Been working on my 2001 F-150 4.2L 2WD EGR system for several weeks. 68K miles currently. DPFE sensor was replaced under warranty @28K. I just replaced the DPFE again and set the same code after several days of driving. Checked the vacumn to the solenoid valve - no leaks and manifold vacumn present. Installed a vacumn T into the vacumn line going to the EGR Valve and do get vacumn in varying amounts depending on load condition. NO leaks in this line either. Pulled the EGR valve and inspected for carbon build up and movement of the pintal. OK pintal movement and diaphram will hold vacumn. PUlled the EGR pipe from the exhaust manifold and EGR valve and looked for cracks and tested for blockage. Good to go again. EGR to manifold passages look clean. Set a code again. The only two things that I know of that I have not done is compare pintal movement of a new EGR with my EGR and note at what inchs" of mercury start the pintal to move. I really don't want tok remove the upper intake and lower intake to inspect for carbon obstructions unless I have to. One more bit of information. When the motor is idling, I can apply 10-15 inches of vacumn directly to the EGR valve and the moktor will run like it is firing on 2-3 cylinders for about 3-4 seconds and then will compensate for the additional EGR air, I think, and come back to close to the normal idle RPM. SLight shake remains howerever. I don't understand the Inlet Maniforld Runner Control, but I think this is what the PCM is using to compensate for excessive EGR. Any diagnostic help would be appreciated.

 

Clean the EGR ports anyway. A partial clog can put the EGR flow out of the calibrated range.

In the event they're wide open and clean, well, we'll figure that out later....

Steve

 

Sounds like my only option at this point. Thanks for your reply, and I will let you know the result.

 

Here is the result. I pulled the upper intake plenum and center section and looked for carbon problems clogging up the egr passages. What a surprise to find those 12 intake ports, 6 egr ports, and that monster IRMC and butterfly assembly. What a nightmare! Never had to work on a motor with 1/4" drive tools either, but those back 3 bolts on that plenum. Whew! Oh what fun! Cleaned everything spick and span and reassembled. Went for a test drive and on the 6th drive cycle the service engine light came back on. Boy was I !@#$@! So. Back to the shop manual and started to study pinpoint test. Bound to be an electrical problem. Open or short in a sensor or wiring harness. Guess what? The second test I performed was for the DPFE sensor and it failed! No voltage change when vacumn was applied to the downstream vacumn port. Just bought the sensor from Ford a month ago when all of this started. Took it back to the dealer, got a replacement and we are back up and running. By the way, The replacement DPFE does not physically resemble the DPFE I took back. Fourth superceeded part for this EGR system. Amazing. This DPFE has a covered vent port on the top of the case. I should have known. Heat and water---the enemy of electronics. And here we are sucking 1400+F. Exhaust gas into an enclosed case containing all kinds of micro electronics. Another case of -- looks good on paper. I think the whole system is brilliant in theory, just....... Anyway, Thanks for your response. Hope this helps you diagnose and help yourself or someone else down the road.

 

I know this is a old thread but I had the same problem and I finally found out what it was. It was one of my vacuum line that was melted onto the egr housing. It was melted so bad that I lost the front ac vents and the check engine light was reading code p401. I cut the hose and connected it with a emission hose. So far so good. Got my front ac vents working and no egr code yet.

Hope this helps someone. Good luck