I recently had another check engine light on my 2008 4.6 l. with 200,000 + miles come on. After checking it with my code reader, it showed a 4th cylinder misfire code. As I had replaced no. 1 and 3 coils with Denso replacements in the last couple of months also, I assumed it was the coil. I put a new Denso coil in, but the truck is still skipping and throwing the same code. Thinking that I may not have installed the coil properly, I have removed and reinstalled it several times, still with no change. It is possible that the new coil is bad, but could the misfire be caused by a bad plug, instead? I bought the truck used so I don't know if the plugs have ever been replaced.

 

Do yourself a favor and put a set of motorcraft plugs in it. The are probably original with a 1/4" gap thats killing the coils. Replace the coil boots while you're there.

 

Swap the suspect coil with different cylinder, if the misfire moves, the coil is the issue, if the misfire stays, investigate a spark plug, injector, or compression issue on that cylinder.

 

That's probably your problem.

I don't really know the logic behind changing the coil on the #1 & #3, then #4 cylinders. I can only assume that it's financial, and that you can only afford 1 coil at a time.

Are you changing the boots also? Or just buying a coil, and re-using the old boot.

Start fresh. Replace every COP, with a new unit AND new boot. Change all of your spark plugs.

A lot of people will tell you to only use the MotorCraft. I think that the Denso brand is fine. You could try others. Some users have used different brands of tune-up parts, and did not experience problems. I've tried other brands like NGK, Denso, MSD, AutoLite, E3.......and my cars & trucks have been okay.

Use new parts. Don't report back that "local salvage yard had a clean looking set, came off a Mustang with the 4.6L, and that didn't fix the problem". You do not want to pull tune-up parts off a junk yard engine.

 

It senses the boost on crank when that cyl is supposed to kick it . So that's where firing order comes in it can be the cly on each side of firing order . Not the physical one next to it .

Plugs must be good /boots deteriorate with oil, antifreeze ,heat and time it only takes a pinhole . Fighting this one hole at a time is ridiculous.You are going to cause all kinds of codes/damage if you don't do a proper tune up . Plus you can burn out cops and pcm outputs. Learn to do a hosp clean plug job every 60k ,. Clean all cops connectors ,make sure all connectors lock on .
Learn to clean/test injectors on you tube .Dont use remans and change in sets of 4 /8.
If you abuse this Truck it will pay you back .
Buy quality stuff this isn't a tricycle .

 

I bought my Navigator with 130K on it. Around 140K it started having issue starting in the cold weather. I took the plugs out to see if they were dirty and found they were the original plugs with 140K on them and the gap was close to twice what it should've been. Like you I assumed the original owner would've changed the plugs at 100K like you're supposed to, but he didn't.

 

I believe Denso is the OEM so I wouldn't hesitate to use Denso coils in my truck. I've heard of cheap coils cooking the PCM so stay away from really cheap (ebay) ones. Also, I've heard about Fake Motorcraft coils making rounds, I think Ford even issued a statement about them.

 

I switched coils with one that was working and restarted the truck after clearing the code. The Check engine light came on within minutes of starting the truck. I had purchased 8 Motorcraft plugs, so I removed the no.4 cylinder plug and installed a new one. This time when I started it, it ran much more smoothly, so I took it for a drive and everything ran well and o check engine light. The electrode on the used plug was in rough shape. I will replace the rest of the plugs this weekend. Thanks to all who responded to my post.