Guardian 4389 Repair Manual page 106

SECTION 4.4
DIAGNOSTIC TESTS
TEST 51 - CHECK FUEL SUPPLY AND
PRESSURE
DISCUSSION:
The air-cooled prepackaged generator was factory
tested and adjusted using natural gas as a fuel. If
desired, LP (propane) gas may be used. However,
when changing over to propane, some minor adjust-
ments are required. The following facts apply:
• An adequate gas supply and sufficient fuel pressure
must be available or the engine will not start.
• Minimum recommended gaseous fuel pressure at
the generator fuel inlet connection is 11 inches
water column (6.38 ounces per square inch).
• Maximum gaseous fuel pressure at the generator
fuel inlet connection is 14 inches water column (8
ounces per square inch).
• When propane gas is used, only a "vapor withdraw-
al" system may be used. This type of system utilizes
the gas that form above the liquid fuel the vapor
pressure must be high enough engine operation.
• The gaseous fuel system must be properly tested
for leaks following installation and periodically
thereafter. No leakage is permitted. Leak test meth-
ods must comply strictly with gas codes.
DANGER: GASEOUS FUELS ARE HIGHLY
!
EXPLOSIVE. DO NOT USE FLAME OR HEAT
TO TEST THE FUEL SYSTEM FOR LEAKS.
NATURAL GAS IS LIGHTER THAN AIR,
TENDS TO SETTLE IN HIGH PLACES. LP
(PROPANE) GAS IS HEAVIER THAN AIR,
TENDS TO SETTLE IN LOW AREAS. EVEN
THE SLIGHTEST SPARK CAN IGNITE THESE
GASES AND CAUSE AN EXPLOSION.
PROCEDURE:
A water manometer or a gauge that is calibrated in
"ounces per square inch" may be used to measure
the fuel pressure. Fuel pressure at the inlet side of
the fuel solenoid valve should be between 11 - 14
inches water column as measured with a manometer,
or 6.38-8.00 ounces per square inch as measured
with a pressure gauge.
The fuel pressure can be checked using a pressure
tester kit (Generac p/n 0C7977). See Figure 16 for
the gas pressure test point on the fuel regulator.
GAS PRESSURE TAP
FUEL HOSE
IDLE
CIRCUIT
PORT
ADJUSTER
SCREWS
Figure 16. Air Cooled Engine Fuel System
Page 104
BRASS
SMALL
HOSE
FUEL JET
FITTINGS
REGULATOR
HOUSING
PORT
PART 4
NOTE: Where a primary regulator is used to
establish fuel inlet pressure, adjustment of that
regulator is usually the responsibility of the fuel
supplier or the fuel supply system installer.
RESULTS:
1. If fuel supply and pressure are adequate, but engine will
not start, go on to Test 53.
2. If generator starts but runs rough or lacks power, repeat
the above procedure with the generator running and
under load. The fuel system must be able to maintain
11"-14" water column at all load requirements. If proper
fuel supply and pressure is maintained, go to Test 55.
TEST 52 - TEST FUEL SOLENOID
Note: This test is for fuel regulators equipped
with idle circuit port only. See Figure 16. These
units have an additional 1/4" fuel hose.
DISCUSSION:
When the Fuel Solenoid (FS) is energized, gas pres-
sure is available internally to the on demand Fuel
Regulator. Gas pressure will then be available to the
idle circuit port of the Fuel Regulator.
PROCEDURE:
1. Disconnect Wire 56 from the starter contactor relay
(SCR). This will disable the unit from cranking. For sin-
gle cylinder units, disconnect from the starter contactor
(SC) and isolate it from ground.
2. Remove the fuel hose from the idle circuit port barbed fitting.
3. Attach a manometer (Generac P/N 0C7977) to the idle
circuit port barbed fitting.
4. Set the AUTO-OFF-MANUAL switch to MANUAL. The
engine will not crank, but gas pressure should be
observed on the manometer at 11"-14" of water column.
5. Set the AUTO-OFF-MANUAL switch to OFF. Remove
the manometer. Re-attach the fuel hose to the idle cir-
cuit port barbed fitting. Re-connect Wire 56 to the
starter contactor relay or starter contactor.
RESULTS:
1. If gas pressure was measured, proceed to Test 55.
2. If gas pressure was NOT measured, replace the fuel
solenoid (FS).
TEST 53 - CHECK CIRCUIT BOARD WIRE 14
OUTPUT
DISCUSSION:
During any cranking action, the circuit board's crank
relay (K1) and run relay (K2) both energize simultane-
ously. When the run relay energizes, its contacts
DC CONTROL