Alright folks I'm new here and I'm at a loss I've been working on this truck for two years with no progress. I have a 2004 fx4 5.4 3v it all started when I changed plugs no biggie done it before, well when the truck was put back together it had a horrible misfire cylinder's 5,7,8 since then I have replaced coils twice, spark plugs twice, all four oxygen sensors,fuel injectors, and pcm to no avail. Cylinder 8 is still giving a p0358 code but I have constant 12v to that coil with a ground pulse signal and it still runs horrible. Any thoughts or ideas would be greatly appreciated.

 

For ***** and giggles...I'd check the fuel pressure at the rail.

 

What brand plugs are you using? If they are anything but Motorcraft, get them out. Also when/if you pull them, examine the ceramic insulators very closely for hairline cracks.
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I'd ck compression before any thing else was changed

 

Definitely check compression. When you changed plugs did they come out in one piece or did they have to be extracted after breaking? If they had to be extracted there is a possibility that debris fell into the cylinder and scored the cylinder walls. Could also be fuel injectors. But like Rnlcomp said, motorcraft plugs only. The 5.4's don't like other brands.

 

Thank you all for the suggestion's, but I have checked the fuel pressure at the rail, all the injectors are new and I have only ever put motorcraft plugs in it, the first set of plugs I put in two of the insulators were cracked and none of them have ever broke coming out also cylinder compression is good on all the cylinders and the valves are ok as well.

 

Is it worse when its cold, then get better when it warms up?
Or worse as it warms up?
Try checking for vacuum leaks ,
Had a ranger with a bad upper plenum gasket once causing misfires
Real bad on start up but got better as it warmed up and expanded
Did you switch the coils and plugs to different cylinders to see if it goes with the parts or does it stay in the same cylinders?

 

I'm guessing you cracked some of the 2nd set as well, gotta be delicate when installing them, it's super easy to create the situation that you are in. Swap coils from a cylinder that is not giving you a misfire code to the one or more that are, see if the code follows the coil, that'll eliminate the coil. While you have the coil off may as well pull the plug and look at it closely for cracks.
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Ok I got the truck back from the dealership they worked on it for 8 hours to no avail they said cylinders 2,3,4 and 8 are dead but they checked compression which I had already done and it was good and all the electronics were working coils,injectors,plugs etc. My scanner shows cylinders 6,7 and 8 being the problem but I'm stumped at this point maybe stuck valve, broken valve spring I'll take any and all suggestions and the problem is the same whether the truck is hot or cold, and when you try to drive it pops and cracks and falls on its face. But thanks to everyone on the reply's.

 

If you have good compression on those cylinders then you can rule out engine mechanical and start looking at the electronic control systems, the dealer should have checked it already but sounds like your dealing with noobs. There are several tests to determine an electronic issue, ALL dealers have it, it's called IDS. They can pinpoint what the problem is if they know how to use the device. Nothing I can add to help without putting my hands on.

Just on a random thought, are you in a rural area, possible for critters to chew on wires? I use to change wiring harnesses by the handful when I worked at the dealer, they love engine wiring and will gnaw thru them.
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