Hi all I have a 2000 F150 4.2 w/153k on it. It has run great and still is. the other day I changed the fuel filter and the following codes appeared. PO401 (low flow EGR) and P)306 (#6 misfire) I have not noted a misfire. Never had an engine code before with this truck. FF is installed correctly. I work on airplanes so can fix a lot of things but this one has me stumped. I have not cleaned the EGR valve yet but will this week. Already had the codes cleared once. I was thinking air in the injector line because I did not relieve the pressure as book stated. Just R&R filter. Any thought on cause. kind of strange right after changing the filter. Thanks.