I have a 2002 model with a 5.4 triton. My check engine light is being very inconsistent. It will come on and stay on for a month or two, then turn off for week, then repeat the whole process again. The truck is running fine, except for every once in a while when I fire it up it starts shuddering. The Check engine light code is saying one of the ignition coils is down, but I've checked them out and they are all fine (I had them all replaced just over 6 months ago). Any ideas on what is causing this issue/how to fix it?

 

Does it say which coil is not responding/misfiring? Did you spend the money for motocraft coils or get cheap ones from Ebay/amazon? What actual codes are you getting? Did you change the plugs when you changed the coils? Did you try moving the "bad" coil to another spot and see if the problem follows?

It's possible either the coil is bad, the plug is bad, there is a wiring issue, or possibly a PCM issue.

 

I Got real coils, not that cheap crap , and they have a lifetime warranty. I had the entire system replaced (spark plugs, coils, the boots, etc.), and I first thought it was a wiring issue, except for the shuddering. The PCM is something I hadn't considered; how do you propose I check that?

 

Having a lifetime warranty tells me you probably bought them from a parts house....

What brand are they?

 

What do fake coils look like ?

Anyway, your post is very vague as far as a ignition problem. This is what the DTC's are for, -to help narrow it down. So what are they ? How are checking coils ? There isn't a way to load test coils without stress test equipment (a Rotunda kit).

We need names and numbers at this point. Sounds like you have a miss below 1000 rpms.

 

If your only code is intermittent misfire on 1cyl

with a non-misfiring cyl:

swap coil
swap plug
swap injector

Which cyl? PCV air leakage from bad tube will can #4 since its closest to pcv inlet in manifold

If it dont move with swapping pieces

it could be a wire or pcm issue
or it could be a hg leak
check fuel pressure , filter, prob not unless last cyl on rail
clogged throttle body ports

compression test
bubbles in coolant
losing coolant
look in cyl when cold thru spark plug hole

bad valve would be consistent, but hg varies with temperatures. comes and goes. misfires have to exceed threshold on test to throw code.
what does mode 06 count say when dont have mil lamp?

as sherlock holmes said, once you eliminate what it aint, your left with the truth.

 

I'm glad MBB touched on a compression test. A dead or weak cylinder would do everything a bad coil would do under load.

OP--If you have a specific code, you need to address it by itself. The PCM is setting this code due to what a sensor is telling it. I doubt the PCM is bad.

List the codes you have set and let's see if we can narrow it down for you. We have a good group of guys on here that can address just about everything. Maybe not always by just one person, but as a group we are hard to beat. There is a lot of experience on this site in the GEN 10's.

 

Did I miss it, or did the OP not say anything about checking the fuel injector?