I don't have a manual handy to check for this so,I'll ask. On an 04 mustang gt 4.6 2v with the returnless style fuel system, there is a little,round,shinny metal diaphram looking thing inline just before the fuel line attaches to the rail. There are no vacuum lines or electrical connectors. Is this a fuel filter, some type or fuel pressure controller/limiter? or is this something to keep the fuel from running backwards??