Cummins QSB Parts
Pick Engine to Find Parts
Select Your Model To Find Parts +
We have Cummins QSB parts for sale, in stock and ready to be delivered. These engines are generally used in non-highway uses, such as in marine engines, on construction sites or in industrial settings. We have many parts for these larger engines, plus we ship all orders within one business day, so you can get your parts quickly. We have arranged our site by engine type and series, so you can select the parts you need easily, all without the use of part numbers. If you have any questions or need help with placing an order, call us and we would be happy to help.
If you do not know which size engine you have, locate the dataplate. This will give you the series (QSB) followed by the displacement. If the dataplate can not be read, then check the top of the engine on the oil cooler.
For Cummins QSB troubleshooting, use the information below as a general guide.
Momentarily high oil pressure
Oil pressure in the Cummins QSB can vary based on the environmental temperature that the engine is operated in. To determine if it is, use the following specifications.
• The maximum oil pressure is 65 psi when under normal conditions.
• When it is cold, the normal oil pressure is 100 to 120 psi, and should drop to under 65 as the engine warms.
Consistent low oil pressure
Low, or no, oil pressure can be caused by the following situations. Be sure to also check the gauge, and use a manual gauge to confirm.
• High oil level, high enough to reach connecting rods. The oil may be aerated and should be replaced.
• Check the filter, which can cause a loss of oil pressure of about 10 psi. Replace the filter immediately if it shows signs of being clogged.
Low oil pressure during starting, followed by normal oil pressure
• On the bottom of the engine, check the oil suction tube to make sure it is not cracked, has a damaged gasket, or is loose.
Steady decrease in oil pressure over weeks or months
• This can be caused by a worn oil pump or bearings.
Sudden, large drop in oil pressure
• Check the expansion plug, which can blow and cause a large amount of oil to spill from the engine.
Oil is thin and black
Thin oil in a Cummins QSB can be caused by the following:
• This is usually caused by fuel in the oil.
• Check the fuel injection pump. The shaft seal may be bad.
• This can also be caused by incomplete combustion. Check the piston rings and injectors to make sure they are not leaking. An injector that is bad will cause the exhaust to be white when the engine is first started (for example, only in the morning.) Be sure to also check the injector's o-rings.
Oil is a milky color:
• This is usually caused by coolant in the oil.
• Check the expansion plugs, oil cooler element, cylinder head gasket and the engine block itself for leaks, cracks, or other signs of damage.
• Another way to check is to pressurize the cooling system to 20 psi and then remove the rocker lever cover to check for leaks, if they are here, then the cylinder head is cracked. The oil drain plug should also be inspected, and a leak here can indicated a bad cylinder head gasket, cracked cylinder head or block.
Intermittent loss of power when turning or going up a steep hill
• This can be caused by low oil level. Usually from the suction tube not being able to circulate the oil.
White smoke seen only when the engine if first stated (such as in the morning)
• This is usually caused by a leaking injector. Check the injectors and replace the injectors themselves as well as the o-rings.
Oil in coolant system
• Check the oil cooler element for any ruptures or leaks.
Oil seen in crossover tube
• Check the turbocharger for damaged seals.
Oil in breather tube
• Check the piston rings to make sure they form a seal.
Excessive Smoke and low power
• Check the internal components of the turbocharger. Specifically the bearing can cause friction.
Turbocharger, Oil seen past seal rings
If you have found oil past the seal rings in your Cummins QSB then check the following:
• Check the oil drain line, to make sure it is not restricted. • A damaged or restricted oil return line. • Intake or exhaust can be blocked. The charge air cooler should be flushed to clean oil from the system.
Turbocharger is making excessive noise
• Leaks in the air intake or exhaust. Check all of the hose clamps.
• Rattling can be due to foreign material in the inlet.
Rattling or clatter noise from engine
• Check the turbocharger to see if the inlet has any foreign objects.
• A clattering noise can occur if all of the main bearings are loose.
Loud knocking sound coming from engine
In the Cummins QSB, a loud knocking sound can be caused by different situations. Use the following as a guide. • If while pulling a load, check the main bearing to make sure it is not loose.
• Check the oil levels, as this can be caused by thin oil, or oil not reaching the main bearing.
• If it is more intermittent, and it occurs during idle as well as with a load, it can be due to worn crankshaft thrust bearings.
• If it is a double knock, seen during idle, then it can be due to a loose piston pin.
Diagnosing Engine Noise
• Start by disconnecting accessory drive belts to make sure the noise is coming from the engine.
• A loud knocking sound can be caused by a loose main bearing.
Air pressure rises slowly
This can be caused by several conditions in the Cummins QSB engine, check the following in order. • Check the air cleaner to make sure it is not clogged.
• Check the air compressor gaskets and hoses.
• Check the air governor to make sure it is set correctly.
• Check for carbon buildup in the air discharge line.
• Inspect the air compressor intake and exhaust.
Alternator is not charging
• First, check that the belt is not loose.
• Check the electrical system for blown fuses or broken wires.
• Make sure battery cables are not loose or corroded.
• Check the alternator output to make sure the voltage regulator is not malfunctioning.
Coolant loss is seen outside of the engine
• Check the hoses, draincocks, expansion plugs, pipe plugs, radiator, compressor and cylinder block.
• Check the radiator pressure cap.
• Check the cooling system hoses to make sure they have not collapsed.
• If none of the above, the engine may be overheating. Check the thermostat and gauges to make sure they are functioning.
Engine is gradually overheating
To diagnose overheating in the Cummins QSB, perform the following steps. • Open the cold weather radiator cover.
• Coolant is leaking from the seals or hoses.
• Check and/or replace the thermostat.
• Check that the radiator cap is on correctly.
• Repair, replace the fan shroud and the fan drive belt.
• Check that the cooling system hose is not collapsed or leaking.
• Ensure that the oil level is not too high or low, or contaminated with fuel.
• Check the water pump is working correctly.
• Clean and inspect the radiator core.
• Check or replace the torque converter.
• Check for leaks around the cylinder head gasket.
Engine suddenly overheated
• Check the coolant level and for any leaks.
• Check for incorrect fault codes.
• Make sure the winterfront is not closed.
• Check that the fan drive is not broken.
• Check the thermostat
• Check the water pump and replace if necessary.
• Check the radiator fins to make sure they are not bent.
• Check the cooling system component, and fan drive.
• Check all of the vent lines to make sure they are not obstructed.
Coolant temperature is below normal
• First, check the sensor and replace if necessary.
• Check the thermostat and the coolant flow.
Coolant is found in the oil (oil appears milky)
• Check the oil cooler to make sure it is not malfunctioning.
• Next, check the air compressor cylinder head, including the gaskets.
• If the engine has an aftercooler, check it any leaks.
• Next, check the cylinder head and expansion plugs.
• Lastly, check the cylinder head to make sure it is not porous.
You suspect excessive blow-by
Blowby (combustion gases leak into the crankcase) can be checked in the Cummins QSB by checking the folowing • First, check the air compressor by disconnecting the inlet and outlet lines.
• Next, check the oil seal on the turbocharger for any signs of leaking.
• The cylinder head may be too worn to perform properly. Check the specifications.
• Lastly, check the piston rings for any wear or damage.
Engine is showing poor acceleration
• Check the fuel tank to make sure it has fuel, and that the fuel lines are not leaking.
• Next, check the fuel inlet to make sure it is not restricted.
• If none are restricted, check the fuel lift pump and its filter to mae sure it is able to work properly.
• Next, check that the fuel pump overflow is operational.
• Make sure the air cooler is not restricted or leaking.
• If the problem is not seen here, check the accelerator pedal for malfunctioning.
• Next check the fuel lines to make sure they do not contain air, or that the fuel itself is not aerated.
• Make sure there are not any bends in the fuel line that goes into the cylinder head.
• Next, looks for any leaks around the fuel connector for any damage.
• Check the injectors to see if a unit was malfunctioning.
• If the injectors appear fine, next, check the air intake and exhaust for air leaks or restrictions.
• Check the exhaust system and exhaust brake to make sure it is free of restrictions.
• Next, ensure that the turbocharger is the correct size for your engine and is not malfunctioning.
• Lastly, the fuel pump should be removed and tested.
Engine is difficult or won't start, with exhaust smoke
These two sections are for diagnosing a Cummins QSB engine that is not starting like it should. If no exhaust smoke is seen, go to next section. • First check the fuel grade and amount, to make sure the engine has a proper fuel supply.
• Next, check the vents on the fuel tank. Remove and clean.
• Check the battery, including the electrolyte levels and add distilled water if needed.
• If the ambient temperature is cold, then starting aid may be needed. If there is an engine block heater, make sure it is not malfunctioning.
• Next, check the engine speed sensor. Make sure it is not covered with debris.
• Check the other components, such as the vehicle brakes and transmission.
• The fuel filter may be clogged. Make sure it is clean and that the fuel lift pump is able to move fuel.
• Check all of the fuel lines for restrictions.
• Try bypassing the fuel heaters to make sure the fuel is not too warm.
• Next, check the fuel lines, filters and connections for leaks.
• Check the injectors to make sure they are not malfunctioning.
• If these are not showing any signs, check the air intake and exhaust to make sure they are not clogged or in need of repair.
Engine Won't Start, no exhaust smoke seen
• Check the ECM to make sure it is not 'locked up' by disconnecting the battery for 30 seconds and reattaching.
• If the engine still will not start, try replacing the ECM.
• Next, check the engine speed sensor or circuit. Remove any debris from the sensor.
• If the sensor seems fine, check the fuel injection pump's voltage supply. Check the circuit.
• Next, check the fuel filter to make sure it is not clogged or dirty.
• Check the fuel lift pump for any inlet restriction.
• Next, check the fuel drain for any kinks, and clean or replace.
• Check the oil to make sure it is not aerated. If it is, vent the air from the system.
• Make sure the fuel connector is not damaged, nicked, or leaking fuel.
• Remove the injectors and verify the sealing washer thickness. If they are fine, check the injectors for signs of malfunctioning.
• If the injectors appear fine, they may need to be properly timed.
• If no other signs are seen, then replace the fuel injector pump.
Excessive engine noise
Loud continuous noise can be due to the following issues and problems.
• Loose fan belt drive.
• Leaks in the air system.
• Air intake or exhaust piping comes in contact with the chassis.
• The lubricating oil is not at the right level, diluted, or has high pressure.
• The vibration damper is loose or damaged.
• Coolant is too hot.
• Worn engine mounts.
• Rocker levels, shafts, valves are worn.
• Injectors are malfunctioning.
• The flywheel has loose capscrews.
• The torque converter is loose.
• The piston rings are damaged.
Engine runs rough at idle
The following can cause the Cummins QSB to run rough when in idle.
• A cold engine.
• Low fuel levels.
• Improper fuel grade.
• Fuel tanks are plugged.
• ECM is not properly calibrated.
• The engine idle speed is too low.
• There is moisture in the wiring connectors.
• A plugged fuel filter.
• Malfunctioning fuel lift pump.
• Kinks or restrictions in the fuel inlet.
• Air in the fuel system.
• Overflow valve is malfunctioning on the fuel pump.
• A restricted fuel drain, fuel supply, or connector line.
• Improper injector sealing washer.
• Malfunctioning injector.
• Worn or improper engine mounts.
Engine runs rough or is experiencing misfires
This condition can be caused by the following conditions/problems:
• Engine is too cold and needs to warm.
• ECM is not working properly.
• Clogged fuel filter.
• Fuel system has air.
• Clogged or restricted fuel inlet or fuel drain line.
• Fuel pump valve is malfunctioning.
• Malfunctioning injector or fuel injector pump.
• Obstruction between fuel line and injectors.
• Improper fuel grade.
Engine either shuts off or dies when you decelerate
The following can cause the engine to shut off unexpectedly:
• Low fuel level.
• Idle or PTO shutdown features are activated.
• Malfunctioning keyswitch circuit.
• Malfunctioning fuel injection pump voltage supply.
• Interrupted electrical supply line leading into ECM.
• Fuel system has air.
• Malfunctioning fuel lift pump.
• Exhaust brake is not working correctly.
• Pump going to the fuel injection pump is not working.
• ECM damaged or not working.
Engine starts but does not keep running
If you are experiencing these problems, they can be caused by the following issues:
• Low fuel level.
• ECM or fuel injection pump do not have power (voltage.)
• In-range intake manifold pressure sensor is stuck.
• Keyswitch circuit does not work.
• PTO or idle shutdown features are activated.
• Wrong fuel grade.
• Leaks in fuel connections, fuel filters and fuel lines.
• Dirty of clogged fuel filter.
• Restricted fuel suction line.
• Fuel system has air and needs to be vented.
• Non-functional fuel injection pump.
Engine that does not crank
The following are symptoms or problems related to an engine that does not crank:
• Low battery voltage.
• Corrosion or breaks seen on circuit connections.
• Starting circuit has malfunctioning component.
• Bad starter solenoid (does not make a sound).
• Wrong gauge for battery cables.
• Bad starting motor.
• A damaged motor pinion or ring gear.
• Hydraulic lock in a cylinder.
Excessive vibration
This symptom can be the result of any of the following sections:
• Misfiring engine.
• Problem with fan hub, alternator, refrigerant compressor or other belt-driven accessories.
• Worn engine mounts.
• Loose, damaged fan.
• Misaligned flywheel housing.
• Flywheel capscrews are loose.
• Hydraulic pump and air compressor are malfunctioning.
• Damaged vibration damper.
Unable to shut off engine
This condition can be caused by the following conditions:
• High counts of electronic fault codes.
• Malfunctioning keyswitch circuit.
• Air intake ducts are leaking, causing fumes to enter the air intake.
• Oil seal on the turbocharger is leaking.
• ECM or fuel injection pump is not working.
Excessive lubricating oil consumption
This condition can be caused by any of the following conditions:
• Oil is not proper specification.
• Leaking capscrews, pipe plugs, fitting and/or gaskets.
• Oil being blown into the air system by the air compressor, usually seen as carbon buildup and lubricating oil in the air lines.
• Leaking oil cooler.
• Improperly seated piston rings, or rings that are worn or damaged.
• Leaking seal around the turbocharger.
High oil pressure
The following are possible culprits if your engine is experiencing high lubricating oil pressure.
• Coolant temperature is too low.
• Wrong type of oil.
• Oil pressure regulator assembly is not working.
Low oil pressure
The oil pressure can be caused by the following conditions:
• Engine has too much or too little oil.
• Oil is leaking from the engine.
• Oil filter is plugged.
• Coolant or fuel is in oil.
• Engine is at too sharp of an angle.
• Oil pressure regulator is not working.
• Oil cooler is plugged
• Oil suction line and transfer tube is loose or broken.
• Gaskets or o-rings are leaking around oil pan.
Oil temperature too hot
Excessive oil temperatures can be caused by any of the following:
• Coolant is too warm.
• Lubricant level is too high or too low.
• Oil cooler needs to be replaced.
Oil is found in coolant
If you find oil in the coolant, check these following areas:
• Look for leaks around the oil cooler.
• Check the cylinder head gaskets for leaking.
• Check the cylinder head itself for any leaks.
• Check the hydraulic oil cooler and torque converter.
• Look for leaks around the air compressor cylinder head.
Excessive black smoke
Excessive black smoke can be caused by the following areas or situations:
• An ECM that is not properly calibrated.
• The manifold pressure sensor.
• Air intake unable to pull in air.
• Air intake manifold heater starting aid being plugged.
• Leaks in the exhaust.
• Fuel drain line not working.
• Malfunctioning injector.
• Turbocharger oil seal leaks, or wheel clearance not proper.
• Injector sealing washer incorrect thickness.
• Fuel injector timing is off.
• Raw fuel in intake manifold.
• Fuel injection pump has bad pump-to-engine timing.
Excessive white smoke
If you are experiencing excessive white smoke coming from the engine, it could be caused by any of the following conditions:
• ECM is experiencing problems.
• Engine is too cold. Try using a block heater or starting aid.
• Coolant temperature sensor is not working properly.
• Intake manifold pressure sensor is malfunctioning.
• Injector is not working or does not have correct sealing washer thickness.
• Poor quality fuel.
• Plugged fuel filter.
• Leak in the exhaust system.
• Restrictions in air cooler or fuel drain lines.
• Fuel lift pump not working.
• Coolant is leaking into combustion chamber.
Turbocharger leaking oil or fuel
If you suspect this condition, check the following areas to find the problem:
• Lubricating oil lines.
• Remove the turbocharger oil drain line to check for obstructions.
• Clean the crankcase ventilation system.
• Check the intake and exhaust piping for problems.
• Turbocharger oil seal.
Parts for Cummins QSB Series
>Select Your Model To Find Parts +
We have Cummins QSB parts for sale, in stock and ready to be delivered. These engines are generally used in non-highway uses, such as in marine engines, on construction sites or in industrial settings. We have many parts for these larger engines, plus we ship all orders within one business day, so you can get your parts quickly. We have arranged our site by engine type and series, so you can select the parts you need easily, all without the use of part numbers. If you have any questions or need help with placing an order, call us and we would be happy to help.
If you do not know which size engine you have, locate the dataplate. This will give you the series (QSB) followed by the displacement. If the dataplate can not be read, then check the top of the engine on the oil cooler.
For Cummins QSB troubleshooting, use the information below as a general guide.
Momentarily high oil pressure
Oil pressure in the Cummins QSB can vary based on the environmental temperature that the engine is operated in. To determine if it is, use the following specifications.
• The maximum oil pressure is 65 psi when under normal conditions.
• When it is cold, the normal oil pressure is 100 to 120 psi, and should drop to under 65 as the engine warms.
Consistent low oil pressure
Low, or no, oil pressure can be caused by the following situations. Be sure to also check the gauge, and use a manual gauge to confirm.
• High oil level, high enough to reach connecting rods. The oil may be aerated and should be replaced.
• Check the filter, which can cause a loss of oil pressure of about 10 psi. Replace the filter immediately if it shows signs of being clogged.
Low oil pressure during starting, followed by normal oil pressure
• On the bottom of the engine, check the oil suction tube to make sure it is not cracked, has a damaged gasket, or is loose.
Steady decrease in oil pressure over weeks or months
• This can be caused by a worn oil pump or bearings.
Sudden, large drop in oil pressure
• Check the expansion plug, which can blow and cause a large amount of oil to spill from the engine.
Oil is thin and black
Thin oil in a Cummins QSB can be caused by the following:
• This is usually caused by fuel in the oil.
• Check the fuel injection pump. The shaft seal may be bad.
• This can also be caused by incomplete combustion. Check the piston rings and injectors to make sure they are not leaking. An injector that is bad will cause the exhaust to be white when the engine is first started (for example, only in the morning.) Be sure to also check the injector's o-rings.
Oil is a milky color:
• This is usually caused by coolant in the oil.
• Check the expansion plugs, oil cooler element, cylinder head gasket and the engine block itself for leaks, cracks, or other signs of damage.
• Another way to check is to pressurize the cooling system to 20 psi and then remove the rocker lever cover to check for leaks, if they are here, then the cylinder head is cracked. The oil drain plug should also be inspected, and a leak here can indicated a bad cylinder head gasket, cracked cylinder head or block.
Intermittent loss of power when turning or going up a steep hill
• This can be caused by low oil level. Usually from the suction tube not being able to circulate the oil.
White smoke seen only when the engine if first stated (such as in the morning)
• This is usually caused by a leaking injector. Check the injectors and replace the injectors themselves as well as the o-rings.
Oil in coolant system
• Check the oil cooler element for any ruptures or leaks.
Oil seen in crossover tube
• Check the turbocharger for damaged seals.
Oil in breather tube
• Check the piston rings to make sure they form a seal.
Excessive Smoke and low power
• Check the internal components of the turbocharger. Specifically the bearing can cause friction.
Turbocharger, Oil seen past seal rings
If you have found oil past the seal rings in your Cummins QSB then check the following:
• Check the oil drain line, to make sure it is not restricted. • A damaged or restricted oil return line. • Intake or exhaust can be blocked. The charge air cooler should be flushed to clean oil from the system.
Turbocharger is making excessive noise
• Leaks in the air intake or exhaust. Check all of the hose clamps.
• Rattling can be due to foreign material in the inlet.
Rattling or clatter noise from engine
• Check the turbocharger to see if the inlet has any foreign objects.
• A clattering noise can occur if all of the main bearings are loose.
Loud knocking sound coming from engine
In the Cummins QSB, a loud knocking sound can be caused by different situations. Use the following as a guide. • If while pulling a load, check the main bearing to make sure it is not loose.
• Check the oil levels, as this can be caused by thin oil, or oil not reaching the main bearing.
• If it is more intermittent, and it occurs during idle as well as with a load, it can be due to worn crankshaft thrust bearings.
• If it is a double knock, seen during idle, then it can be due to a loose piston pin.
Diagnosing Engine Noise
• Start by disconnecting accessory drive belts to make sure the noise is coming from the engine.
• A loud knocking sound can be caused by a loose main bearing.
Air pressure rises slowly
This can be caused by several conditions in the Cummins QSB engine, check the following in order. • Check the air cleaner to make sure it is not clogged.
• Check the air compressor gaskets and hoses.
• Check the air governor to make sure it is set correctly.
• Check for carbon buildup in the air discharge line.
• Inspect the air compressor intake and exhaust.
Alternator is not charging
• First, check that the belt is not loose.
• Check the electrical system for blown fuses or broken wires.
• Make sure battery cables are not loose or corroded.
• Check the alternator output to make sure the voltage regulator is not malfunctioning.
Coolant loss is seen outside of the engine
• Check the hoses, draincocks, expansion plugs, pipe plugs, radiator, compressor and cylinder block.
• Check the radiator pressure cap.
• Check the cooling system hoses to make sure they have not collapsed.
• If none of the above, the engine may be overheating. Check the thermostat and gauges to make sure they are functioning.
Engine is gradually overheating
To diagnose overheating in the Cummins QSB, perform the following steps. • Open the cold weather radiator cover.
• Coolant is leaking from the seals or hoses.
• Check and/or replace the thermostat.
• Check that the radiator cap is on correctly.
• Repair, replace the fan shroud and the fan drive belt.
• Check that the cooling system hose is not collapsed or leaking.
• Ensure that the oil level is not too high or low, or contaminated with fuel.
• Check the water pump is working correctly.
• Clean and inspect the radiator core.
• Check or replace the torque converter.
• Check for leaks around the cylinder head gasket.
Engine suddenly overheated
• Check the coolant level and for any leaks.
• Check for incorrect fault codes.
• Make sure the winterfront is not closed.
• Check that the fan drive is not broken.
• Check the thermostat
• Check the water pump and replace if necessary.
• Check the radiator fins to make sure they are not bent.
• Check the cooling system component, and fan drive.
• Check all of the vent lines to make sure they are not obstructed.
Coolant temperature is below normal
• First, check the sensor and replace if necessary.
• Check the thermostat and the coolant flow.
Coolant is found in the oil (oil appears milky)
• Check the oil cooler to make sure it is not malfunctioning.
• Next, check the air compressor cylinder head, including the gaskets.
• If the engine has an aftercooler, check it any leaks.
• Next, check the cylinder head and expansion plugs.
• Lastly, check the cylinder head to make sure it is not porous.
You suspect excessive blow-by
Blowby (combustion gases leak into the crankcase) can be checked in the Cummins QSB by checking the folowing • First, check the air compressor by disconnecting the inlet and outlet lines.
• Next, check the oil seal on the turbocharger for any signs of leaking.
• The cylinder head may be too worn to perform properly. Check the specifications.
• Lastly, check the piston rings for any wear or damage.
Engine is showing poor acceleration
• Check the fuel tank to make sure it has fuel, and that the fuel lines are not leaking.
• Next, check the fuel inlet to make sure it is not restricted.
• If none are restricted, check the fuel lift pump and its filter to mae sure it is able to work properly.
• Next, check that the fuel pump overflow is operational.
• Make sure the air cooler is not restricted or leaking.
• If the problem is not seen here, check the accelerator pedal for malfunctioning.
• Next check the fuel lines to make sure they do not contain air, or that the fuel itself is not aerated.
• Make sure there are not any bends in the fuel line that goes into the cylinder head.
• Next, looks for any leaks around the fuel connector for any damage.
• Check the injectors to see if a unit was malfunctioning.
• If the injectors appear fine, next, check the air intake and exhaust for air leaks or restrictions.
• Check the exhaust system and exhaust brake to make sure it is free of restrictions.
• Next, ensure that the turbocharger is the correct size for your engine and is not malfunctioning.
• Lastly, the fuel pump should be removed and tested.
Engine is difficult or won't start, with exhaust smoke
These two sections are for diagnosing a Cummins QSB engine that is not starting like it should. If no exhaust smoke is seen, go to next section. • First check the fuel grade and amount, to make sure the engine has a proper fuel supply.
• Next, check the vents on the fuel tank. Remove and clean.
• Check the battery, including the electrolyte levels and add distilled water if needed.
• If the ambient temperature is cold, then starting aid may be needed. If there is an engine block heater, make sure it is not malfunctioning.
• Next, check the engine speed sensor. Make sure it is not covered with debris.
• Check the other components, such as the vehicle brakes and transmission.
• The fuel filter may be clogged. Make sure it is clean and that the fuel lift pump is able to move fuel.
• Check all of the fuel lines for restrictions.
• Try bypassing the fuel heaters to make sure the fuel is not too warm.
• Next, check the fuel lines, filters and connections for leaks.
• Check the injectors to make sure they are not malfunctioning.
• If these are not showing any signs, check the air intake and exhaust to make sure they are not clogged or in need of repair.
Engine Won't Start, no exhaust smoke seen
• Check the ECM to make sure it is not 'locked up' by disconnecting the battery for 30 seconds and reattaching.
• If the engine still will not start, try replacing the ECM.
• Next, check the engine speed sensor or circuit. Remove any debris from the sensor.
• If the sensor seems fine, check the fuel injection pump's voltage supply. Check the circuit.
• Next, check the fuel filter to make sure it is not clogged or dirty.
• Check the fuel lift pump for any inlet restriction.
• Next, check the fuel drain for any kinks, and clean or replace.
• Check the oil to make sure it is not aerated. If it is, vent the air from the system.
• Make sure the fuel connector is not damaged, nicked, or leaking fuel.
• Remove the injectors and verify the sealing washer thickness. If they are fine, check the injectors for signs of malfunctioning.
• If the injectors appear fine, they may need to be properly timed.
• If no other signs are seen, then replace the fuel injector pump.
Excessive engine noise
Loud continuous noise can be due to the following issues and problems.
• Loose fan belt drive.
• Leaks in the air system.
• Air intake or exhaust piping comes in contact with the chassis.
• The lubricating oil is not at the right level, diluted, or has high pressure.
• The vibration damper is loose or damaged.
• Coolant is too hot.
• Worn engine mounts.
• Rocker levels, shafts, valves are worn.
• Injectors are malfunctioning.
• The flywheel has loose capscrews.
• The torque converter is loose.
• The piston rings are damaged.
Engine runs rough at idle
The following can cause the Cummins QSB to run rough when in idle.
• A cold engine.
• Low fuel levels.
• Improper fuel grade.
• Fuel tanks are plugged.
• ECM is not properly calibrated.
• The engine idle speed is too low.
• There is moisture in the wiring connectors.
• A plugged fuel filter.
• Malfunctioning fuel lift pump.
• Kinks or restrictions in the fuel inlet.
• Air in the fuel system.
• Overflow valve is malfunctioning on the fuel pump.
• A restricted fuel drain, fuel supply, or connector line.
• Improper injector sealing washer.
• Malfunctioning injector.
• Worn or improper engine mounts.
Engine runs rough or is experiencing misfires
This condition can be caused by the following conditions/problems:
• Engine is too cold and needs to warm.
• ECM is not working properly.
• Clogged fuel filter.
• Fuel system has air.
• Clogged or restricted fuel inlet or fuel drain line.
• Fuel pump valve is malfunctioning.
• Malfunctioning injector or fuel injector pump.
• Obstruction between fuel line and injectors.
• Improper fuel grade.
Engine either shuts off or dies when you decelerate
The following can cause the engine to shut off unexpectedly:
• Low fuel level.
• Idle or PTO shutdown features are activated.
• Malfunctioning keyswitch circuit.
• Malfunctioning fuel injection pump voltage supply.
• Interrupted electrical supply line leading into ECM.
• Fuel system has air.
• Malfunctioning fuel lift pump.
• Exhaust brake is not working correctly.
• Pump going to the fuel injection pump is not working.
• ECM damaged or not working.
Engine starts but does not keep running
If you are experiencing these problems, they can be caused by the following issues:
• Low fuel level.
• ECM or fuel injection pump do not have power (voltage.)
• In-range intake manifold pressure sensor is stuck.
• Keyswitch circuit does not work.
• PTO or idle shutdown features are activated.
• Wrong fuel grade.
• Leaks in fuel connections, fuel filters and fuel lines.
• Dirty of clogged fuel filter.
• Restricted fuel suction line.
• Fuel system has air and needs to be vented.
• Non-functional fuel injection pump.
Engine that does not crank
The following are symptoms or problems related to an engine that does not crank:
• Low battery voltage.
• Corrosion or breaks seen on circuit connections.
• Starting circuit has malfunctioning component.
• Bad starter solenoid (does not make a sound).
• Wrong gauge for battery cables.
• Bad starting motor.
• A damaged motor pinion or ring gear.
• Hydraulic lock in a cylinder.
Excessive vibration
This symptom can be the result of any of the following sections:
• Misfiring engine.
• Problem with fan hub, alternator, refrigerant compressor or other belt-driven accessories.
• Worn engine mounts.
• Loose, damaged fan.
• Misaligned flywheel housing.
• Flywheel capscrews are loose.
• Hydraulic pump and air compressor are malfunctioning.
• Damaged vibration damper.
Unable to shut off engine
This condition can be caused by the following conditions:
• High counts of electronic fault codes.
• Malfunctioning keyswitch circuit.
• Air intake ducts are leaking, causing fumes to enter the air intake.
• Oil seal on the turbocharger is leaking.
• ECM or fuel injection pump is not working.
Excessive lubricating oil consumption
This condition can be caused by any of the following conditions:
• Oil is not proper specification.
• Leaking capscrews, pipe plugs, fitting and/or gaskets.
• Oil being blown into the air system by the air compressor, usually seen as carbon buildup and lubricating oil in the air lines.
• Leaking oil cooler.
• Improperly seated piston rings, or rings that are worn or damaged.
• Leaking seal around the turbocharger.
High oil pressure
The following are possible culprits if your engine is experiencing high lubricating oil pressure.
• Coolant temperature is too low.
• Wrong type of oil.
• Oil pressure regulator assembly is not working.
Low oil pressure
The oil pressure can be caused by the following conditions:
• Engine has too much or too little oil.
• Oil is leaking from the engine.
• Oil filter is plugged.
• Coolant or fuel is in oil.
• Engine is at too sharp of an angle.
• Oil pressure regulator is not working.
• Oil cooler is plugged
• Oil suction line and transfer tube is loose or broken.
• Gaskets or o-rings are leaking around oil pan.
Oil temperature too hot
Excessive oil temperatures can be caused by any of the following:
• Coolant is too warm.
• Lubricant level is too high or too low.
• Oil cooler needs to be replaced.
Oil is found in coolant
If you find oil in the coolant, check these following areas:
• Look for leaks around the oil cooler.
• Check the cylinder head gaskets for leaking.
• Check the cylinder head itself for any leaks.
• Check the hydraulic oil cooler and torque converter.
• Look for leaks around the air compressor cylinder head.
Excessive black smoke
Excessive black smoke can be caused by the following areas or situations:
• An ECM that is not properly calibrated.
• The manifold pressure sensor.
• Air intake unable to pull in air.
• Air intake manifold heater starting aid being plugged.
• Leaks in the exhaust.
• Fuel drain line not working.
• Malfunctioning injector.
• Turbocharger oil seal leaks, or wheel clearance not proper.
• Injector sealing washer incorrect thickness.
• Fuel injector timing is off.
• Raw fuel in intake manifold.
• Fuel injection pump has bad pump-to-engine timing.
Excessive white smoke
If you are experiencing excessive white smoke coming from the engine, it could be caused by any of the following conditions:
• ECM is experiencing problems.
• Engine is too cold. Try using a block heater or starting aid.
• Coolant temperature sensor is not working properly.
• Intake manifold pressure sensor is malfunctioning.
• Injector is not working or does not have correct sealing washer thickness.
• Poor quality fuel.
• Plugged fuel filter.
• Leak in the exhaust system.
• Restrictions in air cooler or fuel drain lines.
• Fuel lift pump not working.
• Coolant is leaking into combustion chamber.
Turbocharger leaking oil or fuel
If you suspect this condition, check the following areas to find the problem:
• Lubricating oil lines.
• Remove the turbocharger oil drain line to check for obstructions.
• Clean the crankcase ventilation system.
• Check the intake and exhaust piping for problems.
• Turbocharger oil seal.