Ford F150 - 1996 F150 DTC P0401 keeps popping up

I bought this truck two years ago, and have done some work on it to eliminate various codes. I bought the Hayes repair manual and an OBDII reader. I have checked for and fixed all vac leaks. I have recently replaced the cap, rotor, wires, plugs, fuel filter and air filter. I have replaced all three O2 sensors and the EGR control solenoid (only because I broke the darn hose barb getting the hose off it). I have removed, cleaned, and bench tested the EGR valve. No leaks, diaphram moves, paths are clear. Tested it in the truck by applying a vacuum and the idle changes. The vacuum from the control solenoid is good and causes the EGR valve to operate briefly when the RPMs are kicked up. The truck recently passed SMOG, albeit barely on the the low RPM side. I get about 10MPG city 15MPG Hiway. No pings, knocks, or roughness. Truck runs great.

Here's the problem: After approx. 5 start cycles or several hundred continuous miles, the MIL comes on with the P0401 fault. That's the only fault. I have my wife trained to clear it on the fly, as it gets obnoxious having the MIL on all the time. What other causes are there?

Maybe the ports in the intake for the EGR are plugged. I don't know how your engine is setup, but this how-to should give you the basics to clean them.

http://www.fordf150.net/howto/throttlebodyclean.php

crakerz
"P0401 - Exhaust Gas Recirculation Flow Insufficient Detected "
Either your PFE/DPFE is bad or the pipe is blocked.

Double Eagle
The EGR uses an external tube on the 5.0L.

Thanks for the help, guys!

While the wiring schematic in my Hayes book shows a PFE, it doesn't show the wiring to what the text refers to as the EVR - EGR Vacuum Regulator - which is the solenoid I replaced. The text also only talks about EFI systems having an EVR (the actual regulation being performed by the PCM) to control the EGR (my EGR just has a vacuum port, not a solenoid or module mounted on it). I searched for the PFE/DPFE before, but couldn't find one (I can't find a PCV either, for that matter). The under-hood vacuum diagram only shows the EVR. The Hayes book is not real helpful for my year/model. Any suggestions on a better book?

As to the external pipe being clogged, I can only say it isn't completely clogged. I will pull it apart the best I can and clean that out some more, but that brings up another question: If the restriction is further in the actual engine block, what chemicals can I safely inject to help clean it out (i.e. not kill my catalytic convertor)?

One more note that might prove useful to you experts in helping me: When I tested the system in place after replacing the EVR, I checked that the EVR was getting full manifold vacuum. I then checked the output of the EVR when the RPM's were taken up to 3500 (as the manual directs). The vacuum spiked to about 4 inches, and then dropped back to zero. When I applied the same 4 inches to the EGR manually, it did cause the engine to change idle a bit, so there is flow.

The EVR should be on the driver's side rear of the intake manifold.

.

The PFE (or DPFE) should be right in front of the EGR.



The EGR pipe should be obvious, and it doesn't go "in the actual engine block".



If you're even thinking about removing it, buy a can of Liquid Wrench or PB Blaster & start soaking the threaded ends for at least a few days before putting a wrench on them. While you're at it, buy a bottle of "anti-seize lubricant" to apply to the threads before you put them back together.

The PCV, being a regular service part, is naturally VERY carefully hidden.

Thanks for your comments, Steve. I had already replaced the EVR (only cuz I broke the hose barb ). The PCV and DPFE are not in the locations you showed, but I did finally find them.

I noticed that there was carbon buildup in the throttle body, so I removed it and the intake manifold and gave them both a through cleaning. It was then that I discovered the DPFE which was hidden behind a bracket under the plastic cover over the throttle cables. I also found the PCV, which is under the intake manifold, and impossible to service without removing said manifold, as the bottom of the manifold touches the top of the PCV! (Stupid engineers ).

After cleaning out as much yuch as I could, I put it back together and started it up. After it had warmed up and settled down, I ran 1/3 pint of SeaFoam through it. Smoked like crazy, of course, but it seems to run fine now, so I didn't screw anything up (fingers crossed) putting it back together. I am going to replace the DPFE anyway, considering I've replaced almost everything else.

Next project: serpentine belt!

Just a quick update and a big :cheer: THANKS!:cheer::bday: to those in this forum that helped . I just returned from a trip to Baja, putting 1,500 hard miles on the old girl, and no MIL!!! So, I guess it is fixed - finally!!!

I also averaged 16.5 mpg on the highway, which is better than the 12 mpg I was getting when I bought it, and better than the 14.5 mpg I was getting just last month. With gas at $3.21 on average, I figure I saved almost $30 on this trip alone. One more, and the $55 for the DPFE will be paid for.