Just bought a 2005 WRX with the stock turbo gauge. Is it normal for
the needle to go all over the place when driving?
The gauge acts like it has a mind of its own. At idle the gauge is
steady, at less than zero, and when the car is off it is at zero, but
while driving it is all over the place! Thanks for any info.
It sounds like your gauge is normal, you just have to learn how to
read it.
At idle, light throttle/crusing, and decelerating, the gauge will show
vacuum. The vacuum at idle will normally be steady but may change
slightly if the AC is running (you'll see it move as the compressor
cycles and changes the engine load), you turn the wheel when stopped
or parking (power steering pump also loads the engine), a heavy
electrical load kicks in (fans, etc.). When decelerating in gear with
your foot completely off the gas you'll see more vacuum than at idle,
this is normal.
As you accelerate and place a heavier load on the engine, you'll see
the gauge move out of vacuum, past zero (which represents atmospheric
pressure) and into positive pressure or boost. The amount of boost you
see depends on a few things, including what gear you're in, RPM,
engine load and throttle position. The factory boost control system
won't give you full boost until you get pretty far into the throttle,
up to that point you'll get wastegate pressure or about half of full
boost.
The gauge is calibrated in Mpa, which is a metric scale for pressure.
..05 on the gauge corresponds to about 7 PSI, .1 about 14 PSI.
Coincidentally on the WRX 7 PSI is wastegate pressure, and 14 PSI is
approximately maximum boost.
