Rockwell Commander 112 - FUEL INJECTION SYSTEM

SECTION IV
POWER PLANT
AND PROPELLER
MAINTENANCE MANUAL
ROCKWELL
COMMANDER
112/B/TC /TCA
tion II for cleaning and installation.
MODELS 112TC/TCA. The induction air system
utilizes a flock-coated induction air filter. The filter
element is installed in the filter housing located on
the
lower right side of the cowling near the firewall.
Refer to Section II for cleaning and installation.
FUEL INJECTION SYSTEM
MODELS 112/B. Filtered air is introduced into the
engine through the servo regulator body, then flows
into an
air intake riser where it is distributed to each
cylinder by individual intake pipes. The amount of air
entering the engine is controlled by a throttle valve
(butterfly) contained in the body of the fuel injection
servo regulator. Fuel is metered and distributed to
the individual cylinders by the servo regulator and
fuel flow
divider valve. The fuel-air ratio is deter-
mined by the pOSition of the throttle valve and air
senSing functions of the servo regulator. Fuel and
air are mixed within the cylinder. The fuel injection
system consists of the air flow senSing and fuel con-
trol subsystems. Components of the injection system
are: the servo valve, fuel control unit, fuel flow
divider valve, and air bleed nozzles. The servo valve
and fuel
control unit are contained within the throttle
body casting, installed on the engine intake manifold
air inlet.
SERVO REGULATOR
MODELS 112/B. The servo regulator is the basic
component of the fuel injection system. Induction air
enters the throttle body, passes through the venturi
and by the throttle valve and into the engine. As
the air passes through the throttle body, air pres-
sure is sensed by impact tubes which lead to one side
of the servo regulator air diaphragm. The other Side
of this diaphragm is exposed to low pressure which
is sensed at the venturi throat of the throttle body
(see
Figure 4-5). A ball servo valve and a fuel/air
diaphragm operates on the pressure differential be-
tween unmetered and metered fuel pressure. The
air metering force applied to the air diaphragm of
the servo regulator is directly proportional to the
velocity
of air flOwing through the venturi to the
engine.
Air velocity is controlled by the position of
the
throttle valve; therefore, a change in throttle
setting will alter the position of the fuel/air diaphragm.
This causes the position of the ball servo valve to vary.
The pressure differential across the ball servo valve
opposes the
action of the air diaphragm and tends to
open or close the ball servo valve. This provides
regulated servo pressure for operation of the fuel
flow
divider valve which schedules a fuel flow that is
correctly proportioned to the engine inlet airflow. A
balanced fuel flow condition will exist when servo
pressure on the fuel flow divider valve and ball servo
valve is equal to the air metering force at the air di-
4-8
aphragm of the servo regulator. The richer fuel
mixture required during engine idle is obtained by
using a constant head spring on the lower side of the
air sensing diaphragm. Fuel pump pressure, which
is recorded on the engine gage unit, is taken from a
port on the forward side of the servo regulator fuel
control unit. Fuel flow readings are obtained from
the metered fuel side of the fuel flow divider valve.
MODELS 112/B. CLEANING AND INSPECTION. The
following procedures apply to cleaning and inspection
of the servo regulator. Remove and clean the fuel
inlet screen at the first 25 hours and each 50 hours
of operation thereafter.
a. Remove upper cowling.
b. Inspect servo regulator and all fuel lines for
tightness and evidence of fuel leakage.
NOI.
Slight fuel stains adj acent to the air
bleed nozzles are normal.
c. Clean screen assembly in cleaning solvent and
dry with filtered compressed air.
d. Inspect screen assembly to determine service-
ability. Replace screen assembly if deformed or
deteriorated.
e. Place new O-ring on screen assembly and install
screen assembly in servo regulator. Tighten screen
retainer to 35-40 inch-pounds.
f. Check
servo regulator for security of attach-
ment.
g. Check throttle, mixture, and alternate air con-
trol rods, rod ends and levers for security and con-
dition of
rod ends.
h. Lubricate ends of throttle shaft with instrument
oil.
i. Lightly lubricate rod ends of throttle, mixture,
and alternate air control rods.
j. Check mixture and throttle controls for freedom
of operation.
MODELS 112/B. ADJUSTMENT. Adjustments to the
servo regulator are confined to idle speed and mixture.
If there is an appreciable amount of wind, locate air-
craft in crosswind position before making idle speed
and mixture adjustment., This will prevent false load-
ing of the engine caused by the affect of wind velocity
on the propeller.
a. Start and warm engine until oil and cylinder head
temperatures are in normal operating range.
b. Check magneto drop, see Section II. If drop is
normal, proceed with idle adjustment.
c. Set throttle stop-screw so engine idles at 550-
650 RPM. If the RPM varies significantly after making
mixture adjustment during following steps, readjust
to desired RPM.
d. When idling-speed has stabilized, move mixture
control lever toward IDLE CUTOFF position and ob-
Copyright Commander Owners Group 2013 All Rights Reserved
**unofficial copy**