1999 DODGE RAM 2500 5.9L DIESEL

It's unlikely to damage the injector pump but the pump will eventually burn itself out. The pump SHOULD turn off when it attains full pressure. If it does not do so, check for proper pressure at the fuel pressure regulator. If pressure is OK at the output but high at the input, replace the pump. If pressure is high on both sides, replace the fuel pressure regulator.

check fuel shut off selenoid at fuel pump
may be week when hot

I would look more at your injector pump than the lift pump....Dodge does have a problem with there fuel delivery ( not enough consistent PSI ) which in turn takes out the injector pump mainly because the pump has be running to lean...So look at replacing your delivery pump with something 14PSI or greater, unfortunately sounds as though you will have to get your injector pump either replaced or rebuilt

This usually happens when the lift pump gets worn and fuel pressure drops below 7lbs and the injection pump has to work harder by pulling in the fuel and will destroy the pump,your is probably a vp44 fuel injection pump it needs replaced and they are expensive 1200.00+ but also change the lift pump or change to a fass fuel system,if the lift pump went out and you replace the injection pump it will ruin it in a short time.
The injection pump is not an easy job to change or for a novice mechanic as it has to be set in time with the engine at top dead center,and then the whole fuel system needs to be bleed of air.

Please clarify the "loosing power" does it lose power and shut down or does it loose power but will idle? Your Cummins is electronically controlled so oil condition is important, fuel leaks, oil leaks, leaks in the air ducting between the turbo and the intake, sensors, water in the fuel. Do you get an engine light when this trouble happens? Dodge uses a lift pump to carry fuel to the the injection pump, is it working?

if idling rough sound like air in system.and your injection pump timing is off.

It is my understanding that the fuel lft pump has been replaced( updated) and is now gone back to the old way and is re installed in the tank.

I have had to put 3 lift pumps in since new, little did I know but Cummins tells me that the lift pump delivers minimal pressure and shortens the life of your injector pump.

So if that is true perhaps it is best to eliminate the lift pump and go with the new in tank pump. I plan on doing it the next time I have a problem.

When the key is turned to the start position, the pump should run for about 20 seconds. Do this 3 or 4 times to prime the pump.

If it still doesn't start, the bad lift pump may have damaged the injection pump. Crack a fuel line loose (don't remove it) and turn the engine over, you should have fuel at the fitting.