So my 2001 5.4l 4x4 f150 has been acting up for months I've changed the pcv valve the iac valve taken the throttle body off and cleaned it and my whole electrical system failed as well as my ac I replaced the starter the alternator and the battery twice! My truck is running very rough it idles low at about 500 rpms it feels like it's lagging in power and has very very minimal acceleration it runs okay.... below 105-110 degrees but if it gets much hotter than 105 out which it does a lot being that I live in Phoenix my engine really starts to struggle if I drive more than 15-20 minutes stopping and going a lot it will start to lose all power and misfire until it stops running and my power steering locks up then I usually have to try and get it to start and most of the time I have to let it sit for 10 minutes then start it back up and it'll drive okay for a little longer. When its struggling and I'm trying to start it up or mash on the gas pedal it feels like it has no power pedal to the floor and I'm going 5 mph at most then i start to hear loud popping noises from what sounds like the drivers side of the engine bay and it'll rev back up really high and jump forward and be okay when I am at a stop in any weather or no matter how long I drive it it won't rev higher than 1500-1800 rpm.... I'm looking for any advice I can get I know there are a lot of different things that could be wrong so I'm trying to narrow it down before I spend money fixing 10 things before I get to the root of the problem.

 

You have a vaccum leak. Check the hose coming out of the back of the intake manifold and chase it to the pcv on the passenger side valve cover. It has 2 small radiator or heater core antifreeze lines hooked up to the piece that's on the back of the manifold. That elbow back there gets holes in it. Its hard to find and hard to hear it sucking air so check there 1st. And then Run the truck And then i would just listen and touch all the rubberhose to find the leak. Replace all the hoses that are cracking or that leave black stuff all over your hands.

 

You say you replaced the PCV valve..... what about the PCV pipe/hose assembly?

EDIT: Looks like Duce already said that. So I second his words.

 

And your DTC's are P0171 and P0174..

 

Good catch... I didn't notice that.

 

Disregard your DTC's, - has nothing to do with problem....a by-product of another issue most likely.

It's the 500 rpm post and your description that narrows down the possibilities.

Fuel first - it's like a tech by-law, always check fuel pressure when it's acting up. This will rule out a fuel delivery problem pronto.

Most likely causes, one of two things or both because the first one can lock the EGR open.

1. You have a blocked converter which is like shoving a potato up your tail-pipe.

and/or

2. The EGR valve is stuck open which is like shoving a potato into the throttle body. The engine is sucking exhaust gases from the drivers side manifold vs clean filtered air from the intake.

Below 700 rpms you have an obstruction. You post 500 rpms, so sure enough. You need to harvest those potatoes.