Principles of Automatic Engine Speed ​​Control and Fault Detection for the Caterpillar E240 Excavator

 1 Operating Principle of the AEC System

 

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 The AEC (Automatic Engine Control) system is an automatic throttle control system that limits the engine to high and low speed settings. It utilizes a worm gear mechanism to shift the throttle limit linkage, thereby controlling the engine speed: the throttle is set to the high-speed position during operation and to the low-speed position during no-load conditions.

 1.1 Acceleration When the control lever is moved, a hydraulic signal is transmitted to the AEC pressure switch (8), causing it to close. With the AEC switch (9) set to ON and the work mode switch (10) set to 

 position I (or II/III), three signals are input to the controller (7). After processing these signals, the controller outputs current to the AEC relay (6). The relay activates: normally open contact (a) closes, and normally closed contact (b) opens. A closed circuit is formed: Battery → Power Switch (2) → Fuse Box (3) → Limit Contact (c) → Relay Contact (a) → AEC Motor (5) Winding → Ground. Motor (5) rotates, driving the worm gear 180 degrees to push the throttle to the high-speed position, accelerating the engine to 2380 rpm. Due to the mechanical linkage of motor (5), once the high-speed position is reached, contact (c) opens and contact (d) closes; this breaks the circuit driving the motor's acceleration, causing the motor to stop while the engine throttle remains in the high-speed position. The engine then operates atits rated speed.

 1.2 Deceleration When the control lever returns to the neutral position, no hydraulic signal is sent to the AEC pressure switch (8), causing it to open. If switch (8) remains open for 3 seconds after the controller (7) receives this signal, the controller cuts off the output current to the SOL.B terminal. Relay (6) de-energizes; contact (a) opens, and normally closed contact (b) closes. 1 Current flows from the battery through contact d to contact b, then through the AEC motor 5 winding to ground, forming a closed circuit.

Motor 5 rotates, driving the worm gear to continue turning by 180° and pushing the throttle from the high-speed position to the low-speed position, thereby reducing the engine speed to 1300 r/min. Due to the mechanical linkage, contact d opens and contact c closes; this breaks the closed circuit that caused motor 5 to decelerate, causing motor 5 to stop operating. The engine then runs at low speed to conserve fuel.

 2 Fault Diagnosis Common faults in the automatic engine throttle control system of the Caterpillar E240 excavator include: 

 

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 (1) After the control lever returns to the neutral position, the engine throttle fails to automatically drop to low speed and remains in the high-speed position.

 (2) When the control lever is operated, the engine throttle fails to automatically accelerate and remains in the low-speed position. Based on the AEC system's circuit principles, fault diagnosis can be performed using the following steps:

 ① First, check whether the AEC motor and controller fuse in fuse box 3 has blown.

② Check the AEC pressure switch 8. When the engine is running and the control lever is in the operating position, the AEC pressure switch should be closed; when the control lever is in the neutral position, the AEC pressure switch should be open. If there is no response, first check the hydraulic signal. The signal oil pressure for the AEC pressure switch is the pilot oil pressure; during normal operation, the oil pressure should be between 4.25 and 4.55 MPa. When the control lever returns to the neutral position, the signal oil pressure drops to the return oil pressure level. The AEC pressure switch closes when the signal oil pressure is ≥2.45 MPa and opens when it is <2.45 MPa. If the detected signal oil pressure is normal but the AEC pressure switch shows no response, the switch is faulty and should be replaced. If the detected signal oil pressure is abnormal, further inspect the pressure in the signal oil circuit.  

 ③ Check the AEC switch (9), backup switch (4), and operating mode switch (10) for damage. Check the continuity of the corresponding contacts and look for any short-to-ground faults; replace if damaged.

 ④ Check the AEC relay (6). The AEC relay coil resistance is 170Ω; this can be measured. Check the closing and opening of the AEC relay contacts by directly applying and cutting off power. Replace if damaged.

 ⑤ Check the AEC motor (5). This can be tested by momentarily applying power: ground the 'i' wire and momentarily apply power to the 'f' wire; if the AEC motor operates, it is functional; otherwise, disassemble/inspect or replace it. Check the linked contacts 'c' and 'd': when the AEC motor is in the high-speed position, wires 'e' and 'h' should be connected (0Ω resistance) and wires 'e' and 'g' disconnected (infinite resistance); when the AEC motor is in the low-speed position, wires 'e' and 'h' should be disconnected (infinite resistance) and wires 'e' and 'g' connected (0Ω resistance). If these conditions are not met, inspect the contacts and the linkage mechanism.

 ⑥ Check the connections of all wires and plugs for open circuits or short circuits; ensure proper connection.

 ⑦ Test the controller (7). Measure the voltage parameters at the controller terminals according to Table 1. (Referred to as the AEC system).

 If the test results do not match specifications, it indicates internal damage to the controller's control circuitry (ECU board). Options include replacing the entire controller, using the backup switch for emergency operation, or modifying the AEC control system. 3 Emergency Modification of the AEC Control System

If a fault in the AEC motor relay control circuit of the Caterpillar E240 excavator engine throttle system is confirmed to be caused by an internal controller failure, a simple time-delay relay control circuit can be designed as an emergency measure. For the time-delay relay (7), a DS22C electromagnetic time-delay relay can be selected; specifications: 24V DC, normally open contact, adjustable delay range of 1.5–5 seconds. The DS22C relay is configured to cut off power after a 3-second delay, utilizing the controller's function for controlling the AEC relay; the delay setting is adjusted to the 3-second mark. A mounting bracket is fabricated to securely install the DS22C time-delay relay inside the electrical component box on the right side of the cab. The AEC pressure switch, AEC switch, AEC relay coil, controller fuse (e), cab lighting fuse (f), and DS22C time-delay relay are connected as shown in Figure 2, while all other existing wiring remains unchanged. It should be noted that this modification is limited to replacing the controller's function of controlling the AEC relay; all other original functions of the controller remain intact. Two units have been modified according to this scheme, yielding excellent operational results. The AEC function is implemented by installing a time-delay relay (7)—featuring a 3-second power-off delay—to replace the function of the controller (7) in controlling relay (6) as shown in Figure 1. 

 

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How to Address Power Loss in CAT Excavators

 Any engine will experience a drop in power output after prolonged use. This is primarily caused by the wear of key components—such as pistons, piston rings, and cylinder liners—resulting from extended operation; the standard remedy is to replace these parts. However, since specific conditions vary among manufacturers, users, and individual machines, the measures taken must be tailored to the specific 

 

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equipment to avoid unnecessary waste. The hydraulic system of a CAT excavator is supplied by a main pump driven by the engine; this main pump assembly consists of upper and lower sections, both of which are swash-plate type piston pumps. Each section features a regulator that adjusts the effective stroke of the pistons to increase or decrease displacement, thereby altering the pump's power absorption capacity. Over time, engine power output declines, and the swash-plate angle shifts, leading to a reduction in the pump's power absorption capacity; this significantly lowers the power absorbed by the hydraulic system.

 

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  Symptoms typically include slower boom lifting/lowering, arm extension/retraction, upper structure slewing, and travel speed. In such cases, the initial course of action should be to adjust the main pump regulator rather than performing a major engine overhaul. Since the pump's initial power absorption does not match the engine's maximum output—leaving a margin—and the pump does not operate at its limit initially, adjusting the regulator allows the pump's power absorption capacity to increase. This compensates for the decline in the pump's own absorption capacity as well as the shortfall in absorbed power caused by the drop in engine output. Such adjustments ensure that the power absorbed by the hydraulic system remains at or near normal operating levels, thereby maintaining the excavator's proper functionality. The main pump regulator on a CAT excavator typically features three adjustment screws: one for negative flow control pressure, one for power variation pressure, and one for the maximum swashplate angle. To avoid adjustments that might cancel each other out, one should never blindly turn these screws without understanding the relationship between the adjustment direction and the resulting change in power. The standard procedure is to adjust one screw at a time; once the relationship between its adjustment direction and the power change is determined, return that screw to its original position. Follow the same method to identify the power-change relationships for the other two screws. Finally, adjust all three screws in the direction that increases power output, thereby enhancing the hydraulic system's power absorption capacity. Practical experience shows that a CAT excavator adjusted in this manner can continue to operate reliably for another year; by the time the engine requires a major overhaul, the machine may

 

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 have logged over 20,000 operating hours, representing significant economic value. It should be noted, however, that this type of main pump regulator generally allows for only one such adjustment. If the hydraulic system subsequently experiences a noticeable drop in power, further adjustments usually yield poor results, indicating that a major engine overhaul is required.

How to Solve Low Oil Pressure Fault in Caterpillar Excavator 320C

  Many excavator operators report low oil pressure during operation.

Excavator Symptoms: Insufficient oil pressure leads to accelerated wear on the crankshaft and bearings, cylinder liners and pistons due to poor lubrication. 

 

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 Causes:

1. Insufficient oil level 

 2. Oil pump not running 

 3. Oil cooler leak 

 4. Malfunctioning pressure sensor or blocked oil passages 

5. Inappropriate oil grade 

Solutions: 

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1. Increase oil level.

 

 2. Disassemble and calibrate the oil pump, checking its wear condition. 

 

 3. Inspect the oil cooler. 

 

 4. Inspect the pressure sensor. 

 

5. Check if the oil grade is compatible with your machine.

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What should be done if the oil temperature on a Caterpillar 320C excavator becomes too high? How should this issue be handled?

 Many operators encounter the problem of "excessive oil temperature" during excavator operation.

 Excessive oil temperature can even trigger a series of issues, such as thermal deformation of mechanical 

parts and the seizing of moving hydraulic components—caused by reduced clearances resulting from 

differing coefficients of thermal expansion—which leads to operational malfunctions, impaired 

transmission precision in the hydraulic system, and degraded component performance.

 

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 Analysis of causes: 

1 The hydraulic oil has not been changed for an extended period. 

2 Hydraulic pump malfunction. 

3 Controller (ECU) malfunction or incorrect settings. 

4 Insufficient oil tank capacity or inadequate heat dissipation surface area; lack of an oil cooling system, 

or a cooling system with insufficient capacity.

 

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Solutions: 

1 If the hydraulic oil in your excavator has not been changed for over 6,000 hours, it must be replaced. 

2 Have the hydraulic pump inspected and adjusted by a professional. 

3 Reset or repair the electronic control unit (ECU). 

 

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How to Remove the Cylinder Head of a Caterpillar 320D2 Excavator

 Start: a. Remove the fine fuel filter, fuel filter holder, and bracket. For correct procedures, see Disassembly and Assembly, "Fuel Filter Holder - Removal and Installation".

 

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 b. Remove the oil-water separator, fuel pre-filter, and bracket. For correct procedures, see Disassembly and Assembly, "Oil-Water Separator and Fuel Pre-Filter - Removal and Installation". 

c. Remove the rocker arm shaft and pushrod. For correct procedures, see Disassembly and Assembly, "Rocker Arm Shaft and Pushrod - Removal". 

 d. Remove the exhaust manifold. See Disassembly and Assembly, "Exhaust Manifold - Removal and Installation" for the correct procedure. 

 e. Remove the crankcase breather filter canister and plastic tubing assembly. For correct procedures, see Disassembly and Assembly, "Crankcase Breather - Removal".

  f. Remove the fuel injectors. For the correct procedure, see Disassembly and Assembly, "Injector - Removal". 

 g. Remove the glow plug. See Disassembly and Assembly, "Glow Plug - Removal and Installation" for the correct procedure.

 1. Drain the coolant from the cooling system into a suitable container for storage or disposal. For the correct draining procedure, 

 ee the Operation and Maintenance Manual, "Cooling System Coolant - Replacement".

 see the Operation and Maintenance Manual, "Cooling System Coolant - Replacement". 

 

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 2. Disconnect the upper radiator hose from the water temperature regulator housing (1) on the cylinder head.

 

 

 

 

3. Loosen the hose clamps and then disconnect the hose assembly and hose assembly from the connector (11). 

 4. Remove bolt (3) and then remove bracket (2) from the cylinder head. 

 5. Remove bolts (4) and (9) from brackets (5) and (10). 

6. Disconnect the plastic tube assembly (6) and plastic tube assembly (8) from the fuel injection pump (7)

. 7. Use tool (A) to plug the plastic tube assembly (6) and plastic tube assembly (8). 

 8. Use tool (A) to cover the connector of the fuel injection pump (7). 

 9. If necessary, remove the tube assembly from the cylinder head and the boost control of the fuel injection pump. For correct procedures, see Disassembly and Assembly, "Fuel Injection Pump - Removal (with Boost Control)". 

10. Remove bolt (12) from the clamp of the tube assembly (13). 

 11. Remove bolt (14) from the bypass pipe (15). 

12. Remove the bypass pipe (15) from the cylinder head. 13. Remove O-rings (16) and (17) from the bypass pipe (15). 14. Loosen bolts (18) in the reverse numerical order of tightening. See Illustration 6.

 Note: Following the correct order helps prevent cylinder head deformation.

 15. Remove bolts (18) from the cylinder head (19). 

 

 16. Attach suitable lifting equipment to the cylinder head (19). Support the weight of the cylinder head. The cylinder head weighs approximately 96 kg (212 lb).

 

  Note: During lifting, a strut must be used to distribute the weight of the cylinder head.

 17. Use suitable lifting equipment to lift the cylinder head (19) away from the cylinder block.

 Note: Do not use levers to separate the cylinder head from the cylinder block. Take care not to damage the machined surfaces of the cylinder head during disassembly.

 

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 18. Remove the cylinder head gasket (21). 

 19. Record the position of the locating pin (20) in the cylinder block. 

 20. If necessary, remove the water temperature regulator from the cylinder head. For correct procedures, see Disassembly and Assembly, "Water Temperature Regulator - Removal and Installation".

How to disassemble and install the Caterpillar 320D2 Excavator DNP intake and exhaust valve guides

 Start: a. Remove the intake and exhaust valves. See Disassembly and Assembly, "Intake and Exhaust Valves - Removal and Installation".

 

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 Note: Valve guides and valve seats must be removed by a properly trained professional. Specialized machinery is also required. For more information,

 Note: Keep all parts clean and free of contaminants. Contaminants cause rapid wear and shorten component life.

 

 

Use appropriate presses and tools (A) to remove the valve guide (2) (not shown) from the cylinder head (1).

 

2. Repeat step 1 for the remaining valve guides. 

 

Note: Valve guides and valve seats must be removed by a properly trained professional. Specialized 

machinery is also required. For more information, 

 

Note: Keep all parts clean and free of contaminants. Contaminants cause rapid wear and shorten 

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component life. 1. Clean the valve guide bore in the cylinder head. 

 

 

2. Lubricate the new valve guide (2) with clean engine oil. Position the valve guide (2) in place on the cylinder head (1).

 
Carefully tap the valve guide to begin installation.  

 

3. Use appropriate presses and tools (A) to install the valve guide into the cylinder head. 

 

4. Repeat steps 2 through 3 for the remaining valve guides.  

 

 5. Check the protrusion (X) of the valve guide (2). The valve guide should protrude 12.7 mm (0.500 in) above the valve spring recess.

 

 

For more information, see the technical specifications, "Cylinder Head Valves".  

 

6. After installing the valve guide (2), the valve guide must be enlarged, and the valve seat insert must be cut to the finishing diameter. Follow steps 6.a through 6.d to ream the large valve guide and cut the valve seat insert. 

a. Lubricate the bore of the valve guide (2) with clean engine oil. 

 

b. Ream the large valve guide using tool (B). Ensure even pressure is applied to tool (B). 

 

c. Cut the valve seat using tool (B). Ensure even pressure is applied to tool (B). 

 

d. Ensure the cylinder head is clean and free of machining debris.

 

7. Check the finishing diameter of the valve guide (2). For more information, see Technical Specifications, "Cylinder Head - Valve".    

 

8. Check the depth of the valve below the cylinder head surface. For more information, see System Operation, Testing and Adjustment, "Valve Depth - Check". 

 

End: a. Install the intake and exhaust valves. See Disassembly and Assembly, "Intake and Exhaust Valves - Removal and Installation".  

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How to Install Caterpillar 320D2 Excavator Intake and Exhaust Valves

  Installation Steps

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  Note: Keep all parts clean and free of impurities.

  Impurities will cause rapid wear and shorten component life.

 Note: The valve hard surfaces have been polished. Do not use abrasives on the valves. Abrasives will damage the valve hard surface polishing.

  1. Clean all parts of the cylinder head assembly. Ensure that all openings, coolant passages, and lubrication passages in the cylinder head are free of debris. Inspect the cylinder head assembly parts according to steps 1.a through 1.e. Replace any damaged or worn parts.

 a. Inspect the cylinder head for wear or damage. For correct procedures, see System Operation, Testing, and Adjustment, 

 "Cylinder Head Inspection".

 b. Inspect the valve seats for wear or damage. For more information, see the technical specifications, "Cylinder Head Valves".

 c. Inspect the valve guides for wear or damage. For more information, please refer to the Technical Specifications, "Cylinder Head Valves" and System Operation, Testing and Adjustment, "Valve Guides - Inspection". 

 d. Inspect the valves for wear or damage. For more information, please refer to the Technical Specifications, "Cylinder Head Valves".

 e. Inspect the valve springs for wear and for correct length. For more information, please refer to the Technical Specifications, "Cylinder Head Valves".

 

  2. Lubricate the valve (5) stems with clean engine oil. Install the valve (5) in its appropriate position on the cylinder head. Check the depth of the valve below the cylinder head surface. For more information, please refer to System Operation, Testing and Adjustment, "Valve Depth - Inspection".

 3. Use appropriate lifting equipment to flip the cylinder head. The cylinder head weighs approximately 96 kg (212 lb).

 Note: Ensure all valves remain in place.

 4. Install the new valve stem seals (4) onto the individual valve guides. The intake and exhaust valve stem seals are different and can be distinguished using color markings.

 

Note: The outer surface of the valve guide must be clean and dry before installing the valve stem seal (4).

 

 

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  5. Install the valve spring (3) onto the cylinder head. Place the valve spring seat (2) onto the valve spring (3).

 Warning: Being struck by parts propelled by the spring force can cause personal injury.

  Ensure you wear all necessary protective equipment.

 Follow the recommended procedure and use all recommended tools to release the spring force.

  6. Install tool (A) in the appropriate position on the cylinder head to compress the valve spring (3).

  Caution: Ensure the valve spring is compressed evenly at all four corners; otherwise, damage to the valve stem may occur.

 7. Apply sufficient pressure to tool (A) to install the valve retainer (1).

 

 Note: When compressing the spring, do not allow the valve spring seat (2) to contact the valve stem seal (4).

  Warning

When the valve spring compressor is released, the valve spring retainer will pop out of the valve. Ensure

The valve spring retainer is correctly installed on the valve pushrod. To prevent personal injury, keep away from the front of the valve spring retainer and the valve spring when installing the valve.  

 8. Carefully release the pressure on tool (A). 

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 9. Repeat steps 5 through 8 for the remaining valves. 

10. Remove tool (A) from the cylinder head.

  End: a. Install the cylinder head. For correct procedures, see Disassembly and Assembly, "Cylinder Head - Installation".