Piper PA-34-200T Seneca II Service Manual Download

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PIPER SENECA II SERVICE MANUAL

IX - FUEL SYSTEM

01/01/09

2D6

CAUTION: EXCESSIVE FUEL PRESSURE AND VERY RICH FUEL/AIR MIXTURES WILL

OCCUR IF THE HI POSITION IS ENERGIZED WHEN THE ENGINE FUEL
INJECTION SYSTEM IS FUNCTIONING NORMALLY.

In case of a failed engine driven fuel pump, auxiliary fuel pressure may be selected. Adequate pressure
and fuel flow will be supplied for up to approximately 75% power. Manual leaning to correct fuel flow
will be required at altitudes above 15,000 feet and for RPM’s less than 2300. An absolute pressure
switch automatically selects a lower fuel pressure when the throttle is reduced below 21 in. Hg manifold
pressure and the HI auxiliary fuel pump is on.

Low auxiliary fuel pressure is available and may be used during normal engine operation both on the
ground and in flight for vapor suppression should it be necessary as evidenced by unstable engine
operation during idle or at high altitudes.

There are two separate spring loaded OFF primer button type switches, located adjacent to the starter
switches. These switches are used to select the HI auxiliary fuel pump operation for priming, irrespective
of other switch positions. These primer buttons may be used for both hot or cold engine starts.

On airplanes equipped with an optional engine primer system, Piper Service Kit No. 761-094v, the
primer switch location and actuation is the same as the basic airplane. However, this system includes
several parts not found in the basic airplane but which make up an integral part of the engine fuel
system. The components of the system are an electrically operated diverter valve, located on the engine
in the metered fuel supply line between the air throttle valve and the manifold valve, two primer nozzles,
located in the intake manifold on each side of the engine, the interconnecting fuel lines, and fine wire
spark plugs. Actuation of the engine primer switch operates the auxiliary electric fuel pump on HI and
energizes the diverter valve which supplies fuel to each primer nozzle in the intake manifold. The
diverter valve does not shut off all fuel flow to the manifold valve, therefore some quantity of fuel is also
supplied to each cylinder nozzle during priming. Operation of the auxiliary fuel pump on HI and LO is
unchanged.

9-3. TROUBLESHOOTING.

Table IX-II, located in the back of this section, lists troubles which may occur in the mechanical or
electrical portions of the fuel system, the probable cause and a suggested remedy. When troubleshooting,
first check from the fuel supply or power source to the item affected. If the suggested remedy does not
eliminate the problem, the trouble probably exists inside the component involved. It will then be
necessary to remove the defective component for repair or replace it with an identical serviceable unit.

Piper PA-34-200T Seneca II, Service Manual

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