Fuel Rail Plug Pressure Relief Valve for GMC 6.6L Duramax LB7 2001-2004Fuel Rail Plug Pressure Relief Valve for GMC 6. 6L Duramax LB7 2001 2004 Feature: Replaces stock or a shimmed pressure relief valve. Helps eliminate low fuel rail pressure DTC Codes P1093 and P0087(low fuel rail pressure during power enrichment) that are caused by an insufficient pressure relief valve (PRV) spring pressure. This leads to the valve opening too early which causes excessive amounts of fuel to be returned to the tank. Helps maintain fuel