Wheel Loader Signature Test 992G
Test 4: Converter Stall Test
The purposes of these tests are to record the engine performance and the steady state operating conditions against a torque converter stall.
Note: Do not apply the parking brake during the converter stall test. On VIMS equipped machines,
applying the parking brake with the transmission in gear will cause a category 3 parking brake-warning message to lock on the message center. This condition will prevent the serviceman from observing when the category 2 warning occurs from hot converter oil temperature during the stall test.
1. Chock the wheels to prevent movement of the machine, and lower the bucket to the ground. 2. Turn on the data logger.
3. At low idle, apply the service brakes and shift the transmission to 3rd speed forward. 4. Raise the engine speed to about 1200 RPM and hold until torque converter oil temperature
reaches 210°F.
5. Reduce the engine speed to low idle and shift the transmission to neutral for 3 to 5 seconds. 6. Apply the service brake and shift the transmission to the highest forward gear available. 7. Quickly accelerate engine speed from low idle to maximum speed.
8. Hold for 5 -10 seconds at maximum engine speed or until the torque converter oil temperature triggers a category 2 warning (250°F approx).
9. Reduce the engine speed to low idle, and shift the transmission lever to neutral.
10. Raise engine speed to about 1300 RPM and hold until the torque converter temperature cools to 210°F.
11. Reduce engine speed to low idle. 12. Repeat steps 4 through 10.
13. Turn off data logger and allow the system to cool to normal ranges. The engine should idle for at least one minute to let the turbochargers slow down.
Important data being electronically recorded by VIMS • Engine speed
• Torque converter temperature
• Turbo outlet pressure (Boost pressure) • Right and left exhaust temperatures
Test 5: Double Stall Test
The purposes of these tests are to record the engine performance and the steady state operating
conditions against a torque converter stall and an implement hydraulic stall. When measuring the engine response, accelerating the engine speed should occur first. If the implements and transmission were stalled before increasing the engine speed, the engine would stall.
Note: Do not apply the parking brake during the converter stall test. On VIMS equipped machines,
applying the parking brake with the transmission in gear will cause a category 3 parking brake- warning message to lock on the message center. This condition will prevent the serviceman from observing when the category 2 warning occurs from hot converter oil temperature during the stall test.
1. Chock the wheels to prevent movement of the machine. 2. Position the lift arms at the top of their travel.
3. Turn on the data logger.
4. At low idle, apply the service brakes and shift the transmission to the highest forward gear available.
5. Raise the engine speed to about 1200 RPM and hold until the torque converter oil temperature reaches 210°F.
6. Reduce the engine speed to low idle and shift the transmission to neutral for 3 to 5 seconds.
7. Apply the service brake, and quickly accelerate engine speed from low idle to maximum speed. 8. Shift the transmission into the highest forward gear available and move the lift control lever to the
full RAISE position.
9. Hold for 5 -10 seconds at maximum stall speed or until the torque converter oil triggers a category 2 warning (250°F approx).
10. Move the lift control lever to HOLD, shift the transmission lever to neutral, and reduce the engine speed to about 1300 RPM and hold until the torque converter temperature cools to 210°F. 11. Repeat steps 6 through 10.
12. Turn off data logger and allow the system to cool to normal ranges. The engine should idle for at least one minute to let the turbochargers slow down.
Important data being recorded electronically by VIMS • Engine speed
• Torque converter temperature • Hydraulic oil temperature
• Right and left exhaust temperatures. • Turbo outlet pressure (boost pressure).
Test 6: Impeller Clutch Pressure Test
The purpose of these tests is to record the steady state operating pressures of the impeller clutch versus the left pedal position at various engine speeds. For both of these tests, the reduced/max rimpull enable switch should be set to the MAX position.
Test 6a: Impeller Clutch Pressure vs. Left Pedal Position
1. Lower the bucket to the ground, and increase engine speed to high idle. 2. Turn on the data logger.
3. Leave the transmission in neutral and gradually increase the left pedal from 0% to 100%. Hold at 100% for 5 seconds, and gradually decrease pedal back to 0%.
4. Repeat step 3. 5. Turn off data logger.
Test 6b: Impeller Clutch Pressure vs. Engine Speed
1. Turn on data logger.
2. With transmission in neutral and engine speed at low idle, gradually increase engine speed from low to high idle in 15 seconds. Hold at high idle for 10 seconds.
3. Return engine speed to low idle for 10 seconds. 4. Repeat step 2.
5. Turn off data logger.
6. Download and clear the data logger.
Important data being recorded electronically by VIMS • Impeller clutch pressure and current
• Engine speed • Left pedal position
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Analysis of Signature Test Data
The following information is the recommended action to analyze the results from the signature tests on the 992G. Note the specific examples cited in this analysis section are results obtained from one 992G and results will vary between different machines. Acceptable operating ranges for these tests can be located in the appropriate service manuals for the 992G.
Stationary Tests
Test 1: Brake System Testing and Operating Temperatures
Operating Temperatures and Machine InformationThis test was performed to warm the machine to normal operating temperatures for later tests, and to determine if the brake system is functional. If the loader creeps forward during the brake tests, schedule necessary repairs to the brake system. The following machine information and operating temperatures can be recorded in the tables to record conditions for each signature test. This allows repeatability each time the signature test is run.
Machine Information Site: Model: Unit: Serial #: Operating Temperatures Test Date Ambient Air Temp Engine Coolant Temp T/C Out Temp Implement Oil Temp Atm Pressure Operating Range N/A 175-200°F 190-230°F 120-190°F N/A
Test 2: Unloaded Engine Tests
Engine Oil PressureEngine oil pressure versus engine speed data can be derived from this test. The engine speed is set at various points to record the steady state engine oil pressure at each speed. The engine speed versus oil pressure relationship can be verified by slowly raising engine speed from low to high. Figure 1 shows a typical run.
This data can be combined to provide a plot of engine oil pressure versus engine speed. Figure 2 was generated by extracting the data from Figure 1. The steady state oil pressure data is recorded in Table 1.
The straight-line curve in Figure 2 represents the oil pressure versus engine speed warning level that is used by the Engine Control Module and VIMS to provide low oil pressure warning. Oil pressure is checked against these curves according to engine speed.
A change in slope of the measured oil pressure occurs at an engine speed where the relief valve is beginning to open. The oil pressure increases slightly as engine speed increases until the relief valve is fully opened. On this machine, the relief valve is set to open at 83 psi, so the relief valve never opened in this test.
If the oil temperature and viscosity grade is the same, and there are significant changes in oil pressure, determine the reason and make repairs as needed.
Table 1: Oil Pressure vs. Engine Speed
Engine Speed 750 RPM 1000 RPM 1200 RPM 1400 RPM 1600 RPM 1675 RPM
Oil Pressure 57 psi
393 Kpa 62 psi 427 Kpa 65 psi 448 Kpa 67 psi 462 Kpa 70 psi 483 Kpa 71 psi 490 Kpa 8
Possible Reasons for Oil Pressure Changes:
1. Oil level very low. 2. Plugged oil filters.
3. Diesel fuel in lubrication oil.
4. Too much clearance between rocker arm shaft and rocker arms. 5. Oil pump suction pipe has a defect.
6. Oil pressure relief sticks open.
7. Oil pump or scavenge oil pump is worn.
8. Too much clearance between crankshaft and crankshaft bearings. 9. Too much clearance between camshaft and camshaft bearings. 10. Failed oil pressure sensor.
Engine Performance The 2nd portion of the unloaded engine test measures the engine response under no-load
conditions. The engine speed is quickly accelerated from low to high idle. The engine response is shown in Figure 3 and the results are recorded in Table 2. The engine response time is measured from the initial throttle input to the time the engine reaches high idle. It is difficult to measure the exact response time because the data is only collected at a one Hertz (once per second) sample rate. The low and high idle engine speeds are recorded on this graph for reference. The engine response time and steady state idle speeds should not significantly change over the engine life. If these parameters do significantly change, further investigation and testing of the engine is warranted.
Table 2: Typical Steady State Values for Engine Speed
Low Idle High Idle
750 RPM + 25 RPM 1675 RPM + 25RPM
Test 3: Hydraulic Tests
Cycle TimesThe lift cylinder cycle times are recorded in this test to give an indication of pump health. Figures 4 and 5 respectively show the cycle time test results at low and high idle engine speeds. The implement oil should be above 100F (38C) for accurate and repeatable tests. The average cycle times for low and high idle engine speeds are shown in Table 3. If these times significantly change further investigation and testing of the hydraulic system is warranted.
Table 3: Typical Cycles Times @ Low and High Idle Engine Speeds Lift Cylinder Position Average Cycle Time Engine Speed 2 – 70 deg 26-27 sec 750 RPM 2 – 70 deg 12 –13 sec 1656 RPM 10
Possible Reasons for Slower Cycle Times
1. Worn pump.
2. Leakage in the hydraulic system.
Relief Valve Settings
The main relief pressures for the lift and tilt head end cylinders are determined by moving the cylinders up against their stops and are recorded in Table 4. These results can be compared to previous tests to determine if there is a problem with the relief valve pressure settings.
Table 4: Main Relief Pressures for the lift
and tilt head end cylinders Lift Cylinder Pressure Tilt Cylinder Pressure 4425 psi 30510 Kpa 4030 psi 27786 Kpa
Possible Reasons for Changes in Relief Pressures:
1. Incorrect adjustment. 2. Failed relief valve.
3. Worn pump.
Test 4 & 5: Converter Stall Test & Double Stall Test
Engine ResponseThe engine response is measured during both stall tests. In the converter stall test, the service brake is applied followed by shifting the transmission into the highest gear available. Next, the engine speed is quickly accelerated from low to maximum speed. In the double stall test, the engine speed is accelerated before loading with the transmission and implements. If the load from the implements and transmission occur before increasing the engine speed, the engine would stall. The engine
response is respectively shown in Figures 6 and 7 for the converter and double stall tests and recorded in Table 5. The engine response time is measured from the initial throttle input to the time the engine reaches stall speed. The response time accuracy is to the nearest second since the data is collected at a one Hertz (once per second) sample rate.
The engine response time for the double stall cannot be obtained because the engine speed input occurred before the transmission and implements were stalled. The converter and double stall speeds for this machine are also shown in Figures 6 and 7 and recorded in Table 5.
The turbo outlet absolute pressure and torque converter temperatures are shown for each test in Figures 8 and 9.
Atmospheric pressure is plotted with the turbo pressure to calculate boost pressure. Boost pressure equals turbo outlet – atmospheric pressure. The boost pressure is also recorded in Table 5.
The engine response time, stall speeds and boost pressure should not significantly change over the engine life. If these parameters do significantly change, further investigation and testing of the engine,
transmission, torque converter, and hydraulic systems are warranted.
Table 5: Typical Steady State Values During Converter Stall and Double Stall Tests
Engine Speed Boost Pressure Response Time (min-
max engine speed)
Converter Stall 1520 + 25 RPM 16 + 1 psi 7 + 1 sec
Double Stall 1150 + 25 RPM 12 + 1 psi N/A
Possible Causes for changes in engine response, stall speeds and boost pressure
1. Leak in exhaust system. 2. Leak in air inlet system. 3. Failed fuel injector(s). 4. Failed valve(s).
5. Restriction in air inlet and exhaust system. 6. Failed turbo pressure sensor.
Exhaust Temperature Split Exhaust temperature split is the difference between the right and left exhaust temperature taken at the same time. The exhaust temperature split data is only meaningful during full load conditions. The engine is under a full load for the converter and double stall tests. Figures 10 and 11 respectively show the exhaust temperature split during the converter and double stall tests.
There is normally some difference between the left and right exhaust temperatures. If the exhaust temperature split is greater than 50°C (90°F) or a step change in the exhaust temperature split occurs, this may indicate a problem.
Possible Causes for a High Exhaust Temperature Split
1. Failed fuel injector(s). 2. Leak or break in fuel line
between fuel manifold and cylinder head.
3. Wrong valve clearance. 4. Leak in air inlet system. 5. Leak in exhaust system. 6. Restriction in air inlet or
exhaust system.
7. Wrong fuel injector lash. 8. Incorrect fuel injection
timing calibration. 9. Bent or broken push rod. 10. Failed exhaust temperature
sensor(s).
Test 6: Impeller Clutch Pressure Test
Impeller Clutch Pressure vs. Left Pedal The left pedal controls the impellerclutch pressure. Based on the left pedal position, the transmission electronic control module activates the impeller clutch solenoid valve. The impeller clutch solenoid valve controls the oil flow to the impeller clutch. The left pedal acts as an on/off switch at approximately 40% pedal travel. When the pedal crosses this
threshold, the impeller clutch pressure is reduced which limits the torque being transmitted by the torque converter. In the last 60% of pedal travel, the service brakes are engaged. This relationship can be verified by gradually depressing the torque converter pedal through its entire travel. A typical run at high idle is shown in Figure 12, and the results are recorded in Table 6. The table shows the relationship between left pedal position and impeller clutch
pressure at an engine speed of 1675 RPM. The initial impeller clutch pressure could have several varying values depending on the Reduced Rimpull Setting. Therefore, it is important to set the reduced/max rimpull enable switch to the MAX position. If the pressure levels significantly change, further investigation and testing of the system is warranted.
Table 6: Typical Steady State Impeller Clutch Pressures versus Pedal Position @ 1675 RPM
Left Pedal 0 % 41% 42% 85%
Impeller Clutch Pressure 259 psi
1786 Kpa 259 psi 1786 Kpa 72 psi 496 Kpa 72 psi 496 Kpa 14
Impeller Clutch Pressure vs. Engine Speed To improve engine and machine
response during engine acceleration, the impeller clutch pressure at low engine speeds is reduced. Figure 13 shows a typical run for impeller clutch pressure when engine speed increases from low to high idle. Table 7 shows the steady state relationship between engine speed and impeller clutch pressure. The impeller clutch pressure ramps from minimum to maximum between engine speeds of 950 – 1100 RPM. Since VIMS records data at a one Hertz sample (once per second) rate, the steady state relationship between 950 – 1100 RPM is difficult to capture. Therefore, it is critical to slowly ramp the engine speed to accurately record pressures during the 950 – 1100 RPM range. If this
relationship significantly changes, further investigation and testing of the system is warranted.
Table 7: Typical Steady State Impeller Clutch Pressures versus Engine Speed
Engine Speed 750 RPM 950 RPM 1050 RPM 1080 RPM 1673 RPM
Impeller Clutch Pressure 110 psi
758 Kpa 110 psi 758 Kpa 215 psi 1482 Kpa 251 psi 1730 Kpa 251 psi 1730 Kpa
Possible Reasons for Impeller Clutch Pressure Changes:
1. Damage to internal torque converter seal rings 2. Damage to impeller clutch piston seals. 3. Worn pump.
4. Failed impeller clutch solenoid or impeller solenoid valve. 5. Calibration is needed.
SELD7027 ©2006 Caterpillar Inc. Printed in U.S.A. (4/08)
Bulletin No. 6-1 (5/06) File Under Appendix