A couple weeks ago I started getting a P0403 code. I replaced the EDIS coil packs, plug wires, and plugs. Still misfiring. I replaced the #3 fuel injector. Same problem. Checked for vacuum leaks and any physical damage on or around the cylinder. Everything else is fine. Since the misfire is not consistent (the engine will run smooth for about 10 seconds and start misfiring and off and on), could it be the fuel injector harness or wiring on that injector? If so, how could I check that? What else should I look for?

 

Hold on here.
A #3 cylinder miss is not a code P0403.
What am I missing?
You better look for an EGR fault!
Ignition work is not going to fix an EGR fault.

 

My bad. I must've wrote the code down wrong. The code reader clearly said #3 cylinder misfire. I had an EGR valve problem, but I already replaced that. That's probably where I got the code from.

 

Satan,
Same year, same great history, same miss. Same code (0303) same steps so far (plug, wires, coil, and cleaned injectors). Talked to a Ford dealer but that was hopless. When I was done I was sure I knew more than he did and I don't know jack! I have seen multiple threads here on the #3 going bad and no real solution. Why aren't the other 7 cylinders doing this? Computer?

 

Some cases can be quite involved. If your sure the work done has no flaws then it's time to get deeper in to the troubleshooting.
This begins to get out of the relm of the owner ability.
Compression check, vacuum gauge look to see what the vacuum is doing.
An ignition scope check etc.
The way the computer detects a cylinder that has a problem is quite involved.
The cam sensor is used as a basis to time the rotation of the crank indicating the power the cylinder adds to rotation. It must be within a time frame plus a little tolerence, that is matched against a table that is built in the computer's memory. This table is even modified over time to fit the average for the engine.
I'm just alerting you to how deep this all gets. Anything that causes detection outside the limits will trigger the code and if bad enough you will feel a miss.
Plugs, gas additive deposits, coil, wire, injector, water in the fuel, outside moisture, marginal detection, air leak at the peticular cylinder intake port etc.
You have about the whole picture here and some of it you can't deal with yourself. The dealers even have a hard time with the whole thing when they don't know enough about it and won't get deep enough into solving the faults.
One thing's for sure; if a dealer does take the time, you have to pay for that time even though it gets excessive for what the problem turns out to be.
Good luck.

 

Have a P0302 code come up on Saturday, misfired for about 20 minutes, then ok; SES light stayed on all weekend, without a miss. Started it today at noon, misfire all the way home & back, intermittent, worse under heavier throttle. Friend mechanic with scanner read code, #2 misfire. Changed plugs 2000 miles ago. Put dielectric compound on all plug terminals. I think maybe not enough dielectric lube. Pulled off that plug cap, quick visual inspection, frigged with it when putting it back on, to clean terminal. Also pulled #2 injector plug off of injector, check for corrosion, etc, ok. Put back on, cleared code, no miss. No code. Just before doing this, we could make it miss on demand with park brake on and a bit of throttle, was even misfiring when giving a good poke of fuel in Park.
My advice, clean (or replace) wires and terminals, put LOTS of dielectric lube in terminals and put some in every connection you can get it into. Will follow my own advice very, very soon.
Denis.