Most important guages for boosted engines?

[cali yaris]

battleversion -- great links!

Just because it's 0-5v does not mean it's a wideband sensor like the kind that come with gauges. The Yaris sensor is a proprietary, unusual hybrid design. To demonstrate this, you cannot replace it with a 0-5v wideband A/F sensor and have it work. (see bold print below)

The rear sensor is an "normal" O2 sensor.

A WRAF sensor is essentially a smarter oxygen sensor with some additional internal circuitry that allows it to precisely determine the exact air/fuel ratio of the engine. Like an ordinary oxygen sensor, it reacts to changing oxygen levels in the exhaust. But unlike an ordinary oxygen sensor, the output signal from a WRAF sensor does not change abruptly when the air/fuel mixture goes rich or lean.