03-I 9
Auxiliary Systems
03-l 9
FUEL SYSTEM DIAGNOSING AND TESTING
NOTE: For the following
tests,TEMPORARILY
place a
jumper wire across the terminals of the oil pressure
switch.
Electrical
1. Connect the positive lead of a voltmeter to the
pump power wire, and the negative lead to the
pump housing.
2. Turn on the ignition switch.
3. The voltmeter should read 12 volts. If not, check
the power supply to the pump, and the ground
wire between pump housing and engine cylinder
block.
4. ONCE YOU HAVE ESTABLISHED THE
INTEGRITY OF THE POWER SUPPLY AND
GROUND to the pump, if it still will not operate,
replace the pump assembly.
Fuel Supply and Pressure
If a problem with fuel supply or delivery is suspected,
first ensure that there is fuel in the tank. Next ensure
that the 70 micron filter inside the pump housing is
clean. Once these items have been checked and
verified, proceed as follows:
1.
Tee a pressure gauge into the fuel line at the
carburetor inlet.
2. Turn on the ignition switch, but do not start the
engine.
3.
The pump should “click” rapidly for a short time,
and pressure should build to, and level off at, 6.0
to 7.5 PSI.
SERVICE CHECK CHART
4.
If pressure fails to come up, check for an
obstruction in the supply line from the tank to the
pump, and between the pump and carburetor.
5.
Ensure that the fuel cap vent is operating
properly. The vent should allow air to enter the
tank as fuel is removed. Correct any obstruction
or restriction found.
IF NO OBSTRUCTION IS FOUND, AND THE
ELECTRICAL SUPPLY, GROUND, AND FUEL
SUPPLY TO THE PUMP AS DESCRIBED ABOVE,
ARE VERIFIED ALL RIGHT, REPLACE THE PUMP
ASSEMBLY.
6. Start the engine and allow it to come up to
operating temperature.
7. Set the throttle control to high idle. Place as full
a load onto the engine as possible.
8. Fuel pressure should be maintained at a
minimum of 4 PSI.
9. If fuel pressure cannot be maintained, verify that
all of the above checks have been carried out.
IF ALL OF THE ABOVE CHECKS HAVE BEEN
CARRIED OUT, AND FUEL PRESSURE CANNOT BE
MAINTAINED, REPLACE THE FUEL PUMP
ASSEMBLY.
WARNING: ONCE ALL OF THE ABOVETESTS
ARE COMPLETED, REMOVE THE JUMPER WIRE
FROM THE OIL PRESSURE SWITCH.
For additional diagnostic information, see the Service
Check Chart below.
CONDITION
lnsuff icient fuel delivery
Pump not operating
Carburetor flooding
1 Fuel pump leaks
POSSIBLE SOURCE
l
Clogged pump filter, screen, or fuel filter.
l
A break or restriction in fuel lines.
l
An incorrect float level, malfunctioning inlet
needle valve, or clogged inlet screen in the
carburetor.
l
Damaged, loose ground, or improper
wiring.
l
Worn needle and seat assembly in
l
Replace worn needle and seat assembly
carburetor.
in carburetor.
l
Wrong pump application: that is, standard
pressure pump for low pressure
application.
l
Air leak on inlet side of pump due to holes
in fuel line or loose fittings.
l
Fuel line fitting connections at pump are
loose or dirty.
ACTION
I
l
Clean or replace filter.
l
Repair fuel line or remove restriction.
l
Repair or replace as needed.
l
Inspect all mounting or wiring.
l
Change to a low pressure pump
l
Replace fuel line, and tighten fittings (apply
a sealer, if necessary).
pump-
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