I have a 4.6l f150 and Friday afternoon it started running real rough on the way home from work. I did a little research on the forum and decided to check the cops. I ohmed them all out and they all seemed to be good. They did not read 5500 ohms but more like 5000 ohms on the secondary. For the primary side the all measured around .6 to .8 so I figured they were all good. I also started the engine and removed 1 at a time and thought there might be a problem with one of them so I replaced it. Still no good. I also changed the fuel filter. After this the truck was nice and peppy and when getting on it , it got up and went and no rough running. Problem solved.....NOT. I got up today and drove itn to work and it is now still running rough. Can this be a fuel delivery problem? Need some advice... The CEL is not on but will go to Autozone today to see if they can get any codes off it....

 

How many miles on what brand spark plugs?

 

Well I just replaced the motor last summer with a rebuilt one from Ford. New plugs installed last year at that time. The engine now has 5000 miles on it.

 

When you did the swap did you clean your throttle body while it was off? Assuming you purchased a long block and had to use your egr, intake and throttle body, cop's etc... If they are original cop's, they could be in question.
So even though the motor is new, the ignition components are not. You may have also gotten some bad gas.....
Drive around and try to get it to misfire as much as possible and keep your eyes open for a flashing check engine light or hopefully it comes on.

 

Went to autozone and they got codes for 7 and 8 misfire. So I swapped out the cops and the engine is still rough. So cylinder 7 and 8 are on the right side of the engine when standing in front of the truck and looking at the engine. They are the 2 cylinders closest to firewall?

 

did it just start? has it rained recently where you live? My 5.4 did the same thing and the reason for the rough running was because water got on top of the motor from water splashing. best thing to do is reset on board computer and let it run for a bit till it smooths out it works trust me i just replaced my 5.4 and was so mad when this happened

 

If the cylinders are misfiring all i can think of to do is focus on what would cause the misfire. From what I have read and not having personal experience with it myself since I have a 4.2 the v8s have been known to have an issue with these misfire problems. Of course most of these problems occur from coil packs going bad but I believe u checked those. (Sorry bit of a novice I am assuming ur referring to these with the cop acronym) I have also read that some v8s actually have an issue where the spark plug works its way out of the block some how. If its the computer i do know that some auto shops besides dealers are equipped with these Pegasus Machines that do more than ur standard code reader. They give more indepth information on what the computer is thinking and if a hardboot of the flash is necessary these machines can perform that operation, but im also warned that messing with the computer cuz it can really screw some things up. I hope im being helpful. Good luck

 

Yes

And do yourself a favor before you chase it through all the cylinders, pick up a 10 pack of global cop's and install them correctly... Eliminate any other bad cop's.

Also, might be due for an injector cleaning, but your misfires are pointing at cop failure. So change them all.

 

WHAT BRAND plugs? "New" is not a brand...........................

 

plugs are motorcraft