Section 7.2

ENGINE DC CONTROL SYSTEM / AC TROUBLESHOOTING

ENGINE COMPRESSION PRESSURE

NOMINAL PRESSURE: 60 psi

MINIMUM ALLOWABLE: 55 psi

NOTE: Full compression pressure cannot be obtained at cranking speeds, due to the action of a compression release mechanism.

RESULTS:

If compression is poor, look for one or more of the fol- lowing possible causes:

1.Loose cylinder head bolts.

2.Failed cylinder head gasket.

3.Burned valves or valve seals.

4.Insufficient valve clearance.

5.Warped cylinder head.

TEST 27- TEST OIL TEMPERATURE SWITCH

DISCUSSION:

See Section 6.5, "ENGINE SHUTDOWN FEATURES.”

TEST PROCEDURE:

See Section 6.5.

RESULTS:

NOTE: The generator will shutdown if the 12-pin connector is disconnected and the circuit breaker is turned on. In order to perform the running diagnostic tests, you must jump pin #10 to pin #11. This will enable the unit to continue to run with the circuit breaker turned to the “ON” posi- tion (See Figure 10 on page 7.2-17).

6.Warped valve stem.

7.Worn or broken piston ring(s).

8.Worn or damaged cylinder bore.

9.Broken connecting rod.

TEST 26- TEST OIL PRESSURE SWITCH

DISCUSSION:

See Section 6.5, "ENGINE SHUTDOWN FEATURES.”

TEST PROCEDURE:

See Section 6.5.

If necessary, connect an external oil pressure gauge to the oil pressure switch port.

RESULTS:

1.Replace oil pressure switch if it is defective or repair Wire 85 circuit as necessary.

2.If oil pressure is actually low as indicated by the external gauge, see Section 5.1, "ENGINE OIL SYSTEM".

3.If oil pressure is good and oil pressure switch is good, go to Test 27.

TEST 28 - DC LINK VOLTAGE TEST

1.Disconnect the 12-pin connector from the inverter. Disconnect the Red-Black-Blue-Green DC Link wires from the inverter.

Note: Cap the DC Link wires with a wire nut for safety.

2.On units with A6060 circuit board revision “D” or higher soft- ware, jump pin #10 to pin #11 on the 12-pin cable previously removed from the inverter. The 12 position cable should be connected to the 12-pin socket on the generator control panel. This will enable the generator to run with CB1 turned ON.

3.Turn CB1 to ON position. Start generator. The engine should run at approximately 3300 rpm.

4.Set VOM to DC. Measure DC Link voltage between the Red and Blue wires, place Red test lead to red wire and Black test lead to the Blue wire. DC voltage should be approximately 375 VDC. Measure DC link voltage between the Red wire and Black wire, place Red test lead to Red wire and Black test lead to Black wire, DC voltage should read +175 VDC. Measure DC link voltage between the Blue wire and the Black wire, place Red test lead to Blue wire and Black test lead to Black wire. DC voltage should read –175 VDC.

Page 7.2-16

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Generac Power Systems 940-2, 941-2 service manual Test 27- Test OIL Temperature Switch, Test 26- Test OIL Pressure Switch
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941-2, 940-2 specifications

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