* 12-valve Cummins: The lift pump (the pump that moves fuel from the tank to the injection pump) is usually mounted on the engine block, near the fuel filter housing. The injection pump itself is also considered a fuel pump, and it's integrated into the engine, not a separate, easily accessible unit.
* 24-valve Cummins: Similar to the 12-valve, the lift pump is typically mounted on the engine block near the fuel filter. The injection pump is again integrated into the engine.
In both cases, you'll likely find it easier to access the lift pump by working from the top of the engine and potentially removing some parts (like the air filter housing or other components in the way) to gain better visibility and access. A service manual specific to your truck's engine (12-valve or 24-valve) will provide detailed diagrams and instructions. It is generally not recommended to try and repair it without a service manual.
Remember that working on a diesel fuel system requires care to prevent introducing air and potentially damaging the injection system. If you're not comfortable working on this yourself, it's best to consult a qualified mechanic.
