N75 / N18 help

I have a 1z / ahu swapped in a toyota

I swapped the n18 valve in for the n75 because I need vacuum to pull the turbo wastegate open.

If I simulated 10-30 lbs of boost to the ecu my n75 / boost valve duty cycle does not change nor does the wastegate move

Did I make a wiring mistake?

How to I get the n18 to open the wastegate?

How many pounds of boost does the ecu need to read before it opens the wastegate?

If you really have bacuum plumbed to actuate the wastegate on a stock 1Z/AHU that's your problem.

Wastegate is operated by manifold pressure on these.

If you have something other than a stock TC installed you should say so.

Winner winner.. it’s a vacuum operated actuator on an aftermarket turbo

I thought I was clear, sorry.

I swapped the n18 valve in for the n75 because I need vacuum to pull the turbo wastegate open ON A AFTERMARKET TURBO.

did you have the ecm tuned for a vnt and n75 ?

No, this is not a vnt turbo.

Well that's very different.

I may be showing my ignernce here but that's ok if I've got it wrong I learn something.

With a stock AHU when you have too much willy the ECU applies some manifold pressure to open the wastegate.

With your system you want it to apply some vacuum.

Seems to me the basic ECU logic would be the same.

So...Do you have it plumbed right? Common port to the actuator, NO port to the airbox and NC to the vacuum source?

you're probably going to need some custom chips to run that style setup... seems the ahu/1z pressure dependent n75/wastegate setup should only open when the max boost set point is achieved which means it'll be closed until that point is reached, you need it to be open and transmitting vacuum to close the actuator until boost setpoint is achieved, so it's working backward to what you need ...someone please chime in if i'm wrong

It works the same way as the stock turbo except with vacuum

Ls3ase said:

It works the same way as the stock turbo except with vacuum

Click to expand...

If it's a vacuum actuated wastegate then it has to have vacuum applied to close the wastegate and make boost... a pressure actuated wastegate applies pressure to open the wastegate and reduce boost ... from the quick reading I did the vacuum actuated wastegate does not have a spring to keep the wastegate closed but relies purely on vacuum... Is this not the case with your turbo?

Well that's very different too. I assumed vacuum was used to open it.

I'll shut up and listen now.

jimbote said:

If it's a vacuum actuated wastegate then it has to have vacuum applied to close the wastegate and make boost... a pressure actuated wastegate applies pressure to open the wastegate and reduce boost ... from the quick reading I did the vacuum actuated wastegate does not have a spring to keep the wastegate closed but relies purely on vacuum... Is this not the case with your turbo?

Click to expand...

Vacuum opens this wastegated and reduces boost

Someone with a tdi b4 Passat will you...

Post a screen shot of 002 and 006 measuring blocks in vcds?
Post a screen shot of 011 measuring block when supplying the Ecu with 20lbs pressure w/ a mighty vac or something similar

Measure the turbo actuator pressure when supplying the Ecu with 20lbs of pressure w/ a might vac

Measure the voltage at N75 at 1lb and 20lbs pressure to the Ecu


Pretty please?

Ls3ase said:

Someone with a tdi b4 Passat will you...

Post a screen shot of 002 and 006 measuring blocks in vcds?
Post a screen shot of 011 measuring block when supplying the Ecu with 20lbs pressure w/ a mighty vac or something similar

Measure the turbo actuator pressure when supplying the Ecu with 20lbs of pressure w/ a might vac

Measure the voltage at N75 at 1lb and 20lbs pressure to the Ecu


Pretty please?

Click to expand...

I really don't think you understand how your turbo / N75 valve works.

Your wastegate opens when only pressure is applied to it. The N75 valve's job is to block pressure flowing to the wastegate until the ECU turns on the N75 valve. Vacuum has nothing to do with opening your wastegate. There is always manifold pressure going to the N75 valve and when the ECU wants to open the wastegate, it applies a ground to the N75 valves (there is always 12V going to it) allowing that pressure to pass and actually push on the wastegate and opening it. The ECU controls the wastegate with pulse width modulation, not a varying voltage, as it is either "on" or "off". So measuring voltage would give meaningless results as it is always 12V on one side of it and the other side is ground/float state. VCDS will show you the duty cycle of the N75 valve and my experience is that VCDS vs what is the actual duty cycle is the same.

Please tell me what turbo I am running?
Please tell me what happens to MY actuator when vacuum is applied?
Please tell me what happens to my n75 and n18 valves when I use vacuum instead of pressure?
Please tell me you have actually measured 12v at the N75

I've actually tested with vacuum, pressure, and gauges...

David please stop replying to all of my posts anywhere. Your posts are useless.

Ls3ase said:

Please tell me what turbo I am running?
Please tell me what happens to MY actuator when vacuum is applied?
Please tell me what happens to my n75 and n18 valves when I use vacuum instead of pressure?
Please tell me you have actually measured 12v at the N75

I've actually tested with vacuum, pressure, and gauges...

David please stop replying to all of my posts anywhere. Your posts are useless.

Click to expand...

Useless... excuse me, but ***? I don't want to sound arrogant here, but I'm trying to help you, as are the other people here. I have over 20 years experience with TDIs and know the electronics of TDIs inside and out. You can keep on asking questions, but if you don't like the answers that everyone is giving you, you should stop asking them or take their advice as they are correct.

- Please tell me what turbo I am running?
If stock AHU/1Z turbo, then it is a wastegate turbo - it needs pressure to open the wastegate to open it, not vacuum.

- Please tell me what happens to MY actuator when vacuum is applied?
If stock AHU/1Z N75 valve, it doesn't work with vacuum (nor does your turbo).

- Please tell me what happens to my n75 and n18 valves when I use vacuum instead of pressure?
N75 - won't work with vacuum, you need an ALH/BEW N75 for it to work with vacuum.
N18 - will work the way it is supposed to as all N18 valves are vacuum based. N18 valve will NOT work as an N75 valve.

- Please tell me you have actually measured 12v at the N75
N75 have two wires. One goes to pole 87 of the Power Supply Relay and that is *always* battery voltage when the ECU is on. The other wire goes to the ECU, of which the ECU will switch it to ground when it wants to turn on the N75 valve and disconnect it from ground (float) when it wants the N75 valve off. It rapidly pulses the N75 valve many times a second in what is known as a pulse width modulation. This PWM duty cycle is what you see in VCDS represented as a percentage. If you put a voltmeter on it, it will read from 0 to 12V depending on the duty cycle. If you look at it on a scope you will see a nice 12V square wave of varying frequency.

Enjoy my useless post.

He says he has an aftermarket turbo that requires vacuum be applied to open the wastegate (normally closed, requiring vacuum to open).

VeeDubTDI said:

He says he has an aftermarket turbo that requires vacuum be applied to open the wastegate (normally closed, requiring vacuum to open).

Click to expand...

I'll admit that his words are less than concise, but I didn't read replacement or aftermarket turbo and he did say non-VNT, so... is there a turbo out there with a wastegate the requires vacuum to open it? I haven't seen it, but that doesn't mean it doesn't exist. If so, then the other posts in this thread are still correct on these points:

- YOU CAN NOT use an N18 valve (black top, black bottom) to control a turbo.
- YOU CAN NOT use the stock 1Z/AHU N75 valve (black with brass) to control vacuum.
- YOU CAN NOT use the stock 1Z/AHU ECU software to control an ALH style N75 (white top/black bottom).
- N18 and N75 always receive 12V from the J317 relay.
- The ECU provides a PWM ground to the N18 and N75 valve to operate them.

If he has a vacuum controlled turbo, he needs to do the following:
- Get an ALH Style N75 valve (white top / black base).
- Get the 1Z/AHU software changed to run the AFN maps for the N75 valve.

There is no way of getting this combo working with a stock AHU ECU and N75/N18 valve.

Ls3ase said:

Winner winner.. it’s a vacuum operated actuator on an aftermarket turbo

Click to expand...

VeeDubTDI said:

He says he has an aftermarket turbo that requires vacuum be applied to open the wastegate (normally closed, requiring vacuum to open).

Click to expand...

Thank you lol

QuickTD said:

I have never heard of a vacuum operated wastegate. The actuator must be huge or the wastegate very small for this setup to work. I can see such a turbo (or wastegate actuator) being very useful for some other applications, what brand/model turbo or what car is it from?

Click to expand...

I'll post the part number when I get a chance.

The actuator is definitely bigger than the stock turbo.