Generac Power Systems GTH760 Service Manual page 13

GENERAL INFORMATION
Generac GTH/GTV-760/990 OHVI V-Twin engines use a magneto
ignition: an ignition coil with a self-contained transistor module (no
moving parts). Two magneto ignition coils are used, with a flywheel
containing a permanent magnet.
NOTE: The magneto ignition system requires a minimum of 300
RPM to produce a consistent spark.
ENGINE WIRING HARNESS
The engine wiring harness consists of a ground wire with a diode for
each ignition coil and a separate wire for the carburetor solenoid. The
engine ground wires are connected to the wiring harness provided by
the equipment manufacturer.
NOTE: Models built after 2007 will have the diodes built into
the ignition coils or spark plug leads. Check the wire harness.
If there are no diodes in the harness, perform test on the coil
ground terminal.
See Figure 2-4.
TESTING GROUND WIRES:
Use a Digital Multimeter (Figure 2-1) to test the ground wires.
The following test will be made with the meter in the Diode Test posi-
tion.
In the Diode Test position, the meter will display the forward voltage
drop across the diode(s). If the voltage drop is less than 0.7 volts,
the meter will "Beep" once as well as display the voltage drop. A
continuous tone indicates continuity (shorted diode) An incomplete
circuit (open diode) will be displayed as "OL."
Figure 2-1. Digital Multimeter
1. Insert RED test lead into
2. Inser t BLACK test lead into the "COM" receptacle in meter.
3. Rotate selector to (Diode Test) position.
4. Insert RED test lead clip into connector "A" (Figure 2-2). Leave
receptacle in meter.
2-1
attached for remainder of test.
5. Touch BLACK test lead probe to terminal "B."
a. If meter "Beeps" once, diode is OK.
b. If meter makes a continuous tone, diode is defective (shorted).
Replace ground harness.
c. If meter displays "OL," diode is defective (open). Replace ground
harness.
6. Now repeat test for terminal "C." Results must be the same.
7. Replace wiring if defective.
8. If wiring tests good, proceed to IGNITION COILS section to replace
defective coil.
Note: See "Diode Failure Diagnosis", Figure 2-3.
ENGINE
GROUND
HARNESS
A
CYL #1
B
POSITIVE METER
TEST LEAD
Figure 2-2. Testing Ground Wire
SWITCH ON TURNED OFF
Engine Runs Shuts Off OK
On 1 Cylinder
Engine Runs Only One
(Both Cylinders) Cylinder
Won't Run
(No Spark)
Engine Runs Engine Won't Shut
(Both Cylinders)
Figure 2-3. Diode Failure Diagnosis
WIRE HARNESS CHECK
IGNITION COIL TESTING:
If ignition does not have spark, disconnect ground wire from ignition
SECTION 2: IGNITION
IGNITION
GROUND
C
WIRE STUD
CYL #2
NEGATIVE METER
TEST LEAD
CAUSE
1 Closed Diode
1 Open Diode
2 Closed Diodes
2 Open Diodes
Off
2