Issue with 2004 expedition 5.4

Hello I’m new to this website and I’m very glad I found it. I’ve looked around here and found some things that could be the root of my issue but I’d figure I’d ask. First thing is it’s having a run in lean code on one bank and then a rich code on the other one. Along with a misfire on cylinder one. Now I’ve used a homemade smoke machine and fixed one leak. Now the new parts I’ve thrown at are fuel filter, egr valve, bosche injectors, motor craft ignition coils, mass airflow sensor, air filter. Now the problems I have driving, on the highway it has slow acceleration and don’t even think about passing people, here recently it has a hard time starting after I’ve driven around for a bit then parked, but a cold start in the morning or at lunch it fires right up. I plan on buying an actual smoke machine. Any help would be appreciated

Have you checked or replaced the oxygen sensors? What code numbers are you getting with the OBD II scanner? Check engine light is on, right?

Check your vacuum lines. The small black hoses & the Rubber elbows that attach to the aluminum engine parts.

Try This for reference: 2003 Service Manual
2003/2004 setups are very close

After checking for vacuum leaks, the first things I would check are the catalytic converters and O2 sensors. Also, if you are using aftermarket vacuum hosing, make sure it fits together tight (I got burned by this). You should also check to see if the intake manifold is bad, which will cause serious vacuum leaks - one way to check is to spray water (with a spray bottle) on the seam between the manifold and the heads on both banks, and observe if it the engine runs any differently. The manifolds on these often only last about 150k (140k for me). Lastly, check for coolant leaks (from the manifold or hot water controller for example) that might flood the Cyl1 coil. There are youtube videos on how to check all these things. Good luck.

I had similar power loss issues with an ‘03 EB 5.4 that I recently bought. Cylinders 1 & 5 were misfiring. Replaced all 8 plugs and COPs. Fixed the misfiring, but still significant power loss. Replaced the intake manifold, and a few vacuum hoses that were shot. That gave me a chance as well to properly fix the water pump stem leak via the mod.

Starts and runs great, but still power loss. Suspected the cat(s) were no good with all the fuel being dumped in there from the cylinder misfires. Turned out I only needed to replace one cat. Now she runs like a top with 260k on the clock.

Clogged cat. My 05 did that. Completely melted down. Left side. I got one from rockauto. Has been in for 6 years now no issues.