Wastegate operation clarification please

[Mudbug63]

Ok I am finding conflicting information can someone confirm if this is correct?


1. The wastegate is held closed by a spring.
2. To limit boost the vacuum is applied helping override the spring and allowing the exhaust to bypass the turbine blades.

The vacuum is the main source of control but the spring is a fail safe, correct?


If my understanding is correct and I have low boost could a weak spring be the issue? 10PSI is the max I have ever seen with the vacuum line hooked up and can get 17-18 with the vacuum disconnected.

I could see a weak spring allowing the vacuum motor to over compensate.

Is this possible or am I off in left field?

[stroker/stonemaison]

heres a bump for ya

[superduty4x4]

The red line going to the wastegate is a pressure line, not vacuum. As boost rises, some of it passes through the red line and helps compress the spring inside the canister.
If you can only get 10 psi boost something is wrong... are you sure you don't have a boost leak some place? The wastegate is adjustable, you can remove the canister from the turbo and shorten the actuator arm by turning the end of it. This will put more pressure on the spring, holding the WG closed for longer. You might give that a try and see if it helps you any.

[Mudbug63]

Originally Posted by superduty4x4

The red line going to the wastegate is a pressure line, not vacuum. As boost rises, some of it passes through the red line and helps compress the spring inside the canister.
If you can only get 10 psi boost something is wrong... are you sure you don't have a boost leak some place? The wastegate is adjustable, you can remove the canister from the turbo and shorten the actuator arm by turning the end of it. This will put more pressure on the spring, holding the WG closed for longer. You might give that a try and see if it helps you any.

I guess I need to look at the line routing again. I would have sworn the one line attaches to the intake between the air filter and the turbo inlet. That would be a vacuum, Then through the control unit/valve. ( cant recall the correct name ) and on to the waste gate. Maybe I am missing a line I only have 2

[superduty4x4]

There should be a green line in the intake between the turbo and the air filter... this where excess boost is dumped when the wastegate opens. The red line that hooks to the wastegate actuator is a pressure line IIRC. Maybe I'm wrong... it has happened once or twice before And there's no vacuum in the intake on a PSD, that's why we have to have a vac pump for the ESOF and A/C operation.

[dieselcrawler]

Originally Posted by superduty4x4

And there's no vacuum in the intake on a PSD.

The intake is under pressure, that is the whole reason for the turbo, it's compressing the air going into the intake. That's why your boost gauge line is hooked into the intake, and reads pressure, not vacuum. Diesels only show boost, however on a turbo'd gasser, you'll have both vacuum or boost, depending on the contitions.

[superduty4x4]

Good points Greg!

[Mudbug63]

Understood that the once the air leaves the Turbo it is under boost.

My thinking was that the slight vacuum created by the air cleaner restriction in the intake tube between the filter and the turbo when the turbo was spooled was somehow being used to manipulate the wastegate. Obviously wrong.

I fully understand that a PSD does not create vacuum like a gasser.

The fact that it is flowing in reverse of what I thought and is dumping into the intake makes perfect sense. I just did not see the pressure tap at the turbo to feed the system. Is the feed internal the mounting of the wastegate actuator or did I miss a tube?

That all being said let me see if I understand the process now.

1. The wastegate is held shut by a spring.
2. As boost builds part of it is tapped to power the actuator.
3. The control assemble that the red and green hoses connect to control the amount of pressure applied to the actuator in order to control boost.

Close?

[Robsr]

Right on! another factor is fuel. Fuel rate is also used to limit boost via the MAP sensor.

[superduty4x4]

Originally Posted by Mudbug63

Understood that the once the air leaves the Turbo it is under boost.

My thinking was that the slight vacuum created by the air cleaner restriction in the intake tube between the filter and the turbo when the turbo was spooled was somehow being used to manipulate the wastegate. Obviously wrong.

I fully understand that a PSD does not create vacuum like a gasser.

The fact that it is flowing in reverse of what I thought and is dumping into the intake makes perfect sense. I just did not see the pressure tap at the turbo to feed the system. Is the feed internal the mounting of the wastegate actuator or did I miss a tube?

That all being said let me see if I understand the process now.

1. The wastegate is held shut by a spring.
2. As boost builds part of it is tapped to power the actuator.
3. The control assemble that the red and green hoses connect to control the amount of pressure applied to the actuator in order to control boost.

Close?

You got it. There should be a red line hooked to the wastegate actuator (gold canister bolted on top of the turbo) on the driver's side of it. If not, the red hose is probably hooked to a stud on one of your IC boot clamps because someone has unplugged it.