It should also be remembered that the vast majority of faults are caused by (for one or more reasons) lack of fuel in the injectors, so you should start by checking the presence of fuel in the tank. This is especially important for vehicles that can start on flat ground but then run on rough roads. Fuel leaks around the fuel tank may indicate the presence of leaks that can lead to air entering the fuel system and malfunctioning of the injection pump.
WARNING: Before replacing expensive parts, check for any possible faults associated with less expensive parts or systems.