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Still working on powerless acv. I can't see where anyone has posted the piping layout for the valve switch.
Which pipe replaces where the mini air cleaner pipe goes on to the n75 is it the Pipe from the turbo supply pipe or the one that goes onto the end of the crank case breather.

Also there is no vacuum pipe going into my ecu at all. Are some acv's meant to be this way or have I a pipe missing .

Cheers for any help.
 

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try this link
It shows the two types of vac valve found on the ACV engine. The flatter square one is the N75, and the one towards the bottom of the original post (which is listed as the N75 for AHY engines) is the N18 (on your engine).
Follow the diagram to the letter.
 

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try this link
It shows the two types of vac valve found on the ACV engine. The flatter square one is the N75, and the one towards the bottom of the original post (which is listed as the N75 for AHY engines) is the N18 (on your engine).
Follow the diagram to the letter.
Doesn't quite work like that. The EGR solenoid on ACV/AJT is a vacuum valve, the N75 is a pressure valve. AHY engines have a variable vane turbo which is vacuum controlled and that is why it uses the same solenoid as EGR.

However, on an AJT/ACV engine the turbo is pressure regulated/controlled via the wastegate. If you put boost pressure through a vacuum valve it will leak and hence not prove whether your N75 valve is faulty.
 

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Well it has been working for me for half a year, and dosent throw any fault codes up on vagcom. You need to swap the electrical plugs over too.

I thought both valves were effectively comparator valves, The N75 compares inlet and boost pressure from the turbo, and uses this to control the wastage (with help from the ECU) whereas the N18 valve effectively compares vacuum pressure with ambient pressure and the ECU diverts the vacuum to the EGR control valve when needed. This only applies to the ACV engine, not the AHY.

I was only using the AHY diagram to illustrate how to rig the N18 on an ACV to do the job of an N75, because the valves look the same physically.

The differential pressure between the relevant inputs/outputs on the N75 and the N18 will be almost the same on the ACV. N75 compares inlet to boost, which is around 15psi (or thereabouts), N18 compares air pressure (around 15psi dependent on altitude) to vacuum (0psi ideally) which is around 15psi. The N75 plug will fit the N18 valve and the ECU will then treat it the same as the N75.

Surely any vacuum valve is a pressure valve, ad vacuum is simply negative pressure and creating a vaccume will invariably result in pressure being exherted on the area under vacuum, remember Newtons second law of motion.
 

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I thought both valves were effectively comparator valves, The N75 compares inlet and boost pressure from the turbo, and uses this to control the wastage (with help from the ECU) whereas the N18 valve effectively compares vacuum pressure with ambient pressure and the ECU diverts the vacuum to the EGR control valve when needed. This only applies to the ACV engine, not the AHY.
The solenoids are dumb - they can't do any 'comparison'. The ECU simply modulates the boost on an ACV/AJT (by PWM), AHY is similar by it is done by vacuum because the necessary boost pressure is not there at lower RPM. The pressure valve (N75) will seal differently and has a quicker step-response than vacuum. A vacuum valve will probably work but it will leak - have you ever wondered why there are two different valves if one type will do both jobs?

I was only using the AHY diagram to illustrate how to rig the N18 on an ACV to do the job of an N75, because the valves look the same physically.
It is the same solenoid because AHY has vacuum controlled VNT. Otherwise Bosch (who designed the engine control) would have fitted two of the same valve.

The differential pressure between the relevant inputs/outputs on the N75 and the N18 will be almost the same on the ACV. N75 compares inlet to boost, which is around 15psi (or thereabouts), N18 compares air pressure (around 15psi dependent on altitude) to vacuum (0psi ideally) which is around 15psi. The N75 plug will fit the N18 valve and the ECU will then treat it the same as the N75.
Like I said it doesn't quite work like this. Firstly the valve doesn't 'measure' any pressure differential. N75 doesn't 'compare' anything - it is simply modulated by the ECU. Both plugs will fit and the ECU will not flag a fault because both solenoids have similar electrical characteristics. It won't 'treat' it any differently if you were to plug a dummy inductive load in there either.

Surely any vacuum valve is a pressure valve, ad vacuum is simply negative pressure and creating a vaccume will invariably result in pressure being exherted on the area under vacuum, remember Newtons second law of motion.
Yes but the internal design is such that the spring forcing the seal/cup closed is in the opposite direction to that of a pressure valve and that is why it will leak - although it will probably work to a fashion. This is why (as I said earlier) Bosch didn't use two of the same vacuum valves instead of two different ones - pressure (boost control) and vacuum (EGR) on ACV/AJT.
 
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