I learned something about waste-gate cans today

[DaveP]

They go bad and won't hold pressure. I've never thought of checking one before. But I don't trust anything on DesertSy as everything on this 175K Sy is really old and jankey. And "checking costs nothing". So I whipped out the radiator pressure checker, plugged the hose onto the waste-gate can, and pumped 'er up. It moved, but wouldn't hold. I had an extra in my stash. It held just fine.

Now for a question? How can you bench-check waste-gate rod adjustment, besides the "1/2 a hole overlap" on the length? When I pressurized it, it started to move at about 2-3-psi. They both did, even the bad one. I thought it's supposed to be 7-8psi. What am I missing?

 

[Quickstop [UK]]

Re: I learned something about waste-gate cans today

Just thinking it through but the valve does not have to overcome the spring pressure up until 8 psi.

Above 8 psi and the pressure from the solenoid is forcing the valve closed, below 8psi and all the work is being done by the spring. Any slack in the system wil be taken up once the spring and valve are in contact no?

Also, the gate isn't binary - it is analogue so a small amount of pressure will cause a small deflection. The spring in it means that you need the full force of 8psi to open the gate all the way.

It's the basic law of springs; f = 1/2 k x x (x squared) (spring equation)

 

[DaveP]

Re: I learned something about waste-gate cans today

It's overcoming the spring pressure at 2-3psi. Pressure opens it against the spring.

Is it that I don't have the rod tight enough? The tighter it is, the higher the pressure required to overcome the spring, because the spring is "pre-loaded". I'll go out and mess with it.

 

[DaveP]

Re: I learned something about waste-gate cans today

Above 8 psi and the pressure from the solenoid is forcing the valve closed, below 8psi and all the work is being done by the spring.

I may not understand why it moves at 2 psi, but I know how the waste-gate system works, and it's not like you describe. Below 8psi, the wastegate is receiving full signal from the compressor. Above 8psi the ECM PWM's the solenoid to interrupt some of the signal;, thus raising the boost above base (non-pwm'd) 8psi.

Also, the gate isn't binary - it is analogue so a small amount of pressure will cause a small deflection. The spring in it means that you need the full force of 8psi to open the gate all the way.

I'm thinking that the gate is like a thermostat. It begins to open at the set-point. Not "full open" at the set-point.

 

[warmpancakes]

Re: I learned something about waste-gate cans today

son of a bitch Thanks Dave ive been holding off on buying a pressure tester I just grabbed a new vac tester but since I have 2 rad pressure testers Thanks dave

 

[Quickstop [UK]]

Re: I learned something about waste-gate cans today

I may not understand why it moves at 2 psi, but I know how the waste-gate system works, and it's not like you describe. Below 8psi, the wastegate is receiving full signal from the compressor. Above 8psi the ECM PWM's the solenoid to interrupt some of the signal;, thus raising the boost above base (non-pwm'd) 8psi.

I'm thinking that the gate is like a thermostat. It begins to open at the set-point. Not "full open" at the set-point.

I don't have a stock setup and I always get confused with these systems...

I thought that the default value with no solenoid is 8-9 psi based on the spring and that above that, the boost would force the spring open. Anything above 9 psi would mean that there is an additional signal rather than less... So the solenoid is providing extra line pressure from the compressor to keep boost valve closed no?

I must be reasoning it wrong...

 

[dgoodhue]

Re: I learned something about waste-gate cans today

When I pressurized it, it started to move at about 2-3-psi. They both did, even the bad one. I thought it's supposed to be 7-8psi. What am I missing?

It doesn't surprise me it moved before 8-9psi. I hooked mine upto a mitivac and it seemed to move at two pumps a slight bit (gauge only read vacuum). I would have guessed it moved at 4-5 psi though.

As for how it works. I will try to explain this in short post without spending a bunch of time. Think of two systems separately, the actuator and wastgate flap.

The wategate actuator starts to move at 3 psi. (throwing random numbers out) At 6 psi the rod moves 6mm, 9 psi - 12mm, 12psi - 18mm. [I suspect the number will be somewhat linear once the rods starts to move.]

The wastegate flap enable the turbo to make full boost when closed. With it open 5 mm might make 14psi, 10mm -9psi 15mm 4psi. again guessing at numbers.

If we consider the 3/4 pin overlap as well it shortens rod movement of the actuator before it moves. Let's use 2mm in the example above.

The equilibrium of the rod length and wastegate flap is where the base boost will be. Inthe example above its 9psi when the flap opens 10mm and the actuator opens 12mm minus the 2mm pin overlap.

 

[It's just a six]

Re: I learned something about waste-gate cans today

That is what is called boost creep.
The wasegate valve will actually open before you see your set boost pressure causing the turbo to spool up slower.

 

[midnightbluS10]

Re: I learned something about waste-gate cans today

That is what is called boost creep.
The wasegate valve will actually open before you see your set boost pressure causing the turbo to spool up slower.

Since when? I always thought boost creep was when boost can't be controlled completely and rises above a set point controlled by the wastegate. For example you have it set for 15 psi and it gradually rises higher.

 

[denny]

Re: I learned something about waste-gate cans today

That is what is called boost creep.
The wasegate valve will actually open before you see your set boost pressure causing the turbo to spool up slower.

Boost creep is when it over boost slowly, usually an undersize wastegate or open exhaust.

correct, without a boost controller the wastegate valve will open before your set boost.

 

[DaveP]

Re: I learned something about waste-gate cans today

Now for a question? How can you bench-check waste-gate rod adjustment, besides the "1/2 a hole overlap" on the length?

I can now answer my own question. I was looking for something else last night in the Service Supplement, and ran across "Wastegate Actuator Adjustment". I had never seen this before.

The spec is .020-.060 of travel at 4.5-5.0 psi of air pressure. If the travel is greater, then shorten the rod. This increases the spring pre-load, which raises base boost.

EDIT: I remembered I have a 0-30psi calibration gauge. Very accurate. Much more so than the gauge in the radiator pressure checker. I didn't set up the dial indicator, but I pumped it up to 4.5 psi. The rod moved just a tad. By hand, I could push it back to the closed position. It looked to be about 40-50 thou by eyeball. Well within spec.

So yes Virginia, there is a way to check and set the waste-gate on the bench. But you need a pressure pump, an accurate pressure gauge, and a dial indicator, or trained eye-ball.

 

[Throws]

Re: I learned something about waste-gate cans today

They go bad and won't hold pressure. I've never thought of checking one before. But I don't trust anything on DesertSy as everything on this 175K Sy is really old and jankey. And "checking costs nothing". So I whipped out the radiator pressure checker, plugged the hose onto the waste-gate can, and pumped 'er up. It moved, but wouldn't hold. I had an extra in my stash. It held just fine.

What symptoms were you seeing that prompted you to check?

-P

 

[DaveP]

Re: I learned something about waste-gate cans today

. But I don't trust anything on DesertSy as everything on this 175K Sy is really old and jankey. And "checking costs nothing".

What symptoms were you seeing that prompted you to check?

I'm rebuilding the entire Syclone. Engine, Transmission, T-case, wiring, interior refurbishing, etc. I don't trust anything on this truck, and because it wasn't drivable when I purchased it, I know nothing about it. But I'm learning. Pretty much everything is f ucked up. . And because of the thoroughness with which I approach my projects, I check stuff, if I can figure out a test procedure with material and/or tools that I have on hand. Like I did for the waste-gate.

Checking Costs Nothing

 

[DaveP]

Re: I learned something about waste-gate cans today

. But I don't trust anything on DesertSy as everything on this 175K Sy is really old and jankey. And "checking costs nothing".

What symptoms were you seeing that prompted you to check?

I'm rebuilding the entire Syclone. Engine, Transmission, T-case, wiring, interior refurbishing, etc. I don't trust anything on this truck, and because it wasn't drivable when I purchased it, I know nothing about it. But I'm learning. Pretty much everything is f'd up. . And because of the thoroughness with which I approach my projects, I check stuff, if I can figure out a test procedure with material and/or tools that I have on hand. Like I did for the waste-gate.

Checking Costs Nothing