actuator actions

[passat 130 tdi]

one or 3 questions for the gurus , when the turbo is working and boosting i take it the actuator arm is pulled down and then its upto the actuator to bring it back up . thus when the vanes stick the arm is jammed down and the actuator cant pull it back up . ????????????????? is this correct .


2nd question - does the n75 valve supply the vacuum pressure to control the actuator movement .


3rd question - boost control valve ??? - whats its purpose and is this located on top of the plastic section of the pipe at the rear of bulkhead righthand side . ??????

[martin1810]

When you start the engine The engines tandem pump produces the vacuum (sucks).

This vacuum (suction) is used to control four systems.
1. Brake servo
2. EGR valve N18
3. Intake manifold flap valve N239
4. MAP regulator valve N75

Vacuum passes through a one way valve to the brake servo to give assisted brakes.

Vacuum passes to the EGR valve The EGR valve controls the EGR actuator which moves a flap between the exhaust and intake manifolds and holds it open. The EGR valve can bleed vacuum to the air filter which lets it shut. An electrical impulse from the ECU also controls the bleed off and therefore the opening and closing.

Vacuum passes to the Intake manifold flap valve. Vacuum in the intake manifold flap valve regulator, acts on an actuator to pull the intake manifold flap open. When the engine stops, vacuum is lost and the flap valve closes.

Vacuum passes to the Map regulator N75. This allows vacuum to pass to the turbo actuator and pulls the actuator to actuate the turbo. (In the old days, more vacuum meant more turbo, this is not the case with variable vane turbo’s.)
The Map regulator N75 can bleed vacuum to the air filter. The Map regulator is electronically operated by the Map sensor via the ECU. The Map sensor detects excess boost pressure in the intake. An excessive boost pressure signal causes the ECU to send a signal to the Map N75 valve which opens and bleeds vacuum. This reduced vacuum reduces the pull on the turbo actuator and cuts turbo pressure.

The vacuum system contains THREE one way valves to help prevent failure of all four systems if a vacuum pipe leaks.

Need any more detail...let me know.

[passat 130 tdi]

thanks - sent you a pm , hope you can help me. :beerchug:

[passat 130 tdi]

Martin thanks for all your help , i just been out in this god damn snow and blew down the pipe leading to n75 valve with the engine off and it held no pressure at all , so i guess there is a split pipe somewhere or the n75 is U/S .

[martin1810]

Try again with the engine on.

[passat 130 tdi]

Will that still be ok as it is sucking with engine running , the air i put in will just go in anyways will it not . ?????????

[martin1810]

With the engine running, the pipe from the N75 to the air filter should not be sucking. It should only do that at very high revs when the ecu detects overboost and uses that pipe as a way of dumping vacuum.

[passat 130 tdi]

seems some wires got crossed lol - i was blowing down the pipe that goes to the actuator from the n75 valve .

i will try the air filter hose tomorrow now. :beerchug:

what should i expect to find blowing down that pipe with the engine running ????

[passat 130 tdi]

ok , i just used a small pump to blow down that pipe, with engine off it built up pressure and blew the pipe joint apart that goes to the egr valve . with engine running it also built up pressure but held steady ( no upper peak )

[martin1810]

The n75 acts a bit like a dump valve. Instead of dumping turbo pressure it dumps vacuum. So if the ecu is told by the MAP sensor that the turbo pressure is too high, it will open the N75 valve to allow vacuum to escape (let air in). With the engine running normally the pipe from the N75 valve to the air filter should be doing nothing because the valve is shut. This means that you can't blow down it. If you can blow down it, the valve is open and that is wrong.

[martin1810]

ok , i just used a small pump to blow down that pipe, with engine off it built up pressure and blew the pipe joint apart that goes to the egr valve . with engine running it also built up pressure but held steady ( no upper peak )

So the N75 valve is ok.

[passat 130 tdi]

id be better off doing this test after the fault occurs , is this correct???

[martin1810]

Probably not. You can try but I think that you have established that the N75 is working. If the MAP sensor is faulty it could tell the ecu lies and the ecu will open the N75 valve. So if it is open when in fault mode, it doesn't prove it is faulty....If you see what I mean.

[passat 130 tdi]

ok thanks , looks like im going to be busy , i may end up buying a new map sensor , n75 , replace the vacuum lines and clean the turbo vanes with that innotec turbo cleaner - if after then it still does this , im stuffed . :D the car did this before and was then fine for 2 months after i used that 10k boost spray from ********* - now its back again .

[martin1810]

I still think the most likely things is a vacuum leak. You could use your pump to pump up the system gently from the turbo actuator pipe end. The whole system should hold pressure. If it doesn't, you have a leak and need to find it. DO NOT PUMP UP TOO MUCH, just enough to get some pressure.

[passat 130 tdi]

i did blow down that pipe earlier with the pump and it didnt gain any pressure at all on the dial , with engine on and off .

[martin1810]

Were you blowing into the turbo actuator or back towards the N75 valve.

[passat 130 tdi]

back towards the n75 valve.

[martin1810]

So now you need to find the leak. That pipe should be air tight to prevent vacuum loss.

[cazyp]

Great thread Martin. I've never fully understood how this system works. Give me an old rover turbo anyday lol.

So to get it clear in my head, if I pull the pipe off the top of the actuator and blow into it with engine off it should hold pressure?
If not I assume the leak could be in 'any' of the following associated pipes?

Also where is the dump valve on this system?

Thanks :beerchug:

[passat 130 tdi]

seems related as the last job i did after my remap was to remove the n75 valve to clean up the terminals . maybe 1 of the pipes wasnt fitted quite right . i will take a look asap . thanks again martin .

[martin1810]

Looks like replacing the vacuum hoses will do it. Replace them one at a time so you can't make any mistakes on refitting.:D

[passat 130 tdi]

you can see by this pic is was quite a mess. guess im looking for a leak from the n75 pipes back to the actuator end ?

http://img.photobucket.com/albums/v417/maleborn1967/DSC00059.jpg

[passat 130 tdi]

well i took all the vac lines off along with the n75 and they all were ok, no leaks , i have my innotec cleaning kit ,which im attempting in the morning , if its still not right im guessing the n75 and thrust sensor will need changed, after that its the scrap yard for the old girl . :zx11: