Saturday, January 26th, 2013 AT 1:25 AM
I have F-250 with a 5.4 gas engine. It has the check engine light on witch says their is a misfire in both #1 and #8 cylinder. I changed the fuel filter, and also ran fuel injection cleaner on a long freeway drive. Also it was pinging, so I started using high octane gas, and this seemed to help. It seems as if the timing is advanced slightly to cause the ping. What test should I do first to diagnose the problem?