I have a 2004 4.6L F-150. Just changed plugs and now is throwing a P0406 code (EGR position system voltage too high). There was nothing wrong with it prior to me changing the plugs however, I did unbolt the metal pipe that goes from the exhaust manifold up to the EGR valve, but I put it back on and made sure it was tight. Could this be the problem? Do I need to replace the gasket in there that I unbolted or is it something more serious? Oh yeah, in case the user name isn't clear, I'm no mechanic. Any help would be greatly appreciated!

 

Did you mess with the 2 vacuum hoses that run into the egr pipe? might have replaced them backwards.

 

no, i didn't remove them. I just got a new gasket so I'm going to try to replace the old one and see if that solves the issue. It ran fine for about 50 miles of hwy driving 70-80mph, then the engine started to stutter real bad

 

well, replaced the gasket only to find that there wasn't one on there at all. now the CEL is on and the codes are P0307 and P0316. Any suggestions?

 

what plugs did you use? Those are missfire codes po307 is # 7 2nd one back on the drivers side. Check to see the coil is plugged in good.

 

i used autozone's brand. i'm gong to change the plug out and swap the coil with another one and see what happens.

 

Your going to get misfires with those plugs. Modular engines are very picky about plugs. Motorcraft only..

 

alright well looks like i'm doing another plug change. thanks for the info. i'm sure i'll be back on here soon.

 

changed the plugs and it runs like a top! thanks for the help!!