Need some help... My 2001 f150 4.6l started running rough a few days ago, it started misfiring under load with no check engine light. So I drove it a few hours more and the cel finally came on. I pulled codes and it stated a misfire detected in cylinder #1. So I started with a new motorcraft sparkplug and bought a new coil on plug coilpack at autozone. The problem seemed to go away for a day and then it came back. But now it just intermittently misfires. sometimes it runs good and sometimes its doesn't, It won't throw a cel and I don't know what to do now. I don't thinks its an injector or fuel filter cause its intermittent any thoughts would be appreciated
Thanks

 

Poor gas? I know my dad's old 99 needed to run on 89 otherwise it would knock. Did you happen to replace the plug boot also? Could also be the replacement coil. Unless the brand is an established brand (and not Duralast), Autozone brand parts aren't the greatest out there.

 

yea its a cheap duralast, im thinking i should of just got a motorcraft, I tried seafoam and 93 octane didn't help. Its weird the problem comes and goes it hard to diagnose

 

Egr valve can start to fail and let to much exhaust gas back in causing problems. You may want to look there and clean the egr valve. You can also move the coil and see the mis fire moves with the coil.

 

hooked it to a ford scan tool and watched the power balance nothing was unusual. figures it wouldn't misfire when hooked to the machine. checked compression, thats all good, swaped the #1 injector with #2 with no luck, swaped coil packs and plugs, no luck, this problem is completely intermittent. it missed like crazy going to work this morning and ran great coming home. I will check into the EGR valve next

 

Had a similar problem on my F150 and it was the egr. It never threw a code ever for it.