First thing first.
I have been on this site for a long time and I have learned a ton from you guys. You have saved me a load of money too!!
I have been trying to fix my p0401 code for months now. I know I have a vacuum leak because when I am going up hills my ac goes through the defrost.
I replaced all the lines under the dash and behind the battery. They were dry rotted so that was no big deal. I cleaned the maf and the throttle body. I replaced the PVC? Line behind the throttle body and also replaced every rubber elbow.
I'm at a loss right now. I have to get my truck smogged next month and I need to figure this out... I have done every thing I have read on this site and I still have no luck. I'm sure there is also something's I have done that I have forgotten to put here.
If anybody could help me out I would really appreciate it. Like said before I don't know where else to look/replace
Thanks

 

The P0401 is an EGR issue, specifically insufficient flow. The most common cause on the 4.6 is plugged EGR passages in the throttle body. Other possibilities are a bad EGR valve or bad DPFE.

http://www.obd-codes.com/p0401

 

Sorry I cleaned the egr. It was completely plugged.
Would a bad dpfe cause a loss of vacuum?
I replaced the lines going to the dpfe also.
I guess next would be to replace the dpfe itself. But I don't know where else to look for the vacuum leak I have.
Thanks for the reply glc!

 

Did you clean the throttle body passages? Does the EGR valve pass the "suck" test?

 

On my truck i had a frayed small black plastic vaccum line going into the firewall on the passenger side. cut the bad part out and put back together and the AC stopped blowing through the drefroster vents.

 

Glc- yes I have cleaned the ports and it does pass the suck test.
01 gt F150 - is that the plastic line on the fire wall by the battery? If so I replaced the entire line from behind the battery box all the way into the cab under the dash.
Thanks for the replies guys!

 

If you are still getting a P0401, you probably need a new DPFE. Stick with Motorcraft, aftermarket DPFE's don't last.

 

yep, that was the one.

 

Thanks glc I'll order one and let you know what happens.
01 gt F150 yeah that was the first thing I fixed. I guess I'll keep on searching and pray that I find it!
Thanks again guys.

 

Carb cleaner sprayed on vacuum connections can help you find the leak. If the Idle jumps up when you spay an area theres your leak.

 

Carb cleaner can also eat the vacuum hose.

 

Sorry for the late response. i have been swamped with work and have had zero time to work on the truck.
I'm going to order a new dpfe and go from there I am hoping this solves the engine code problem.
And as for the vacuum leak I don't want to use carbon cleaner because as stated before it will eat away the lines.
Is there a safer way to check for vacuum leaks?
Thanks.