losing power code 78 vac seems ok

[brokenparts1]

Hey everyone,
My truck islosing power, and its throwing code 78, but I've got good vac going to my waste gate valve. could the valve ( the plunger deal on the side of the turbo) be bad? The waste gate salenoid is relativily new. It seems like its getting more rattly at idle lately too. Any thaughts
Thanks ryan

[w_huisman]

What make and model truck are you having troubles with?

Vacuum system failure points are:
1) pump
2) solenoid
3) lines
4) wastegate diaphragm/actuator

Sounds as though 2) is not likely the culprit. You will need a vacuum gauge to rule out 1) if it isn't obviously failing by making the usual machine gun racket.

Visually inspect the lines for cracks or breaks to rule out 3).

After that, all that's left is the actuator. Someone else may have a way to test one, but I don't have any experience doing so.

[3bals]

The waste gate controller on the side of the turbo should be easy to see if it's working or not by unplugging the vac line to it while the engine is running. If it moves one way or another when you unplug it, then aleast the actuator is working.

Jody

[brokenparts1]

Thanks guys. sorry I didn't explain things better. It's a 1995 gmc 6.5, I already checked the vac pump with a gauge, it pulls 25, The salenoid pulls 15 at the actuator, I unplugged the line at the actuator to check it, the rod moves freely with the engine off and pretty easily even while running. So I guess my question should have been where do I get a actuatot valve? Is the dealer the only option? Walt said he might have a good used one for 125.
Thanks again ryan