My F-150 (2003) doesn't want to accelerate once you shift into 4th gear. It starts shuddering and doesn't really respond no matter how much you mash the pedal, and in 5th gear it doesn't accelerate at all. Engine is giving off lean codes for O2 sensor banks 1 & 2, sensor 1 (both banks).

What I've done so far:
Replace spark plugs: when I first did this, I noticed two or three of the plugs were scorched white. After replacing, performance improved for about a day, followed by a return of all symptoms.

Replace O2 Sensor 1 on both banks:
Sensors were white to orange in color. Again, after replacing, performance improved for about a full day before previous symptoms returned.

I'm thinking clogged fuel injectors (haven't pulled them off yet). Any opinions?

 

It does sound like your engine is starving for fuel.

Immediately, the fuel pump comes to mind. I would check your fuel pressure readings to start with.

The next concerns would be the fuel filter, fuel pressure regulator, then the injectors.

 

definitely sounds like a fuel issue of some sort. Since you've already replaced all of your spark plugs and the o2 sensors... yet still have both banks running lean.. have you replaced the fuel filter at all? I personally had the "bank 1 and 2" lean and it was my intake manifold gaskets that were allowing throwing off the computer and causing the truck to run rich. Make sure:

- air filter is good to go // make sure the fuel filter is changed

something else to consider... does your truck have a hard time starting? that'd indicate a failing fuel pump as well given your situation.

 

Have you replaced your isolator bolts and intake manifold gasket? Those are known to be faulty and can cause a vacuum leak that will cause engine to run lean on both banks.

 

I just solved my 171 and 174 issues. What it took:

- New fuel filter. Was crudded up. Fuel pump tested fine.

- New 02 sensors, both tested dead.

- Exhaust manifold had the common broken stud problem, so I had the ticking problem. Manifolds were warped, so I replaced them with shorty headers. *Note, I didn't need headers, but they are shiny, and I like that. *Note, this may not have been a necessary step to solve the problem, but I wanted it done because I didn't like the ticking noise, but if you are just trying to solve the issue, do this last.

- New bridge hose on the vacuum line that goes to driver side valve cover. Under the plastic trim piece that says 5.4L Triton. was all rotted and not sealing. Looked like foam instead of rubber, and turned my hand black to touch. 4" of fuel line replaced it. I *think* it was 3/8, but I just had them match the ID at auto zone.

- New Vacuum line that goes from the top back of the throttle body over to the "whatever it is" with the green pinch clamp by the evap test line. Same foam look. 2 feet of gas line did the trick, again, I think it was 3/8.

- Cleaned MAF with QD Electronic cleaner (aerosol). They make a MAF cleaner, but had this handy.

- Just for giggles, I threw in a new pcv, because it was 3 bucks.

Runs smoother now, no codes for the last week.

 

Can you describe this ticking? I think I might be having the same issue.

 

Sounds like one of the converters is plugged IMO.