01-06-2026, 02:46 AM
A diesel engine that cranks but refuses to start can turn a productive workday into a long diagnostic challenge. The Case 680K loader‑backhoe, a machine known for its durability and long service life, is no exception. When fuel delivery issues, air intrusion, or mechanical wear appear, the engine may crank endlessly without firing. Understanding the common causes behind a no‑start condition helps owners and mechanics restore the machine to reliable operation.
Development History of the Case 680K
The Case 680 series has been a cornerstone of the construction industry since the 1960s. The 680K, introduced in the early 1980s, represented a major step forward with improved hydraulics, stronger loader arms, and a more efficient diesel engine. Case Construction Equipment, founded in 1842, had by then become one of the world’s leading manufacturers of loader‑backhoes, with global sales of the 680 series exceeding tens of thousands of units.
The 680K typically used a Case‑built diesel engine paired with a Roosa Master or Stanadyne rotary injection pump. These pumps were widely used across agricultural and construction machinery, making parts and service knowledge relatively accessible even decades later.
Terminology notes
Symptoms of the No‑Start Condition
The machine in question displayed several classic signs of fuel system trouble:
Why Sitting Idle Causes Fuel System Problems
Diesel fuel degrades over time, especially when exposed to moisture. When a machine sits unused for months or years:
The Role of the Injection Pump in the No‑Start Issue
The rotary injection pump used on the 680K relies on a precisely controlled metering valve. If this valve sticks in the closed position, the pump will receive fuel but will not deliver any to the injectors. This matches the observed symptoms: fuel at the inlet, nothing at the injector lines.
A weak or nonexistent return flow also indicates that the internal transfer pump is not circulating fuel properly.
Common causes include:
Testing the Fuel System
Several diagnostic steps help narrow down the problem:
Check fuel flow to the pump
If fuel reaches the pump inlet with good pressure, the lift pump is functioning.
Crack injector lines
If no fuel pulses appear while cranking, the injection pump is not delivering fuel.
Inspect the return line
A healthy pump produces a steady return flow. A weak dribble indicates internal failure.
Prime the system manually
If priming does not restore flow, internal components are likely stuck.
Check the shutoff solenoid
If equipped, ensure the solenoid retracts fully. A stuck solenoid can block fuel delivery.
Why Air Intrusion Matters
Air leaks in the fuel system can mimic pump failure. Even a pinhole in a suction line can prevent the pump from drawing fuel. However, in this case, fuel reached the pump consistently, making air intrusion less likely.
Terminology note
When the Injection Pump Requires Rebuild
If the pump receives fuel but does not deliver any, a rebuild is usually necessary. Rebuilding a rotary pump typically includes:
A small anecdote illustrates this: A contractor in Alberta revived a 680K that had sat for five years. The pump was completely varnished inside, and the metering valve was frozen solid. After a rebuild, the machine started instantly and returned to service for another decade.
Other Possible Causes of No‑Start
Although the injection pump is the most likely culprit, other issues can contribute:
Preventing Future Fuel System Failures
Several preventive measures help keep older diesel systems healthy:
Company Background and Industry Context
Case Construction Equipment, part of CNH Industrial, has been a major force in the loader‑backhoe market for decades. The 680 series helped Case dominate the North American backhoe market during the 1970s and 1980s. The company’s global distribution network and long‑term parts support have kept machines like the 680K working well into their fifth decade.
Conclusion
A Case 680K that cranks but will not start is almost always suffering from a fuel delivery failure inside the injection pump. When fuel reaches the pump but does not exit through the injector lines, the metering valve or internal transfer pump is likely stuck or worn. With a proper rebuild and fresh fuel, these engines typically return to reliable operation. The 680K remains a durable and respected machine, and with proper maintenance, it can continue serving job sites for many years.
Development History of the Case 680K
The Case 680 series has been a cornerstone of the construction industry since the 1960s. The 680K, introduced in the early 1980s, represented a major step forward with improved hydraulics, stronger loader arms, and a more efficient diesel engine. Case Construction Equipment, founded in 1842, had by then become one of the world’s leading manufacturers of loader‑backhoes, with global sales of the 680 series exceeding tens of thousands of units.
The 680K typically used a Case‑built diesel engine paired with a Roosa Master or Stanadyne rotary injection pump. These pumps were widely used across agricultural and construction machinery, making parts and service knowledge relatively accessible even decades later.
Terminology notes
- Injection pump meters and pressurizes fuel for delivery to each cylinder.
- Lift pump (or transfer pump) supplies low‑pressure fuel from the tank to the injection pump.
- Air intrusion refers to air entering the fuel system, preventing proper fuel delivery.
- Return line carries excess fuel back to the tank.
Symptoms of the No‑Start Condition
The machine in question displayed several classic signs of fuel system trouble:
- The engine cranked normally but would not fire.
- Fuel reached the injection pump inlet, but nothing emerged from the injector lines.
- The return line produced only a weak dribble of fuel.
- The machine had been sitting for a long period before the issue appeared.
Why Sitting Idle Causes Fuel System Problems
Diesel fuel degrades over time, especially when exposed to moisture. When a machine sits unused for months or years:
- Fuel thickens and forms varnish.
- Internal pump components become sticky.
- The metering valve may seize.
- The pump’s internal transfer pump may lose prime.
- Rubber seals dry out and crack.
The Role of the Injection Pump in the No‑Start Issue
The rotary injection pump used on the 680K relies on a precisely controlled metering valve. If this valve sticks in the closed position, the pump will receive fuel but will not deliver any to the injectors. This matches the observed symptoms: fuel at the inlet, nothing at the injector lines.
A weak or nonexistent return flow also indicates that the internal transfer pump is not circulating fuel properly.
Common causes include:
- Stuck metering valve
- Failed internal pump seals
- Broken pump drive shaft
- Worn transfer pump vanes
- Internal corrosion from stale fuel
Testing the Fuel System
Several diagnostic steps help narrow down the problem:
Check fuel flow to the pump
If fuel reaches the pump inlet with good pressure, the lift pump is functioning.
Crack injector lines
If no fuel pulses appear while cranking, the injection pump is not delivering fuel.
Inspect the return line
A healthy pump produces a steady return flow. A weak dribble indicates internal failure.
Prime the system manually
If priming does not restore flow, internal components are likely stuck.
Check the shutoff solenoid
If equipped, ensure the solenoid retracts fully. A stuck solenoid can block fuel delivery.
Why Air Intrusion Matters
Air leaks in the fuel system can mimic pump failure. Even a pinhole in a suction line can prevent the pump from drawing fuel. However, in this case, fuel reached the pump consistently, making air intrusion less likely.
Terminology note
- Suction leak refers to an air leak on the low‑pressure side of the fuel system, often invisible because it does not leak fuel outward.
When the Injection Pump Requires Rebuild
If the pump receives fuel but does not deliver any, a rebuild is usually necessary. Rebuilding a rotary pump typically includes:
- Replacing seals and gaskets
- Cleaning varnish and corrosion
- Replacing worn vanes
- Calibrating the metering valve
- Testing on a pump bench
A small anecdote illustrates this: A contractor in Alberta revived a 680K that had sat for five years. The pump was completely varnished inside, and the metering valve was frozen solid. After a rebuild, the machine started instantly and returned to service for another decade.
Other Possible Causes of No‑Start
Although the injection pump is the most likely culprit, other issues can contribute:
- Clogged fuel filters
- Collapsed fuel lines
- Blocked tank pickup
- Faulty lift pump
- Stuck injectors
- Low compression from worn rings or valves
Preventing Future Fuel System Failures
Several preventive measures help keep older diesel systems healthy:
- Use fresh diesel fuel and avoid long storage periods.
- Add fuel stabilizer when storing equipment.
- Replace filters annually.
- Drain water separators regularly.
- Run the machine at least once a month to circulate fuel.
- Keep the tank full to reduce condensation.
Company Background and Industry Context
Case Construction Equipment, part of CNH Industrial, has been a major force in the loader‑backhoe market for decades. The 680 series helped Case dominate the North American backhoe market during the 1970s and 1980s. The company’s global distribution network and long‑term parts support have kept machines like the 680K working well into their fifth decade.
Conclusion
A Case 680K that cranks but will not start is almost always suffering from a fuel delivery failure inside the injection pump. When fuel reaches the pump but does not exit through the injector lines, the metering valve or internal transfer pump is likely stuck or worn. With a proper rebuild and fresh fuel, these engines typically return to reliable operation. The 680K remains a durable and respected machine, and with proper maintenance, it can continue serving job sites for many years.
