Short answer
The lift pump (fuel transfer pump) supplies fuel from the tank to the injection pump. On the 5.9 24-valve Cummins with the Bosch VP44 pump, specialist sources say low supply pressure is a known cause of hard starts, surging and power loss, and they warn that the VP44 relies on fuel supply. The only real way to know is a pressure test with a gauge.
Start with the easy checks
- Install a fuel pressure gauge on the supply side, following your service information or the gauge maker's instructions.
- Compare readings at idle and under load with the spec in your service information.
- Replace the fuel filter before blaming the pump.
Likely causes, most common first
- Weak lift pump
- Lower supply pressure, especially under load.
- Plugged filter or restriction
- Same symptoms as a weak pump.
- Air leaks on the suction side
- Air in the fuel.
These are common causes, not a diagnosis. The same symptom can have a different cause on your engine; codes, tests and your service information decide.
When to stop and see a diesel tech
- Supply pressure is low after a new filter.
- Injection pump codes or a no-start.
- Fuel leaks of any kind.
Questions
What fuel pressure should a 24-valve Cummins have?
Use the figure in your service information for your engine and model year. We do not publish a single number here because sources quote different figures for different setups.
Related symptoms
My diesel cranks but will not start. Where do I begin?
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Troubleshoot →Where this comes from
- Blue Chip Diesel: VP44 and lift pump information (PDF)
- Geno's Garage / TDR Buyer's Guide: Fuel transfer pump (PDF)
- Diesel Power Products: How to check lift pump pressure on a 24-valve Cummins
- Pure Diesel Power: Cummins fuel pressure test procedure
Last reviewed 2026-10-19. General information only: confirm with your service information and a qualified diesel technician.