I have a Legacy with an IO-550 engine.  I installed the fuel pressure sensor to measure metered pressure for three reasons:

 

1.  That's what the Chelton installation manual suggested.

2.  That's what seemed to me to be the most diagnostic fuel pressure, since that's what the fuel injectors are seeing.

3.  The SID97-3 fuel setup procedure uses metered fuel pressure at full power and unmetered fuel pressure at idle.  I think the full power pressure is more valuable than the unmetered idle fuel pressure. 

 

Every fuel pressure spec I've seen in the TCM engine manuals, as well as SID97-3, includes metered and unmetered pressures.  However, to fully comply with SID97-3 fuel system setup requires pressure gauges on both the unmetered and metered pressures.  It says to set the unmetered fuel pressure at idle and the metered fuel pressure at full power.  It's in a footnote, which says:

 

    FULL POWER unmetered fuel pump pressure limits are provided for reference only.
    Use metered fuel pressure specifications for adjustments at full power.

 

By the way, my metered fuel pressure at idle 1,000 RPM is 4 PSI.

 

Dennis

Legacy