
RENR9968-02 27
Testing and Adjusting Section
Testing and Adjusting
Section
Fuel System
i02486828
Fuel System - Inspect
SMCS Code: 1250-040
A problem with the components that send fuel to
the engine can cause low fuel pressure. T his can
decrease engine performance.
1. Check the fuel level in the fuel tank. Ensure that
the vent in the fuel cap is not fi lle d with dirt.
2. Check all fuel lines for fuel leakage. The fuel lines
must be free from restrictions and faulty bends.
Verify that the fuel return line is not collapsed.
3. Install a new fuel fi lter.
4. Cut the old filter open with the 175 -75 46 Oil
Filter Cutter Gp. Inspect the filter for exce ss
contamination. Determine the source of the
contamination. Make the necessary repairs.
5. Service the primary fuel filter (if equipped).
6. Operate the hand priming pump (if equipped).
If excessive resistance is felt, inspect the fuel
pressure regulating valve. If uneven resistance is
felt, test for air in the fuel. Refer to Testing and
Adjusting, “Air in Fuel - Test” for more information.
7. Remove any air tha t may be in the fuel system.
Refer to Testing and Adjusting, “Fuel System -
Prime”.
i02486845
Air in Fuel - Test
SMCS Code: 1280-081
This procedure checks for air in the fuel. This
procedure also assists in finding the source of the air.
1. Examine the fuel system for leaks. Ensure that
the f uel line fittings are properly tightened. Check
the fuel level in the fuel tank. Air can enter the
fuelsystemonthesuctionsidebetweenthefuel
transfer pump and the fuel tank.
2. Install a 2P-8278 Tube As (SIGHT GA UGE) in
the fuel return line. When possible, install the sight
gauge in a s traight section of the fuel line that is
at least 304.8 mm (12 inches) long. Do not install
the sight gauge near the following devices that
create turbulence:
•
Elbows
•
Relief valves
•
Check valves
Observe the fuel flow during engine cran king.
Look for air bubbles in the fuel. If there is no fuel
in the sight gauge, prime the fuel system. Refer
to Testin g and Adjusting, “Fuel Sy ste m - Prime ”
for more information. If the engine starts, check
for air in the fuel at varying en gine speeds. When
possible, operate the engine under the conditions
which have been suspect of air in the fuel.
g010966
78
Illustration 21
2P-8278 Tube As (SIGHT GAUGE)
(1) A ste
ady stream of small bubbles with a diameter of
approxi
mately 1.60 mm (0.063 inch) is an acceptable amount
of air in
the fuel.
(2) Bubb
les with a diameter of approximately 6.35 mm ( 0.250 inch)
are also
acceptable if there is two seconds to three seconds
interva
ls between bubbles.
(3) Exce
ssive air bub bles in the fuel are not acceptable.
3. If excessive air is seen in the sight gauge in the
fuel ret
urn line, install a second sight gauge at
the inlet to the fuel transfer pump. If a second
sight gauge is not available, move the sight gauge
from the
fuel return line and install the sight gauge
at the inlet to the fuel transfer pump. Observe
the fuel flow during engine cranking. Look for air
bubble
s in the fuel. If the engine starts, check for
air in the fuel at varying engine speeds.