Engine Difficult to Start or will Not Start (Cummins QSB3.3)
QSB3.3 CM2150
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| Figure 1.1 - Hard Start |
#Symptom Tree
1). Starting procedure is not correct - Verify the correct starting procedure. Normal Starting Procedure:
→Do not depress the accelerator pedal or move the accelerator lever from the idle position while cranking the Engine. This can result in Engine overspeed and severe damage to the Engine.
→To prevent damage to the starting motor, do not engage the starting motor for more than 30 seconds. Wait 2 minutes between each attempt to start (electrical starting motors only).
→Engines equipped with air starting motors require a minimum of 480 kPa (70 psi).
→Disengage the driven unit, or if equipped, put the Transmission in neutral.
→With the accelerator pedal or lever in the idle position, turn the key switch to the ON position, and wait for the WAIT-TO-START lamp to go out, then turn the key to the START position.
→If the Engine does not start after three attempts, check the fuel supply system. Absence of blue or white exhaust smoke during cranking indicates no fuel is being delivered.
→When using jumper cables to start the Engine, make sure to connect the cables in parallel: Positive/+ to Positive/+ and Negative/- to Negative/-. When using an external electrical source to start the Engine, turn the disconnect switch to the OFF position. Remove the key before attaching the jumper cables.
2). Fuel level is low in the tank - Fill the supply tank.
3). Fuel grade is not correct for the application, or
the fuel quality is poor - Operate the Engine from a tank of high-quality
fuel.
4). Fuel shutoff is malfunctioning - Check for loose wires and verify that the fuel
shutoff valve is functioning.
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| Figure 1.2 - Fuel Pump (QSB3.3) |
5). Battery voltage is low - Check the Batteries and the unswitched Battery supply circuit.
6). Key switch circuit is malfunctioning - Check the vehicle, equipment, or vessel
key switch circuit.
7). Air in the fuel system - Check for air in the fuel system. Tighten or
replace the fuel connections, fuel lines, fuel
tank standpipe and fuel filters as necessary.
Vent air from the system.
8). Fuel filter is plugged - Measure the fuel pressure before and after the
fuel filter.
9). Fuel supply is not adequate - Check the flow through the filter to locate the
source of the restriction. Read More: Fuel System Cummins B3.3 and QSB3.3 - Electronic Engine.
10). Fuel Pump Overflow Valve is malfunctioning - Check for external leaks/ other damage or replace the return overflow valve.
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| Figure 1.3 - Fuel Return Overflow Valve (QSB3.3) |
12). Fuel drain backup - Verify the fuel return line is plumbed to the
bottom of the fuel tank.
→Fuel Flow Rate Commanded = 0.00 gph
13). Throttle linkage misadjusted or damaged - Adjust or repair the linkage.
#Data Monitor/Logger (Cummins Insite)
1). Key switch ON position.
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| Figure 1.4 - Fuel System (Key switch ON) |
→Fuel Pump Actuator Commanded Current = 0.00 mA
→Fuel Pump Actuator Duty Cycle = 0 percent
→Fuel Pump Actuator Measured Current = 0.00 mA
→Fuel Pump Actuator Position = Open
→Fuel Rail Pressure Commanded = 7252 Psi
→Fuel Rail Pressure Measured = 60 Psi
→Fuel Rail Pressure Sensor Signal Voltage = 0.51 Vdc
2). Hard Start. Refer to Graphical Display (Figure 1.1) above.
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| Figure 1.5 - Fuel System (Hard Start) |
→Fuel Flow Rate Commanded = 22.56 gph
→Fuel Pump Actuator Commanded Current = 875 mA
→Fuel Pump Actuator Duty Cycle = 16 percent
→Fuel Pump Actuator Measured Current = 875 mA
→Fuel Pump Actuator Position = Close
→Fuel Rail Pressure Commanded = 5241 Psi
→Fuel Rail Pressure Measured = 2416 Psi (min. pressure for Engine to run)
→Fuel Rail Pressure Sensor Signal Voltage = 0.86 Vdc
3). Engine Run.
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| Figure 1.6 - Fuel System (Engine Run) |
→Fuel Flow Rate Commanded = 2.02 gph
→Fuel Pump Actuator Commanded Current = 1375 mA
→Fuel Pump Actuator Duty Cycle = 18 percent
→Fuel Pump Actuator Measured Current = 1375 mA
→Fuel Pump Actuator Position = Close
→Fuel Rail Pressure Commanded = 7252 Psi
→Fuel Rail Pressure Measured = 7237 Psi
→Fuel Rail Pressure Sensor Signal Voltage = 1.62 Vdc
4). Normal Start.
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| Figure 1.7 - Normal Start |
Normal Starting Procedure (After Engine is running):
1). The Engine must have adequate oil pressure within 15 seconds after starting. If the WARNING lamp indicating low oil pressure has not gone out or there is no oil pressure indicated on a gauge within 15 seconds, shut off the Engine immediately to avoid Engine damage.
2). Idle the Engine 3 to 5 minutes before operating with a load.
3). After starting a cold Engine, increase the Engine speed (rpm) slowly to provide adequate lubrication to the bearings and to allow the oil pressure to stabilize.
4). Do not operate Engine at low idle for long periods with Engine Coolant Temperature below the minimum specification. This can result in the following:
→Fuel Dilution of the lubricating oil
→Carbon build up in the cylinder
→Cylinder head valve sticking
→Reduced performance
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