I recently purchased a 2006 5.4ltr. I am having all kinds of misfire problems with it and not throwing a cel. I have replaced all cop and spark plugs. Checked throttle body to make sure it was clean. After replacing all the coils and plugs the truck ran good for 3 days now it's back to misfiring again. Any help would be greatly appreciated.

 

Mileage on vehicle? What brand parts did you use?

 

121k put orielys coils in it and motorcraft plugs

 

Can you better define your misfire problems? Bucking, shaking, idling erratically, etc? How often does it do it? Does it only do it under certain conditions? (Providing as much detail as possible will help in determining probable cause)

 

Shaking at idle and around 45-50mph if you slightly accelerate it feels like a misfire

 

Almost like a shimmy

 

Assuming plug change went without a hitch? Properly torqued, etc?
What brand COP did you get from O'reilly?
Also, were these symptoms here prior to plug/COP change? Or is it new.

 

They are brake best. Spark plug change went ok I broke 2 off in the head and bought the extractor got them out just fine. I had a shop do the number 8 cylinder because I didn't want to mess around with it in my driveway

 

Never heard of "Brake Best". BWD maybe?

 

Was it doing this prior to change?