Piper Cherokee LANCE, Service Manual

Page: 464 / 854

PIPER CHEROKEE SIX / LANCE SERVICE MANUAL
VIII - FUEL SYSTEM 03/27/08
2J4
8-14a. FUEL QUANTITY SENDING UNIT (P/N 548-671) CALIBRATION.
NOTE: The fuel quantity sending unit, Piper part number 548-671 (Rochester Gauges P/N 7740-309) is
NOT compatible with any A.C. Sparkplug or Stewart Warner fuel quantity gauge. The
Rochester fuel quantity sending unit MUST be used only with Rochester fuel quantity gauges.
Refer to Service Spares Letter Number 406 for appropriate fuel quantity gauge/sender systems.
Instructions:
a. Perform sending unit/gauge system check per section 8 of the aircraft service manual.
b. Make appropriate log book entry.
NOTE: If an adjustment of the fuel quantity sending unit, Piper P/N 548-671, is required, refer to
instructions below.
1. Fasten unit to a fabricated checking fixture with washers and nuts (Refer to Figure 8-3a for
dimensions of fuel quantity sending unit checking fixture).
2. Ascertain that with the float just touching the top of a 0.27 inch spacer block, the resistance of
the sending unit is 3 ± .5 ohms. Should the resistance of the sending unit not fall into this
range, adjust the arm of the float assembly by gently bending it as indicated in Figure 8-3b.
The entire float must be horizontal to the base of the fixture.
3. Remove the sending unit from the checking fixture and connect it to an ohmmeter. Allow the
float arm to rest on the bottom mechanical stop. A resistance of 0 ± .5 ohms should be
indicated at this position. Move the float assembly to the upper mechanical stop. A resistance
of 45 ± 2 ohms should be indicated at this position.
4. Check for dead spots by slowly moving the float arm from the bottom stop to the upper stop
and back. Watch the ohmmeter indicator, it should steadily move up and down the scale with
out fluctuation as the float arm is moved.
5. If an incorrect resistance and/or dead spots are found, the sending unit should be replaced.