If ran low on fuel meant ran out of fuel, try the primer pump on the driver side of the injection pump. It'll either have a flat plastic button that you press repeatedly or a finger loop that you release by unscrewing then pull out-push in prepeatedly. Loosen the big bolt (17mm wrench?) that goes through the spin-on fuel filter ahead of the injection pump. You're primed when fuel leaks out of the fitting.

Check that the stop lever isn't stuck in the 'down' position. The lever should rest against an internal hard stop in the vertical position. If you can move the lever upwards with the key in the run position, there is likely a problem with the vacuum switch actuated by the key. Remove the vacuum hose connected to the injection pump to until you can sort it out but note that you will not be able to shut-off the engine from the cabin.

Could be tired glow plugs or a bad glow plug relay but the problem will be getting the engine to fire, not keeping it running... certainly not after a few seconds.

Sixto
... stay tuned