Dead Turbo Boost Gage
 
Copyright 2000 Frank Zemaitis/STE, ltd. All Rights Reserved

Dead Boost Gage.  Or the "torque meter" as Nissan calls it.  This sensor does not actually measure boost.  Rather it measures negative manifold pressure, or vacuum. The tach display is a 2 dimensional display.  RPM is expressed horizontally and boost (torque) is expressed vertically. Loosely, this is relative to the amount of torque the engine is developing.  It's display function is inversely related to the vacuum level.  In other words, at idle, the manifold vacuum is at it's greatest, and the vertical bars are at the lowest.  At high RPM, vacuum is at it's lowest (the manifold actually may be pressurized by the turbo) and the vertical bars are at their highest.  When the vacuum hose breaks, the sensor sees no pressure change and the bars stay up.

This is one of the easiest fixes.  If the vertical bars of the torque/RPM gage are fully lit there is a break in the vacuum hose that runs from the right side if the manifold to the boost sensor.  The hose is attached to a fitting on the right side of the manifold at the mid point.  This hose runs around the back of the engine and up to the boost sensor located in the left front corner of the engine compartment under the spark coil.  The hose connection is under the sensor where it can't be seen. You can squeeze your fingers down there and feel it.  This is where the hose commonly breaks.  Best thing to do is to replace the entire hose rather that just cutting it back.

TERUG NAAR TECHNIEK