To begin repairing a diesel RV engine that won't start, you must first understand the potential causes of the problem. Diesel engines are notorious for having starting problems in cold weather, so if the temperature is low, engine oil thickens and battery output drops. Thicker oil adds resistance to the movement of internal moving parts when the engine is started. A low battery can diminish the engine's ability to crank fast enough.
To confirm if thickened engine oil is causing the problem, check the oil's viscosity via the engine dipstick. If the oil is syrupy, replace the engine oil. For best results, switch to a lighter oil such as 10W-30 or a CG-4 rated synthetic motor oil.
If the engine cranking speed is inadequate, check the condition and charge of the battery. If the battery is low, recharge it using a trickle charger.
If the diesel engine doesn't start regardless of the ambient temperature, low compression or inefficient fuel delivery could be the cause of the problem. Check the fuel filters and lines, and clear out any obstructions.
If there is no click inside the injection pump when the ignition is turned on, the problem may be in the solenoid and/or injection pump assembly. Repair or replacement of one or both assemblies may be necessary.
If a click can be heard in the injection pump but no fuel is coming through the injector lines, the pump must either be repaired or replaced.