue with that car".