Guardian 4721, Repair Manual, Page: 94 / 115

TEST 18 - CHECK DC VOLTS AT TERMINAL 14
OF TB1
DISCUSSION:
This test will determine if control board action is deliv-
ering battery voltage to the Wire 14 circuit. Wire 14
circuit voltage is required to (a) power the engine igni-
tion system and (b) open the fuel solenoid. Terminal
board TB1 is housed in the generator control console.
See “Control Console Components” in Section 4.1).
PROCEDURE:
1. Use a DC voltmeter (or VOM) to check for battery voltage
at Terminal 14 of terminal board TB1.
2. Connect the positive (+) meter test lead to Terminal 14,
the common (-) test lead to Terminal 0 (ground).
3. Set the AUTO-OFF-MANUAL switch to MANUAL. The
meter should indicate battery voltage.
RESULTS:
1. If battery voltage is not indicated, test Wire 14 between
terminal board TB1 and the control board for an open
condition.
a. If Wire 14 is good, replace the control
board.
b. If Wire 14 is bad, repair, reconnect or
replace as necessary.
2. It battery voltage is indicated, go to Test 22.
TEST 19 - TEST FUEL SOLENOID (FS)
DISCUSSION:
The fuel solenoid is opened by 12 volt DC power from
Wire 14 and from the control board.
Figure 15. Fuel Solenoid (FS)
PROCEDURE:
1. Connect a DC voltmeter (or VOM) across Wire 14 at the
fuel solenoid and frame ground.
2. Set the AUTO-OFF-MANUAL switch to MANUAL. The
engine should crank and start. The meter should indicate
battery voltage. The fuel solenoid should energize.
RESULTS:
1. If battery voltage is indicated but the fuel solenoid does
not energize, replace the solenoid.
2. If the fuel solenoid is good, go on to Test 23.
TEST 20 - CHECK ENGINE COMPRESSION
AND CONDITION
DISCUSSION:
If the engine cranks but will not start, or if it starts
hard and runs rough, one possible cause of the prob-
lem is a mechanical failure in the engine.
PROCEDURE:
1. Warm up the engine.
2. Shut engine down and remove all spark plugs.
3. Use an automotive type compression tester to check
engine compression.
NOTE: When checking compression, hold the car-
buretor throttle wide open. Then, crank engine
and read the compression pressure.
4. Compression pressure should be as follows:
Standard = 160 psi (12.1 kg/cm2) at 350 rpm
Minimum = 120 psi (8.4 kg/cm2) at 350 rpm
Difference between cylinders should not exceed
15 psi (1.1 kg/cm2)
If compression is low in any cylinder, pour a small
amount of clean engine oil into the spark plug opening.
Then, retest compression and evaluate as follows:
• If compression pressure increases after adding the
oil, check for worn or damaged piston rings.
• If compression pressure did NOT increase after
adding the oil, check for sticking or improperly seat-
ed valves.
• If compression in any two adjacent cylinders is low
and adding oil did NOT increase the compression
pressure, check for a leaking head gasket
14
0
FUEL SOLENOID
GROUND
+
_
FUEL REGULATOR
PART 4
Page 90
DC CONTROL
LIQUID COOLED
ENGINE UNITS
SECTION 4.4
DIAGNOSTIC TESTS