Use this procedure to determine if the Electronic Control Module (ECM) is properly controlling the fuel rack.
The engine is electronically controlled by the ECM. The ECM senses the engine rpm by using the engine speed sensor. The ECM controls the fuel rack by adjusting the voltage to the Rack Solenoid. Refer to Troubleshooting, "System Overview" for more information.
The following variables are used in this test. These variables will be displayed on the electronic service tool.
- Desired engine rpm is an input to the electronic governor within the ECM. Desired engine speed is based on throttle inputs, the engine speed sensor's signal and customer specified parameters.
- The desired rack position indicates the position of the rack in order to maintain the desired engine rpm. The desired rack position will not exceed the rack control for the fuel ratio. Also, the desired rack position will not exceed the rated rack limits.
- The ECM receives a signal from the rack position sensor. The ECM uses this signal to calculate the actual rack position. The ECM uses the rack position sensor signal as feedback to allow precise control of the rack position. The actual rack position follows the desired rack position if the rack controls are functioning properly.
- The rack control for the fuel ratio limits the fuel to the air ratio. The limit is used to reduce black smoke during acceleration. When the ECM senses a higher inlet manifold pressure, the rack control for the fuel ratio is increased in order to allow more fuel.
- The rated rack is a limit on the rack position that provides the specified power and torque curves. The rated rack is programmed into the personality module.
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| Illustration 1 | g01634937 |
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| Illustration 2 | g01635554 |
(10) + 8 VDC (22) Solenoid ground (23) Rack solenoid (30) + 5 VDC (35) Analog return (40) Rack position | |
Test Step 1. Inspect the Electrical Connectors and the Wiring Harness
- Remove electrical power from the ECM.
- Thoroughly inspect the J6/P6 connector for the rack solenoid (BTM) and the J11/P11 connector for the rack position sensor. Inspect the ECM connector J14/P14. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.
- Check the allen head screw on the ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points. Proceed to Test Step 2.
- NOT OK - There is a problem with the connectors and/or the wiring.
Repair: Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.Verify that the repair eliminates the problem.
STOP
Test Step 2. Verify Normal Rack Operation at Idle
- Connect a Caterpillar Electronic Technician (ET) to the service tool connector.
- Start the engine.
- Monitor the desired engine rpm, the desired rack position and the actual rack position on Cat ET.
Note: A lag in Cat ET may cause differences in the displayed values for the desired rack position and the actual rack position. For a typical engine at low idle with normal accessory loads, the desired rack position and the actual rack position is approximately 4.50 mm (0.18 inch) to 5.25 mm (0.20 inch).
Expected Result:
The desired engine rpm should equal the programmed low idle setting and the rpm should remain steady. The actual rack position should follow the desired rack position within ± 0.5 mm (± 0.02 inch).
Results:
- OK - The desired engine rpm is equal to the programmed low idle setting and the rpm remains steady. The actual rack position follows the desired rack position within ± 0.5 mm (± 0.02 inch). Proceed to Test Step 3.
- NOT OK - The desired engine rpm is unstable or too high.
Repair: Refer to Troubleshooting, "Speed Control - Test".
STOP
- NOT OK - The rack is not functioning properly.
Repair: Refer to Troubleshooting, "Sensor Signal (Analog, Active) - Test".
STOP
Test Step 3. Verify Normal Rack Operation Under Load
- Connect Caterpillar Electronic Technician (ET) to the service tool connector.
- Start the engine.
- Apply a load to the engine.
- Monitor the desired rack, the rated rack and the rack control for the fuel ratio on Cat ET.
Expected Result:
The desired rack reaches the rated rack when the engine is fully loaded.
Results:
- OK - The desired rack reaches the rated rack when the engine is fully loaded.
Repair: The rack operation is working properly. Refer to Troubleshooting, "Electrical Connectors - Inspect" for a intermittent problem.
STOP
- NOT OK - The desired rack is limited to the rack control for the fuel ratio which indicates low boost pressure.
Repair: Refer to Troubleshooting, "Inlet Manifold Pressure - Test" for further information.
STOP
- NOT OK - The desired rack is limited to a value below the rated rack.
Repair: The ECM may be limiting engine power or rpm. Refer to Troubleshooting, "Engine Top Speed Is Not Obtained" for further information.
STOP