Test 50 - Check Fuel Supply And Pressure - Generac Power Systems G0070420 Diagnostic Repair Manual

Results
If battery voltage is indicated on the meter but
1.
starter motor did not operate, remove and bench
test the starter motor.
If battery voltage was indicated and the starter
2.
motor tried to engage (pinion engaged), but engine
did not crank, check for mechanical binding of the
engine or rotor.
If engine turns over slightly, go to
3.
and Adjust Valves. If valve clearance is too loose
the valves will not fully open which could slow
down cranking of the engine.
Checking The Pinion
See Figure 3-31. When the starter motor is activated, the
pinion gear (A) should move and engage the flywheel
ring gear. If the pinion does not move normally, inspect
the pinion for binding or sticking.
Figure 3-31. Check Pinion Gear Operation
Test 50 – Check Fuel Supply and
Pressure
General Theory
The air-cooled generator was factory tested and adjusted
using natural gas as a fuel. If desired, LP (propane) gas
may be used. However, when converting to propane,
some minor adjustments are required. The following
conditions apply for a unit to operate correctly:
•
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 3.5 inches water
column for natural gas (NG) or 10 inches water
column for LP gas.
•
Maximum gaseous fuel pressure at the generator
fuel inlet connection is 7 inches water column for
natural gas or 12 inches water column for LP gas.
•
When propane gas is used, only a "vapor
withdrawal" system may be used. This type of
system utilizes the gas that forms above the liquid
fuel. The vapor pressure must be high enough to
ensure engine operation.
•
The gaseous fuel system must be properly tested
for leaks following installation and periodically
thereafter. No leakage is permitted. Leak test
methods must comply strictly with gas codes.
Diagnostic Repair Manual
Test 63 – Check
A
002403
002403
DANGER
Explosion and fire.Fuel and vapors are extremely
flammable and explosive. No leakage of fuel is
permitted. Keep fire and spark away. Failure to do
so will result in death or serious injury.
Procedure
A water manometer or a gauge that is calibrated in
"inches of water column" should be used to measure the
fuel pressure. Fuel pressure at the inlet side of the fuel
solenoid valve should be between 3.5-7 inches water
column for natural gas (NG), or 10-12 inches water
column for LP gas.
See Figure 3-32 for the gas pressure test point on
1.
the fuel regulator. The fuel pressure can be
checked at Port 1 (A) on all fuel regulators.
With the manometer connected properly, crank the
2.
engine. Nominal
measured. If pressure is not measured while
cranking refer back to flow chart.
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.
Figure 3-32. Gas Pressure Test points
NOTE: The static pressure port (before solenoid) is
ALWAYS closest to the solenoid.
Test Port 2 (B) below the fuel solenoid may be used to take
a fuel pressure reading before the fuel solenoid. Consistent
pressure should be measured at this port both while the
generator is running and when the generator is off.
Results
If fuel supply and pressure are adequate, but
1.
engine will not start refer back to the flow chart.
If generator starts but runs rough or lacks power,
2.
repeat the above procedure with the generator
running under load. The fuel supply system must be
able to maintain proper pressure. If proper fuel
supply and pressure is maintained, refer to
18 – Engine Starts Hard and/or Runs Rough /
Lacks Power / Backfires / Hunting / Erratic
Operation Flow Chart.
Section 3.5 Diagnostic Tests
(000192)
fuel pressure should
A
B
003273
Problem
be
75