wastegate hoses--type 44

[Wallace White]

Ameer -

I think I've got all this straight: the bottom chamber is always
connected to intake manifold pressure. The upper chamber is normally
connected to vacuum, as you mention. At about 1.2 bar, the intake
pressure in the bottom chamber is sufficient to overcome the spring in
the upper chamber.

When the ECU turns on the wastegate frequency valve, the upper chamber
is connected to intake manifold pressure--just like the bottom chamber.
At steady state, then, the upper chamber always "wins," but it's never
at steady state. The WGFV is cycled at maybe 4 Hz, with varying duty
cycle, by the ECU towards a target manifold pressure, 1.4 bar.

Scott Mockry's sight gives nice instructions on hooking up a test LED to
the WGFV and watching its operation. I did this a while ago and had
great fun watching it as I drove. I think the ECU never opens the WGFV
at 100% duty cycle; it keeps toggling even when the manifold pressure is
low. 

- Wallace
  '87 5kcstq 168k