Thread: Wastegate Modulator - testing and unpowered behaviour?

Did you test it with ignition on?.... be aware that the modulator is working with pwm command on the earth path to open and gets 12V ignition live to become "active"(which means closed at the beginning), without ignition on it's like a simple open diaphragm.... it's made so to not get overboost if fuse F2 is blown... sorry i didnt read the document before i posted

Originally Posted by sierrafery

Did you test it with ignition on?.... be aware that the modulator is working with pwm command on the earth path to open and gets 12V ignition live to become "active"(which means closed at the beginning), without ignition on it's like a simple open diaphragm.... it's made so to not get overboost if fuse F2 is blown... sorry i didnt read the document before i posted

Hi Fery,

As I understand the WGM is an open from port 1 ( turbo to intercooler pipe connection) to port 3 (waste gate actuator) when it is "de-energised".
So when power is off and when power is supplied but earth path not completed by PWM there is flow 1 -> 3.

When the WGM is "energised" by the PWM providing earth, flow is open from port 2 ( turbo intake trunk) <-> port 3 (waste gate actuator).

In other words if the WGM is activated by a PWM signal it prevents boost pressure reaching the waste gate actuator.
With 0% PWM the waste gate actuator gets full boost pressure.

Anyway I may as well buy a new WGM to check how they work out of the box.

cheers
Paul

Got a new Pierburg WGM from Roverlord this afternoon.

The WGM has been sitting on the desk with 0.5bar vacuum on Port 2 (WGM -> inlet trunk ) for about 30 minutes and the needle didn't budge.
Checking with 0.5, 1.5 and 2.0 bar pressure applied to Port 1 ( turbo outlet -> WGM ) with Port 3 (WGM -> waste gate actuator) capped there is no sign of pressure loss after 20 minutes (at 2.0 bar).

So the Pierburg test procedure appears to be correct for the TD5 WGM.

Posted up some information on how the WGM unit works here:

Wastegate Modulator: Operation | DiscoTD5.com

It's probably a bit long winded but may be of some interest.

It makes sense as if there is a failure the turbo pressure is sent to the wastegate actuator. Safe by design.
I wondered about the third pipe and was curious why they didn't just terminate to atmosphere, but I guess rather than trying to find a place where it won't allow gak back in it makes sense to use the air intake.
As a further benefit I guess it helps to sharpen the system up as you can go from +X psi to -Y psi on the PWM cycle, reducing lag.

This also explains why adjusting the actuator rod gets you boost pressure, if the ECU was controlling boost pressure getting to it then you could set the rod to any old value less than actuation and it shouldn't matter as the ECU would basically be opening and closing the waste gate as it reach desired boost and keeping it on desired boost.

Originally Posted by steve_a

It makes sense as if there is a failure the turbo pressure is sent to the wastegate actuator. Safe by design.
I wondered about the third pipe and was curious why they didn't just terminate to atmosphere, but I guess rather than trying to find a place where it won't allow gak back in it makes sense to use the air intake.
As a further benefit I guess it helps to sharpen the system up as you can go from +X psi to -Y psi on the PWM cycle, reducing lag.

This also explains why adjusting the actuator rod gets you boost pressure, if the ECU was controlling boost pressure getting to it then you could set the rod to any old value less than actuation and it shouldn't matter as the ECU would basically be opening and closing the waste gate as it reach desired boost and keeping it on desired boost.

I think one of the main goals was to reduce wastegate creep and improve mid-range response. As you say it's reducing lag.

The modulator is dissipating around 6W when powered so it wouldn't be practical to have it on by default.
It gets pretty hot if left on for a few minutes.

I suspect the intake is used because the pressure is below atmospheric under boost - you see this in the drop in the AAP reading.
That should make bleeding boost away from the actuator more effective than dumping to air.

Hi, nice work, i have only one comment for a statement of your's(with red) not to contradict you just to say what i found...
it's about that:

Originally Posted by Offtrack

So what does RAVE actually say to support the "activate to limit boost" theory?The following sentence is often pointed to as evidence:
When full boost is reached a control signal is sent to the wastegate modulator, and a vacuum is applied to the wastegate valve.
Interestingly this sentence incorrectly states that vacuum rather than boost operates the waste gate valve. This is often excused as a typo.
But lets examine this from a slightly different perspective.
The turbo intake is subject to suction and we know from the AAP sensor readings that the intake pressure drops below ambient under boost.
We also know from the Pierburg service information that the waste gate actuator is connected to the turbo intake when there the solenoid is energised. Under these conditions the waste gate actuator has a slight vacuum applied.
It's not conclusive either way but there is clearly an error in that statement.

it was quite a while but i stripped a modulator in pieces just to see what's in it and my conclusion is that if the statement in RAVE is not a typo it's a complete error cos when let's say the modulator starts opening the internal valve of it works like a kind'a EGR/ILT valve, it should be no effect of suction from port 2 against port 3 so IMO no "vacuum" can reach that, port 2 can be only an ''exit'' for boost from port 1... "vacuum" from port 2 can eventually affect boost from port 1 which might reduce the boost applied to the wastegate valve when the modulator is in a middle position but if there's no restriction in the intake the drop in AAP is almost inexistent 1-2 KPa which hardly can be named "vacuum" cos the boost which is directed to port 2 is much higher from the beginning when the valve toward port 3 is completely closed if you see what i mean

this theory of mine is 100% supporting your last statement here

Originally Posted by Offtrack

I suspect the intake is used because the pressure is below atmospheric under boost - you see this in the drop in the AAP reading.
That should make bleeding boost away from the actuator more effective than dumping to air.

So IMO your description(except the red part) is spot on and RAVE is 100% wrong(unfortunately not the only case)

Hi Fery,

I'll remove that reference to vacuum because it doesn't really add much to the discussion.

I may be misunderstanding your post, so apologies if that is the case.

The WGM has two paths for airflow.

I've enhanced the flow annotations in the pierburg information to make this a bit clearer.

First is with the solenoid de-energised, where pressure can flow between port 1 and port 3 in both directions.
That corresponds with the connections from turbo-intercooler pipe to the WGM and from the WGM to wastegate actuator.

WGMdeenergised.png

Second is when the solenoid is energised by the PWM signal completing the earth path.
In this case pressure flows from the wastegate actuator (Port 3) to the air intake trunk (Port 2).

WGM energised.png

In both cases port 3 is open, and the solenoid switches between port 1 and port 2 .

cheers
Paul