I have a 2003 F150 5.4 and have been having some trouble with a misfire for some time.
It occurs in cylinder #5, and so far I have replaced the plug (all of them in fact) and the
injector. I have also swapped the plug HV pack with that from #4 and still get the #5
cylinder misfire together, at times, with a running lean error code.

Now that we are in the depths of winter, I have discovered that the problem only happens
on damp, dreary days. If all is sunny and fine then no problems!

It therefore, Dr. Watson, seems that my problem is moisture related. I have liberally sprayed
WD40 everywhere I could, but to no avail.

Apart from replacing the entire ignition cabling, which is obviously not something I wish to do,
can anyone point me to any likely places/connections that I should check out?

Thanks in advance.

Malcolm

 

I've had similar issues when it was damp or raining outside with a 2003 Ford Escape. I had tried new plugs, coils, CRC Wire dryer, WD 40, you name it. I ended up talking with some other Escape owners with similar issues online and had traced it back to ECM wiring issues where the harness connected to the module. Did some more research and found the newer model years with the same engine had been updated to an improved design wiring harness that had a more weather proof type of connection from the harness to the ECM itself. Unfortunately someone spun out on an icy road one morning on my way to work and hit me totaling the vehicle before I could get it 100% figured out. I'd suggest taking a look at the ECM wiring harness if you haven't already to see if there are any exposed connections like the Escapes had that year.

 

1. What brand of plugs did you use? Motorcraft only!!!
2. If you are having issues only when raining it could be a GEM issue and you might have a leak from your windshield.

There are some other potentials out there too

 

I used Motorcraft plugs. I also pulled #5 plug recently to check for fouling but it was OK.
I will try to trace the connections to the GEM and check them out.
Thanks for your reply.

 

I will concentrate on those connections when the weather clears up and I can get the beast in my garage. I have my pride & joy Jag XK-8 stored in there at present.

 

Explain a little better, define,- HV pack. There isn't such a thing AFAIK. Are you trying to come with 'coil' by chance ? I'm going to go with that for now, but yea, confirm that's what you mean.

Before you swapped coil #4 with coil #5, did you clear the KAM KeepAliveMemory ? Disconnect the battery for 15 minutes or more before restart ?

When and Where in the rpm range and/or drive cycle does the miss first appear. Include idle of above in park and miss under load in drive.

What's the code/dtc - PO305 ?

 

Yes- ignition coils.

I didn't clear the KAM. I did not see any reason to.

Misfire occurs at idle as well as under load, where it is obviously more noticeable.

And finally, yes it was/is code P0305.

I will be working on the PCM connections today, so will see if that makes any difference.

 

PCM connections ? Yea I don't see a reason to.

Perhaps coil signal, that's easy and it will rule out PCM. You test for signal at the coil connector with test light or noid while cranking the engine. If the test doesn't signal on /sig off (blink), then it's a harness or PCM issue.

Takes only a few minutes but rules out a lot. Also, while your verifying coil signal, verify injector signal in the same fashion. Check your VRef from the battery as well for both.

You tested the coil, the coil is good correct ? You said you did and it's important that you did. This is true correct ?

If everything is good up to this point, then something is up internally, - need to compression check the cylinder.

This type of thing doesn't happen much, it's usually a coil problem. You move on to compression testing after verifying the above as not the issue.

 

The problem was a cracked intake manifold. $1100 later and all is good again. For now.