RichP9

07 5.4 120k miles...

Hey everyone, ive been chasing a misfire code for a while now and im running out of ideas, i currently have a misfire code for #1 that comes up usually when im getting up to speed at better than half pedal or trying to accelerate when im already at highway speeds. if i drive easy, i dont get any studders or codes, and everything is happy. it idles decent but not as smooth as i feel it should, heres what ive done so far

i started with a trans flush, cause the first few times it happened it didnt throw any codes or check engine lights, it was just a low rpm highway speed shudder. changed the fluid which was original since it had the bobber in the pan still. with no change.
few days of normal driving later and it happens again, this time throwing a number 1 and 8 misfire code. after doing my homework i decide to change all of the coils, i used bwd coils from advanced. overall performance improved and my number 8 misfire code went away. but not number 1.

So on that note i decided it i had to bite the bullet and bring it to ford for them to do the plugs, they found two plugs damaged, number 1 and 7, strangely enough. Both of the porcelains were loose in the steel body of the plug, and on number one part of the hoop was missing.

after they changed them it ran about 10X WORSE, they refused to be any help so i looked at it myself again and found that the plug into the number one coil was damaged. i replaced the pigtail to it, Now after all of that i am back to a misfire in number 1 when under a slight load. and a bit of a rough idle. it runs worse under 1500 rpms but as long as i keep a light pedal it runs pretty good.

i apologize for the lengthy post but any help would be greatly appreciated, thanks guys

Mod (Ret.)

When the COPS were replaced, were the boots and springs also done (replaced)?

techrep

iTrader: (1)

Swap COP's 1 and 2...see if the miss-fire follows..this way you can eliminate the COP...do the same with the plug and fuel injector.

RichP9

yes, the boot and spring were replaced with the coils. i already swapped the coils from one and two but nothing else yet, how likley is it to get a bad plug out of the box?

RichP9

ive been doing some more reading around here and looks like a few people had similar issues and it ended up being a clogged cat, would that do it and only ever throw the one misfire code?

techrep

iTrader: (1)

try the plug first...what brand plugs did you install ? a clogged cat would be the results of a long term mis-fire condition...raw fuel gets in to the cat and will eventually clog it.

RichP9

they are motorcraft plugs. i havent got to swapping it yet most likely this weekend. will i do any long term damage if i keep driving it like this? its runs fine as long as im easy on it

Aeromech

How old is your fuel filter? On my 5.4 I believe the #1 injector is at the end of the line concerning the flow of fuel through the fuel rails. You might also pull at minimum the #1 injector and bench check it. You can also pull all the injectors and have them rebuilt and flow checked.

I had a cylinder 1 misfire and after installing a new COP it came back. Turned out to be a bad spark plug. So now I have a spare COP.

RichP9

i changed the fuel filter this weekend with a new motorcraft one. the old one seemed to be the original. it wasnt totally clogged but it was difficult to blow through compaired to the new one. Again it was an improvement but not a cure. hopefully i will get a chance to pull out the injector and probably just put a new one in.. how would i bench test it?

techrep

iTrader: (1)

you can swap injectors also and see if your mis-fire follows.. this way your not just throwing parts at it and money in the can.