CEL came on while back, I drove it like this for months, until the loss of power in acceleration was so bad it felt like I was driving a 4 cylinder Honda. COde run, P0171/P0174.

This is a V8 2003 F150 4.6L EFI.

I cleaned the MAF, checked air filter, replaced fuel vapor hose, replaced EGR valve/sensor, replaced DPFE sensor, checked for vacuum leaks. Cleared codes, no luck.

Took to a City Garage first time, they said dirty fuel filter, so I said go ahead and change it. Did so, cleared codes, and 20-30 miles later, CEL is back on.

Took to a City Garage second time, they said fuel pressure was in low 20's and throwing off the fuel trims all over the place.

I replaced entire hanger assy/strainer unit with a new Carter pump. Walah! No more horrible power loss in acceleration and idle issues!

After about 20-30 miles, CEL comes back... code run, P0171/P0174 still.

I have a rough idle when I reverse out of my parking spot every morning. But once I start going, everything is fine.

Where do I go from here?! I thought it was weird the fuel pump fixed a large chunk of the issue, but it still remains on the same code. Is it possible the lean running fuel pump damaged other components from months of fuel starvation? What would be next in line to fail from what I have described? It was apparent to me the shop was running on "replace it til it fixes it" mentality which my wallet cannot support, hence why I've been doing all the work myself.

 

You sure you don't have a cracked or soft PCV rubber elbow behind the intake?

 

PCV system, - they usually leak between the firewall and throttle body elbow.

Also, check the trans fluid, - rewind can take allot of pressure and fluid. They can and have stalled, if the trans fluid gets to low.

 

Didn't see your post glc.

 

I replaced the line behind the intake already a while back, and then checked it again when I checked all of my lines/valves. Those all appeared fine to me.

 

The 171/174 is both banks.
The codes tell you there is likely a common air leak into the intake tract.
The codes are set when the fuel tables shift out of limits on the 'rich' side trying to correct for excessive air.
The issue is there, you just have to find it.
Good luck.

 

Did you clean your throttle body?

 

yes, I cleaned the TB when I did the MAF sensor.

 

Check your brake booster line also, it can give the same codes as the elbow being bad. Also if the booster is bad, same story.