Magas

well , I learned a lot reading the posts here in this website. and that's how i fixed a bunch of errors I was struggling with.
I did have these errors :
( Error P0171 , P0174 , P0302 , P0304 , P0401 , P0442 ) which seems to disappear after changing the :

spark plugs + wires
fuel filter
DPFE sensor
coil pack
Gas cap
both O2 sensors on bank one (passenger side)
Note :my EGR valve is OK !

as you see I had several errors which seems to be cured. the only remaining error is P0171 . and now the truck is knocking and hesitating either in idle or driving.
please help me get over this nightmare ...
Thanks

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F150 2001 6cyl 4.2L 2wd ---- 220,000 miles !
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Magas

I should add that I took the MAF sensor out and measured it , also IAT and they measured fine ...

NGM

The first thing I would do is look for Vacuum leaks. That is a lean code, as I am sure you know. You can use carburator spray and spray around the base of the intake, all the vacuum lines etc etc. Make sure the crankcase breathers are all hooked up. Check the PCV valve make sure its in its place. After that its time to start checking your fuel system. This is where it becomes a PITA. Pull the rail with the injectors and make sure all of them are spraying. This is not the safest way, but without all the test tools its the easiest way. With as rough as it is running I am suprised you are not getting a recurring p0300 code.

msteele516

Well the fix is not going to be easy. Follow the course the moderator above me suggested first. Then if you haven't isolated the problem, brace yourself for some interesting wrench-twisting. I jokingly referred to it as a 10 min job that takes 2 hours. It will take every bit of that! Take a vacuum reading at the plenum and see if it is less than about 20 in/hg. If so, you probably have a gasket leak underneath the plenum. Start with a cool engine cause you will brand yourself if not. Label and Remove air intake snorkle, and all plug-ins to plenum. Remove throttle linkage. Release spark plug wire keepers at each corner of the plenum near the firewall. (They pull straight up off the post once released.) There is a sound-deadening pad that is between the plenum and the firewall. Cut slits at the narrow points on both sides and remove (you can spend an extra 2 hours and remove the fasteners if you have gobs of time.) Now you can get your hand/tools to the back side of the plenum to remove the 10mm bolts that retain the clamshell top. Remove the top of the plenum. Be careful with the o-ring seal around the perimeter of the top. Inside is a series of baffles. Remove the screws retaining the baffle plate. Underneath that plate are 6 brass-appearing orrifices. These will all be clogged from EGR gasess. Clean them. You may have just fixed the problem at this point as that took care of my trouble code, however since you are this far along, and if you had a low vacuum reading, you might as well replace the intake manifold gasket underneath the lower clamshell part of the plenum. Most are factory-cracked. Saves time cracking them in the field! Replace this gasket and re-install. Good Luck. Let me know if this helped.

Magas

Thank you very much for the replies .

1- as i asked before : does PCV valve need to be too tight and secure or it's normal to be little loose in place. I did not find the pcv grommet to change it.
2- catalytic converter : I smell rotten egg while pushing the accelerator . I heard it could be the catalytic converter . is it difficult to change ? is it possible to be the cause for p0171 ?

thanks a lot .

NGM

If you think its the convertor clogged up take the front 02 sensor out and try running the truck. The PCV valve should fit snug in the grommet.

Good old Bill

I like and agree with msteele about the intake plenum. Not to sure about the other codes and cures. The P0171 and P0174 codes are generated because the engine senses a lean mixture. I finally did the work this morning on my 02, 4.2 that would throw the codes on early morning start ups in cold weather. Have gone since January and no codes or running problems. Believing what the techs are telling me, I changed the necessary parts this AM. All the rubber seals need to be changed. Six of one style, one large seal or O ring and also there are 8 bolts with built in grommets attached. Original grommets were black in color, new generation is green. Some improved type. Reread what steel said about the procedure and it will take 2 Hours. 1/4 drive socket set a must, 10mm deep and short sockets, and a couple of others. One last thing, there is no PCV valve, or at least I didn't have one. Have fun!

Magas

quick question :
is it possible to get the code P0171 ( lean error ) as of a faulty or clogged catalytic converter ?
I took a test drive with my truck and noticed the lack of power and severe stumbling and hesitating .... I can also smell the gas or burned oil, engine components get so hot and noises due to vibration ...
Note : I have not started working on plenum yet.

Thank you guys . You are the bests !

Good old Bill

I was always under the impression that a cat would plug up from to much fuel not because it was running lean. But strange things do happen.

Magas

Heyl ; any idea what gasket to change ? "Intake Plenum Gasket" or "Intake Manifold Gasket" ??