Test 59 - Check Shutdown Wire - Generac Power Systems 7 kW NG Repair Manual

Section 4.5
Diagnostic Tests
Note: Refer to Manufactures instructions for variations of
this procedure.
Procedure
1. Remove both spark plugs.
2. Insert a compression gauge into either cylinder.
3. Crank the engine until there is no fur ther increase in
pressure.
4. Record the highest reading obtained.
5. Repeat the procedure for the remaining cylinder and
record the highest reading.
Results
The difference in pressure between the two cylinders should not
exceed 25 percent. If the difference in compression is greater
that 25 percent, loss of compression in the lowest reading
cylinder is indicated.
Example 1: If the pressure reading of cylinder #1 is 165
PSI and of cylinder #2 is 160 PSI. The difference is 5 PSI.
Divide "5" by the highest reading (165) to obtain the percent-
age of 3.0 percent.
Example 2: If the pressure reading of cylinder #1 is 160
PSI and of cylinder #2 is 100 PSI. The difference is 60
PSI. Divide "60" by the highest reading (160) to obtain the
percentage of 37.5 percent. Loss of compression in No. 2
cylinder is indicated.
If compression is poor, look for one or more of the following
causes:
• Loose cylinder head bolts
• Failed cylinder head gasket
• Burned valves or valve seats
• Insufficient valve clearance
• Warped cylinder head
• Warped valve stem
• Worn or broken piston ring(s)
• Worn or damaged cylinder bore
• Broken connecting rod
• Worn valve seats or valves
• Worn valve guides
TEST 59 – CHECK SHUTDOWN WIRE
Discussion
The controller uses Wire 18 for two purposes: first, to measure
engine RPM; second to shutdown the engine. The controller's
logic during a shutdown will apply a ground to Wire 18. Wire
18 is connected to the Ignition Magneto(s). The grounded
magneto will not be able to produce spark.
Procedure
1. On V-twin generators, (refer to Figure 140) remove Wire
18 from the stud located above the oil cooler. On single
cylinder generators, (refer to Figure 141) disconnect Wire
18 at the bullet connector.
Page 130
PART 4
WIRE 18 CONNECTION
Figure 140. Wire 18 Connection 10-20kW Units
WIRE 18
CONNECTION
Figure 141. Wire 18 Connection 8kW Units
2. Depending on engine type, do the following:
a. On V-twin units, remove Wire 56 from the star ter
contactor relay (SCR). Utilizing a jumper wire, jump 12
VDC from the positive battery terminal to the terminal
on the SCR from which Wire 56 was removed. The
generator will start cranking. As it is cranking, repeat
Test 55 – "Check for Ignition Spark." Reconnect Wire
56 when done.
b. On single cylinder units, connect a jumper wire from
the stud to which Wire 56 is connected on the starter
contactor (SC) and 12 VDC from the positive battery
terminal. The generator will start cranking. As it is
cranking, repeat Test 55.
3. With Wire 18 removed, if spark is now present, proceed to
check for a short to ground (Steps 4 through 7).
4. Disconnect the J4 connector from the controller.
5. Set the Volt-Ohm-Milliammeter (VOM) to measure
resistance.
6. Connect one meter test lead to Wire 18 (disconnected in
Step 1) and connect the other meter test lead to a clean
frame ground, measure and record the resistance.
7. Reconnect disconnected wires and connectors.
ENGINE/DC CONTROL