I have a 04 5.4 that's misfiring in OD between 1200-1500 rpms under a load. Its been getting progressively worse. My truck has 133k on it. The plugs were changed at 100k. My concern is that it's been doing this for about 2 weeks and hasn't thrown a code. Is it possible since its not thrown a misfire code that a clogged cat or something else could be causing this? I just don't want to replace all the coils and not fix it. I wish it would throw a code so I could see which cylinder is misfiring and switch the coils to see if it changes the cylinder it's mid firing on. Is there any way to test the coils? Thanks

 

Mine was doing the same thang. It finally threw a code on cylinder #1. I replaced that one coil and it was fine for a few weeks and started again. I replaced all 8 with accel coils and running good so far.

 

Check the condition of your FPDM...located on the frame near your spare tire...remove it and look at the backside..

 

Don't rule out your fuel injector.. The 04/05's had an issue with injectors sticking open under load and creating a misfire condition. If you really lay into the gas I would expect to see a hard misfire (flashing CEL). If so be careful you could be doing damage to the cats.

 

I'll check the FPDM this afternoon. I feel like the issue might be at least partially fuel related. It hesitates and kind of sputters when I lay on the gas hard up to 4000 rpms and then clears out. I've already cleaned the MAF an have a new k&n air filter. I had the gotts mod but changed it back to stock until I get it figured out. It isn't having and really hard misfires yet and still isn't throwing and codes and the CEL has not lit up. I do have pretty loud injector ticking though

 

Got home from school and pulled the FPDM off and found that its cracked and corroded pretty badly. Think this could be the issue?

 

That could be the culprit. Couldn't hurt to replace anyways as it may leave you stranded one day.

 

Got home from school and took the FPDM off. It's corroded pretty badly and the housing is cracked all the way around it. Think this could be the problem?

 

Yep !! that would be a good start..

 

Just ordered a FPDM with the spacer bolts to keep it off the frame