Is there any fault pointing to the crank sensor ? I would start by replacing that first, otherwise it's just probably low compression due to worn camshaft lobes but that would manifest by loss of power and strange blowing noises in the intake when the lifters are worn trough. Take the rocker cover and inspect the narrow cam lobes which press on the hydro lifters. If worn then replace the immediately ! Don't be tempted to buy cheap cams in, had a customer bringing me a cam he sourced of ebay and it did not look right to me. It came with non branded lifters and Glyco cam bearings. I fitted it just to find it snap as soon as i turned the engine by hand ! The engine would turn half way then it would stop ? All markings were on and i even took the glow plugs off to ease turning the engine ! The cam just snapped in 2 pieces and one lifter was cracked ! New, genuine parts were fitted after and that cam went straight in the bin ! As with everything in life you get what you pay for !