schier1970

I am at wits end. I have 2003 f150 with the 4.6L V8.about 2 1/2 months ago it started missing. The code reader told me cyl. 3 was misfiring and bank 1 and bank 2 were running lean. I replace all the plugs, "wires" and the ignition coil on cyl 3.
The misfire code went away but the engine is still running rough and vibrates especially between 1000-1500 rpm. The lean codes are still present. I have replaced the fuel filter, replaced the injectors, cleaned the mass air flow sensor, replaced the DPFE sensor, and checked and cleaned the EGR valve. The EGR valve actuates (tested it with a vacuum pump), so I do not beleive that is the issue.
I have also unplugged the rear 2 O2 sensors to see if it changed anything. A code appeared that the O2 sensors were not sending so I plugged them back in. Due to this I donot think this is the issue either.

So again Help.

Hit-By-Thunder

sounds like the vacumm leak from the EGR. These trucks are famous for this, especially with the banks 1&2 running lean. Unmetered air is entering the engine.

Take some carb cleaner/throttle body cleaner and spray it behind the throttle body area and see if the engine rpm's change. If it does, that is where the leak will be. I would start there first though.

Rob/HBT

Domenic A

I had the samething bank 1&2 lean, i found a split in the pvc hose. Replaced it and everything is good. It was on the bottom of the hose hard to see, with the engine running carefully start grabing rubber vacuum hoses to feel for leaks.

Hit-By-Thunder

sorry about that, it was the pcv NOT the EGR, my mystake, sorry and thanks for pointing it out Domenic

Rob/HBT

schier1970

I have made a discovery. Apparently some one changed out the motor with a 1999. All the parts that I have been getting match a 99.

While I have been looking at parts, I got to thinking. Is there a vacuum pump on the truck and does it also assist with the brakes. I have noticed lately that once the truck is warmed up and the motor is running rough, you have to press the brake pedal alittle harder. This is happens off and on. Could they be related??

kookookachew

When pressing the brake pedal, does the idle change at all? If you haven't noticed try and start the truck and when its idling pump the brakes and see if it changes the idle at all. Sometimes the vacuum brake boosters develop small holes/cracks in the diaphragm causing a vacuum leak, and if they are bad enough the can cause poor running quality.

losbagres

Schier1970: Replace: the (Two flying saucers look alike) which I saw on a different ford, locate them first probably attached to same (hose look alike) then while on ON delete the engine light with the OBD II
run it for a month if it doesn't come on, you're home free!

00gstang

test for vacuum leaks (especially the PCV hose) and check the o2 sensors (the "probe" on them might be covered in gunk causing them to fail)

seraphim

This. Just this week I was having the same problem. Found a massive hole in one of the vacuum rubes.

harm63

I agree with everyone else...it's gonna most likely end up being a vacuum leak... I just fixed this issue on mine (5.4)... I had a vacuum line going into the back of the intake that I didn't realize was unhooked...before I'd start spraying your hoses with carb cleaner or anything to see if the RPM's adjust...just "listen" to your engine for a little bit....that's how I ended up finding where the leak was coming from... you'll know it when you hear it (depending on how major the leak is)

just my two cents