3512B Engine for SPF343, SPS343, and SPT343 Pumpers Caterpillar

The engine speed control provides a primary throttle signal to the engine's Electronic Control Module (ECM). The output for rated speed is a pulse width modulated signal. The signal varies with the position of the "Deck RPM Control" potentiometer. The output signal is expressed as a percentage between 0 and 100 percent for the speed adjust potentiometer.

The ECM calculates the desired engine speed. The desired engine speed is produced by the signal from the rated speed setting. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the rated speed signal is invalid, the engine will be set to low idle.

Illustration 1	g00855250
Typical example

Test Step 1. Check for Connector Damage.

1. Turn the circuit breaker CB-8 to the OFF position.

2. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

4. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

5. Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

6. Check the harness and the wiring for abrasion and pinch points.

Expected Result:

The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

• OK - The wiring and connectors are okay. Proceed to test step 2.

• Not OK - The wiring and/or connectors need repair.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.

Test Step 2. Check the Voltage at the Speed Control.

1. Turn the circuit breaker CB-8 to the ON position.

2. Connect the red probe of the digital multimeter to the + Battery terminal of the Speed Control. Connect the black probe of the digital multimeter to the - Battery terminal of the Speed Control.

Expected Result:

The voltage should read 24 ± 3 VDC.

Results:

• OK - The voltage is 24 ± 3 VDC. The voltage supply to the Speed Control is correct. Proceed to test step 3.

• Not OK - The voltage does not read 24 ± 3 VDC.

  Repair: There is a problem with the supply voltage to the Speed Control. Check that circuit breaker CB-8 is turned on. Check the wiring and/or connectors from the + Battery terminal of the speed control to the Battery.

  Stop.

Test Step 3. Check the Throttle Position.

1. Turn the circuit breaker CB-8 to the OFF position.

2. Start the Caterpillar Electronic Technician (ET).

3. Open the circuit for the Fuel Cutout.

4. Turn the circuit breaker CB-8 to the ON position.

5. Observe the position of the throttle on the Cat ET.

6. Turn the "Deck RPM Control" potentiometer to the lowest setting.

7. Start at the low idle position. Slowly turn the "Deck RPM Control" potentiometer in the other direction. Monitor the position of the throttle on the Cat ET.

Expected Result:

The Throttle Position on the Cat ET should read 0 percent at the lowest setting and 0 to 100 percent as the "Deck RPM Control" potentiometer is adjusted.

Results:

• OK - The Speed Control is operating correctly.

  Repair: The problem may be intermittent. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

• Not OK - The throttle position on Cat ET does not correspond to adjustments of the "Deck RPM Control" potentiometer. Proceed to test step 4.

Test Step 4. Check the "Deck RPM Control" Potentiometer.

1. Turn the circuit breaker CB-8 to the OFF position.

2. Remove the wire from the S terminal at the speed control.

3. Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

4. Place one probe of the multimeter on the S terminal of the speed control. Place the other probe on the - Battery terminal of the speed control.

5. Turn the circuit breaker CB-8 to the ON position.

6. Turn the "Deck RPM Control" potentiometer to the lowest setting.

7. Start at the low idle position. Slowly turn the "Deck RPM Control" potentiometer in the other direction.

8. Monitor the output of the percent duty cycle from the S terminal of the speed control. Turn the "Deck RPM Control" potentiometer from the low setting to the high setting.

   Note: The throttle position on the Cat ET will NOT match the percent duty cycle on the multimeter.

9. Turn the circuit breaker CB-8 to the OFF position.

10. Reconnect the wire that was removed from the S terminal.

Expected Result:

The Duty Cycle should be between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting.

Results:

• OK - The Duty Cycle is correct. Proceed to test step 5.

• Not OK - The Duty Cycle is not correct on the multimeter.

  Repair: Install another "Deck RPM Control" potentiometer. Verify that the problem is no longer present. If the problem is still present, replace the speed control. Reinstall the old "Deck RPM Control".

  Stop.

Test Step 5. Check the Input to the ECM from the Speed Control.

1. Turn the circuit breaker CB-8 to the OFF position.

2. Remove ECM connector P2.

3. Remove the signal wire for the primary throttle from P2-24.

4. Reconnect ECM connector J2/P2.

5. Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

6. Place one probe of the multimeter on the signal wire for the primary throttle from P2-24. Place the other probe on the - Battery terminal of the speed control.

7. Turn the circuit breaker CB-8 to the ON position.

8. Turn the "Deck RPM Control" potentiometer to the lowest setting.

9. Start at the low idle position. Slowly turn the "Deck RPM Control" potentiometer in the other direction.

10. Monitor the output of the percent duty cycle from the signal wire for the primary throttle from P2-24. Turn the "Deck RPM Control" potentiometer from the low setting to the high setting.

11. Turn the circuit breaker CB-8 to the OFF position.

12. Reconnect all wires and connectors.

Expected Result:

The Duty Cycle should be between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting.

Results:

• OK - The Duty Cycle is correct.

  Repair: Recheck the Throttle Position on the Cat ET. There may be an intermittent problem. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details. If the connectors and wiring are okay and the Throttle Position on the Cat ET is not correct, replace the ECM. Perform the diagnostic procedure Troubleshooting, "Replacing the ECM".

  Stop.

• Not OK - Duty Cycle - The Duty Cycle is not correct.

  Repair: There is a problem in the wiring between P2-24 and the S terminal of the "Deck RPM Control" potentiometer. Verify that the low idle switch is functioning properly.

  Stop.