My 06 F-150 recently started to misfire, I had the coil packs and spark plugs replaced about 4000 miles ago. I also just replaced my fuel pump module less that 500 miles ago. What could be causing this problem? The misfires are happening in cylinders 4 and 8, so the two most far back ones. Fuel injectors, fuel pump, fuel filter, faulty coils or plugs?

 

If it's consistently #4 and #8, then it's highly unlikely it's your fuel filter. I would lean more towards the plugs or COPs. Almost sounds like maybe they weren't torqued down correctly, especially since it's the 2 back cylinders. I would start with the plugs first.

 

And as always asked, what brand COP's did you use for replacement? Lots of cheaper replacements out there that fail early.

 

I assume this mis-fire is on a 5.4L 3V ??? How many miles on the motor ?? what brand parts were used for the COP’s and plugs...did you replace boots and springs ?? any other required maintenance been performed ?? Fuel filter ... TB cleaning ?? MAF cleaning ?? do the CATS smell or glow red ?? any DTC’s or a flashing CEL ?

 

People never give enough information..

 

start with the simple stuff first.
1. check that the plugs are torqued properly
2. check that the coils are on tight
3. check that all connectors are fully snapped in

 

Myself included, sometimes we just forget. The OP is new, lets help him out.

 

I once received a Misfire code about 6 months after replacing the plugs & COPs.

Plugs & COPs were good, it was actually the Fuel Injector that was acting up.

 

I am new to the site but I am having the same issue as well. my #4 is misfiring. I have changed the plugs and the coil packs and it will run great for about 3 days then the misfire reappears. all I have to do is take the plug out and replace and we are back in business.

I used Motorcraft SP-515’s well.. motor craft on both the plugs and coil pack.

side note... and this is the kicker. i did have a plug rocket eject out of this port as well. broke the coil and everything. the plug had a "sleeve" on the threads. seems I am not the first person to have issue with #4... would love to hear any suggestions.. __________________________________________________ _______________________

2001 ford f-150 with the 5.4 v8
about 130,000 on the engine.

 

Sense you are new I will be kind...start your own thread if you have a problem... don't Hi-Jack somebody else's... you need to have #4 plug hole re-sleeved.