A2 1.4 TDI, 75Hp limp mode no turbo

zago

zago

Member
Hi,

Have a problem with the car so decided to ask for support. Looks like my turbo actuator doesn't work as there is no pressure from "black box" (box in picture No.18).
As there is no pressure turbine actuator doesnt work. From the vaccum pump to this box vacuum is about 1psi.
No faults on ECU present.
EGR valve looks like works ok. ?(opens/closes)
Turbine actuator activated if you give approx 1psi. from external resource.
Turbine cartridge changed to new one (worst nightmare in my life).

Does anybody knows how exactly this box works? How the pressure is created? how to test it properly or maybe anybody had similar issue?.


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Catnip64 said:
I assume you have a TDI 90 rather than a 75?
Have a look at this document: http://www.volkspage.net/technik/ssp/ssp/SSP_223.pdf
Page 61 suggests that the control module uses a vacuum signal to control the turbo vanes rather than pressure. My first port of call would be the N75 valve.
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My audi 2004, so I have this black box that works instead of N75 together with another valve. As far as I understood two valves was integrated in this one.
 
Ok so it looks like you have a BHC 75? Firstly have a full VCDS scan done on the car to see what the car thinks is wrong.

It is important to determine if the boost is being lost be a failed intercooler rather than turbo control issue. You will also want to physically check the end caps on the intercooler to see if the lower one has cracked / split and blown out the seal. It is also important that all the air pipes from the turbo, through the intercooler and into the inlet manifold are correctly fitted and without any leaks.

At the age of your car you may well find that the small braided vacuum and pressure lines that are routed to and from the turbo and the control block may be loose, disconnected, porous or deteriorated by oil contamination. Cheap to replace the lot. Then there is the possibility that some of the pipes entering the control block may be blocked or loose..........
 
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Does anyone knows what pressure from vacuum pump must be ? I mean that goes to black box. Looked at some videos and in vw is above 25 and i have only 1psi.
 
Today made few circles around my garage and fault occured (in picture)
Small hoses looks ok. So maybe that blackbox is a problem. Ill try to find one used.
 

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Looked everything for possible leaks but couldn't find anything. In some posts here found that under this fault can be intake pressure sensor (located on intercooler top) example FAE15037
 
Well worth replacing hoses with silicone ones, cheap upgrade, you won't notice the small splits in original hoses that cause issues with your eye.
I don't know what pressure the system uses.
Are you sure the pipes are connect to correct outputs of the valve? You should feel the suction for the turbo when building revs. On an atl variable the suction increases.
When the turbo was changed on mine some muppet put the actuator pipe onto a blank on the n75 unit
 
I''ll check some more data on intake manifold pressure. I have checked on idle only approx 850rpm.
According to information on 3000rpm must be 1375...1625mbar
 
Under the load is a different story. Not good.
 

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MAybe the vaccuum from the tandem pump isnt right, have you checked the outlet pipefrom the tandem? Is tandem faulty perhaps? good luck sorting it. I replaced all my vacuum pipes for silcone for £25, well worth doing it.
 
CrispyEdd said:
MAybe the vaccuum from the tandem pump isnt right, have you checked the outlet pipefrom the tandem? Is tandem faulty perhaps? good luck sorting it. I replaced all my vacuum pipes for silcone for £25, well worth doing it.
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Checked it is about 1psi. No clue how much should be.
 
Looking at other VAG forums the n75 runs at 20hg ish which is 10-12 psi? SO leak at brake booster or the tandem ump is guff or the pipe from the tandem pump is split
 
This is a good question.
In manual is 3.5 but measuring is in general pump. Who knows how much exactly it goes to vacuum solendoid.
image.jpg
 
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