I have 2006 F-150 4x4 with the 5.4 V8

It has high miles (208k) but has had all the coil packs, plugs, and fuel filter changed and the truck has run fine for a while.

It starts fine and idles well.
With the OBD reader on it, I won't see the cylinder misfire count increase.

Once you start to accelerate it starts bucking like it won't shift, and it certainly feels like it is misfiring....the check engine light will (sometimes) start to fash if you try to give it too much gas, but the misfires start to increase quickly.

The codes are always the multiple misfires, and it is usually cylinders 5,6, and 8......but don't quote me on that.

I have tested almost all of the coil packs (definitely already tested 5,6 and 8) and the coil packs read the correct resistance (.9) and I hooked a plug tester in between and grounded it to the block and the light pulsed with the spark.

The plugs also looked good....

I just recently changed the fuel filter as well....

Any thoughts....from all the reading I have done does anyone think it could be the cat?

 

No, I don’t think it is the cat.

How about the plug boots? Have they been changed?

 

No, but pulled them off when i was testing the coil packs. They looked good, but I’ll check again. Bad would be cracked or tears in the rubber?

 

Or pin holes or carbon tracks from arching.

 

So does anyone here think the boots are bad?

Going to change them all and all the plugs as well.

 

is the photo bad, or does the #3 plug have a HOLE in the side of it ???

 

I think its just the photo...does that look like carbon arcing due to bad boots?

 

Yup! Those black lines on the upper porcelain is carbon tracks. Which are your misfires. Replace your boots use a di-electric grease on the insides of them and either replace your plugs or clean all of the tracks off. If it where my truck I would just replace them, seeing as you already have them out.

 

Any idea what the torque specs are off the top of your head (ill search if needed)
Also, should I put anything on the threads and shaft of the plug?
Suggestions on plugs....

 

I had the same trouble with mine king ranch 2007 and had the clogged cat on that side,
all your misfire occurs on the same bank.
You dont miss anything for check that

 

Unfortunately I’m not at work, and can’t look up the torque spec. Ford has stated in a TSB to put high temp anti seize on the shaft of the plug, but as a professional who has been in the same facility for 12 years, servicing the same vehicles, I do not use any anti seize on any part of of the spark plugs for these engines, and I recommend you change your plugs every 50-80k and keep current on “induction services”. It helps clean and reduce carbon build up which is the enemy for our spark plugs. Also changing your plugs this regularly you protect your ignition coils from being over stressed. Which will cause early failure of ignition coils.

 

As a 5.4l owner / driver who has completely eliminated misfire problems (after much aggravation), I agree completely with everything @dysdow has said. In addition, as part of each 50-80k plug change, I use a solvent soaked rag on a piece of wire and clean the carbon out of the extended plug hole below the threads. This avoids carbon buildup ever touching the plug snout. I believe anti-seize (or ANYTHING) touching the plug tip negatively alters the designed intent of the special plug (altering its operating temperature - as well as leading to them seizing in the head).

 

So i put in all new plugs and boots and now I no longer get any misfire codes at all.

The truck still runs like it is missing, badly. Cant get over 3k RPM and over like about 40mph.

While driving I watched and no misfires at all.

After a while it finally threw a code, it was: P0171: System Too Lean Bank 1.

Any thoughts? It seems to idle fine as well

 

Check your freeze frame data. If the code is setting under load while driving i have a couple of checks for you. So logistically you can have a plugged cat on bank 2, or a disconnected IMRC linkage on bank 2 that will cause that code. Use a light and mirror to inspect the linkage on the back of the intake manifold, if that all checks out okay you may have a plugged cat. You would need to do a back pressure test.

 

How would I do a back pressure test? Is there a way to disconnect the cats?

Still no misfire's...I also checked the fuel pump, that showed 39psi at the fuel rails....