i have a 01 f150 with the 5.4 engine, it keeps throwing the code p304 for cylinder number 4 misfire, i replaced the plug, coil, and fuel injector and clear the code and it still keeps coming back any ideas on what to check next

 

check the wires all the way back for burn marks or cuts on both the coil pack and injector, also does it only happen after a rain, or all the time?

 

all the time doesnt matter the weather. seems to run fine while driving but when it sits idling it idles kind of rough especially if i dont drive it for a couple days then start it up. all wires in seem to be in good shape

 

did you replace the spark plug with a motorcraft one? also does it burn a little oil? pull the spark out and see if there is oil on it.

 

Also check compression..

 

replaced all plugs with motorcraft ones, spark plug is dry and did a compression test and has plenty of compression

 

No plug wires or coil packs on a 5.4.
The 304 code tells you the issue is on the secondary side of the COP.
The coil secondary, the boot or the area that sets over the plug or broken plug, is in trouble.
Or some outside issue with the injector or cylinder.
.
How is the 304 generated?
The PCM keeps track of the rotation time, every time, for every cylinder via the front crank sensor.
If rotation time gets too long as compared to the average of all good cylinders, the code is set no matter the reason.
This design can even account for average cylinder wear over the engine's life.
Misfires are recorded in software monitors accessed by looking at mode 6, test 53 data points for every cylinder, using a Scanner.
.
An out right electrical failure of the coil or it's driver or wiring feed is totally a different detection means not related to rotation timing and shows as a code P035x, a primary operational signature failure..
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Be sure your not jamming/ hanging the boot tip off the top of the plug and the boot is good with no splits or pin holes.
This is one reason for the use of the dielectric grease so the boot tip 'finds' the plug when you can't see what is happening except by feel while setting the coil in place.
Good luck.

 

The boot on the coil is fine its brand new along with coil, plug and injector and i used plenty of dialetric grease when i put it in

 

You may have used too much grease, you don't want it on the spring where it contacts the plug.

 

I used the same amount of grease on the number 4 cylinder that i did on the other cylinders when i replaced the plugs and number 4 is the only one throwing a code

 

If you have done the plug coil boot and all compression test is good next swap injector 4 with #1 and see if the missfire moves.

 

Replaced the number 4 injector and code still comes back

 

Check the wiring harness where it passes by the A/C accumulator. Even if it's not chafed, the harness shouldn't be laying on the accumulator.

 

Harness is in good shape and not touching accumulator. Added a bottle of seafoam to my gas tank and been drivin the truck seems to run smoother but code still comes back

 

techron is the only proven fuel system cleaner. Seafoam=garbage.