I have a 2000 Lariat 4.6L 4x4 f150 supercab and recently the 5th cylinder was misfiring then it stopped then again and then it stopped again and then it was misfiring again so after changin all the plugs i bough a new coil and then it ran fine for 2 days then it started to misfire agian so i went to autozone to see if by any chance it was a different cylinder. They told me it was the same cylinder, but i just put a brand new coil. I was wondering what else it could be or if anybody has had this problem after replacing the coil any help would be appreciated.

 

Try swapping the #5 coil with another cylinder and see which misfires then.

 

I Switched it with the number 1 cylinder and now both are misfiring. DO you think the new coil is bad and maybe the plug is bad on the orginal. Cuz i changed the plug a month ago when it first did it and just changed the coil last week.

 

"I changed the plug a month ago" Did you change all the plugs or just one? What kind of plugs did you use?

 

try swapping the coils around and if you do have a bad coil, make sure to use oem parts only on the coil and plugs. good luck

 

How old are your plug wires??? Have you inspected the "suspect" plugs yet? If so, what did they look like?

Also, I have experienced plug wires coming loose on my 4.6... probably from never getting seated properly in the first place.

I believe you are suppossed to put a little grease inside??? Maybe electrically conductive grease to boot... I am not sure on this...

Anyone???

 

JHL, the 5.4L and 1999 and later 4.6L models don't have plug wires. They use "coil-on-plug" setup which has a coil mounted directly on each spark plug (8 coils).

 

I used the search function and done a lot of reading about this common problem.
Seems that the center 4 cylinders are the most often mentioned for misfire.
The reasons range from plugs to boots to coils to leaky cooling line over some plugs plus a sensitivity to moisture and even valve cover oil leakage in to the well area.
One very interesting finding, by scope testing, was that some coils are actually increasing there voltage output to as high as 90,000 volts.
Once this happens, the hi voltage damages the insulations and the plugs ablity to keep the spark from jumping to ground.
This means both the plug and the coil has to be changed no matter how recent the plug was changed because the new plug has been affected.
I would assume that many chase this problem because of this type of failure, for a long time, before thay get to the point of breaking the combination and not realize what was actually the original fault.
The PCM diagnostic program that detects this apparently is very very good to the point of showing the factory COP assembly is only marginal in ability to keep the spark under control and the plug/wires/boots and coil has to be near perfect.
Now this is just my analysis of what I read, having not experienced it first hand but still very interested in all aspects of the engine control systems.
Add some too this if anyone feels the urge.

 

wait.............heres a mistake i made once. i replaced some plugs on the 5.4 well some of the injectors were unplugged for easy acess. well i had one that wasnt plugged in all the way when i was done. take a quick look at those injector plugs..

 

Thanks for the info, this web site is like having a tech rep in the garage with you. Last year I had the transmission rebuilt on my 99 expedition, and it seemed to be slipping again in overdrive, under low torque, but apparently it was bad spark plug wires or faulty plugs. Replace all 8 today (plugs & wires) no misfire and the power is back. The plugs were replaced 2 years ago. Put motorcraft originals in this time around.
Also bought a coil just in case, but as of now, I don't need it.
AGAIN THANKS FOR ALL THE INFO!

 

Hi.

Glad you fixed your problem!

Yep, this is just the best site for us F150 folks. Bluegrass, Max, Neal, Mike, JP, and a lot of others, are all very helpful, great folks, with a tremendous sense of humour thrown in as a bonus!

Bluegrass - hi again. I have a quick question for you. During your research on the coil overvoltage, was there a root cause found for this condition? I would suspect too large a spark gap; a gap in spec ( given the plug was reasonably healthy, would not allow a voltage that high before discharging.

An abnormal high impedance condition within the plug or boot , or coil itself may contribute. I agree though, that this is going to cause damage if allowed to continue.

Are there any aftermarket alternatives for the COP system that are more robust? I know Mike Troyer mentioned a while back about a distributor conversion for a COP motor, for those fed up with COP heat soak and other failures ;-))

Cheers!