DPU on Amtrak Surfliner No. 1761 to San Luis Obispo? Actually, its a helper unit from San Luis Obispo that brought Amtrak No. 774, the southbound Surfliner, From San Luis Obispo to Los Angeles. Power problems with the Amtrak engine required the assist. No. 4918 is tied on behind NPCU 90230 and is DIT back to San Luis Obispo.