Guys, My 2003 F150 4.6 Supercrew with 102,000 miles has set off a Po301 code that is an intermitant misfire in cylinder #1. (This might be a little long). I have changed the plug , coil ,injector and run Techron thru the system and still have the same problem. What do I do next?? (Please don't tell me I have a bad head or head gasket). Thanks for any and all replies.. Mud

 

I don't see plug wires listed. Have you done those also?

 

No plug wires in 03, COPs.

Green.....Did you clear the codes and see if it resets?

There have been a couple of recent posts, mine included, where the follower and lash adjuster have actually come out position and end up in the valve cover. It is an easy fix, if this happens, with just a new follower and new lash adjuster. I bought an 03 KR, 5.4 with this problem. I fixed it in about 3 hours. The hardest part was the cover removal.

 

Guys, Forgot to include that after I drive the truck about 100 yards the miss is GONE. Very strange to me. But it runs good after that 100 yards.. ????? Mud

 

I can tell you that with my Hyundai experience that codes don't always disappear right away and can take a few running cycles to clear from memory. I'd live with it for a little while, then clear it and see.

 

My 98 F250 with 5.4 had code P0303 ....new coil . plug , put a noid light on injector to make sure it was flashing ( did for about 10 seconds ) this can also be checked with test without pulling harness off ( hot wire on one side and other wire fed by pcm ) .. Ford said if pcm is bad , it will shut down cylinder if not getting fuel ....long story it was pcm ...now with my 03 F150 4x4 Sport with 4.6 Romeo did exactly same ...u drive sometimes fine but other times it would take about 5 miles to clear up ....small head gasket leak without water mixing in with oil cuz it was leaking into cylinder but unfortunately before i broke it down oil pump just went out and i spin Rod Bearing