Piper Arrow IV Turbo Maintenance Manual page 603

D. With engines operating at 2575 RPM and 40.8 to 41.0 in. Hg manifold pressure, mixture control
full rich, reduce RPM and increase throttle until throttle is open. 41.0 in. Hg manifold pressure
should be obtained at approximately 2225 + 25 RPM.
9. Remove test equipment; safety wire the exhaust bypass screw and check nut to the bypass screw
housing; reinstall the cap on the tee of the throttle body housing.
10. The accuracy of the cockpit fuel flow gauge at maximum power can be checked against a calibrated
gauge by connecting the calibrated gauge at the manifold valve and maintaining the gauge on the same level as
the valve while checking pressures and using Chart 7301.
The calibrated gauge fuel line must be purged of air, and the
reference side of the calibrated gauge vented to turbo discharge
pressure.
11. Flight Test: A complete flight test should be made for final adjustments of fuel flow and bypass valve.
The following steps should be followed:
A. At 8,000 feet density altitude, set the engines to operate at 2,450 + 25 RPM and 33.0 to 34.0 in. Hg
manifold pressure.
B. Lean the engine to 25°F rich of peak exhaust gas temperature (EGT).
C. Fuel flow at these conditions should be 12.0 + 0.5 gph.
D. With full rich mixture, full throttle, 2,575 + 0-25 RPM, and 105 MPH airspeed, the manifold
pressure should decrease until the overboost lights go off (40.8 to 41.0 in. Hg), at some point
between 11,500 feet minimum, 12,500 feet maximum density altitude. This point is known as the
"critical altitude." At this point the fuel flow should be 22.0 to 24.0 gph indicated.
E. If a discrepancy in critical altitude was noted, adjust the exhaust bypass valve. (Turning the
exhaust bypass valve screw in one full turn will increase the critical altitude approximately 1,000
feet.) Adjustments of critical altitude in excess of 500 feet may require retrimming of the fuel
flows at 100% power.
F. With full rich mixture, 2,575 RPM, 105 MPH airspeed, and 1,000 to 3,000 feet density altitude,
check the operation of the manifold pressure relief valve. Slowly advance one throttle to the wide
open position. The manifold pressure shall stabilize between 42.0 and 44.0 in. Hg; there shall be
no loss of power, and the fuel flow indication shall be well over the red line. Do not exceed 41.0
in. Hg manifold pressure for more than ten seconds.
Idle speed and idle mixture indication is a function of engine
temperatures. Therefore, at normal ground idle temperatures
(cylinder and oil temperature indications may or may not be "in
the green") idle speed will be approximately 700 RPM, and the
idle mixture check will result in a 25 to 50 RPM increase in
engine speed.
Effectivity
PA-28RT-201T
PIPER AIRCRAFT
PA-28RT-201 / 201T
MAINTENANCE MANUAL
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3C23
73-20-02
Page 73-10
December 1, 1978