Hello everyone,

I recently purchased a 1997 F150 Supercab with 4.6 auto. The check engine light is on and is giving me the p0401 code indicating insufficient EGR flow. I took the throttle body off for cleaning as I have learned that this is a common problem with these trucks. When I took it off the egr ports were cleaned and i saw no blockage at all, I gave it a good cleaning anyway and put it back together, I cleared the check engine light and it came back shortly after with the same code. I then checked the egr valve which appears to test fine, I tested the DPFE sensor and it tests good. I then disconnected the two vacuum lines from the EGR solenoid and started the engine to check for vacuum, there is no vacuum being supplied to the egr solenoid. I then traced the white colored line and I followed it to the passenger side of the vehicle where it connects to a junction box behind the battery then continues through the fender where it disappears. I did find two sensors on the firewall near the battery with two vacuum lines attached to each, im not sure what there function is or if it has anything to do with egr but a tan colored line coming off of one of them is broken, this is the only thing I can find wrong with the system. I used light compressed air to test the integrity of the lines and air always passed through, I check the main vacuum line coming off the manifold and it is creating vacuum as it should, its just not getting to the egr solenoid. I have hit a wall with this not sure where to turn, I have attached a picture of the broken line and the junction box which has room for five hoses with only three attached (not sure if this is an issue or not). Any feedback would be much appreciated, Thanks!

 

Pick 1, - your 4wd vac line is broken.

Pick 2, -your trunk line is disconnected, - totally.

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Are you absolutely sure you cleaned the EGR ports on the plenum ? You have a pick of it ? They're easily missed on the 4six.

BTW, your EVR and EGR should show very little vac at the green line. Not enough to open the valve anyway. It doesn't pull vac until the PCM commands it at cruising speeds.

Is your EGR pipe leaking at the manifold ? That can produce a PO401 as well.

 

Thanks for the reply!


The truck engages in and out of 4wd as it should, should it still work without this hose? On pic#2 if your talking about that junction box thing it is hooked back up now I just took it off to inspect it. I did a lot of research on the throttle body egr ports so I made sure to inspect and clean them thoroughly and I feel certain that they are clean and free flowing. I checked the white line going in to the EVR and it has no vacuum. From what I understand this line is supposed to have constant vacuum going to the EVR and it then regulates vacuum to the rest of the system. Correct me if I am wrong on this cause if so I am going in circles. After further research I now suspect the EGR canister that is supposedly located inside the passenger side fender which will be a pain to get to. I can't really find anything online about it other than another members post on this site.

 

If you plug your fault code into the SEARCH box, you'll find hundreds of prior posts and threads discussing it... It's been an FAQ for years.

 

I found a lot of valuable information using the search function (on here and google) which is how I made it this far by learning all the components of the egr system, how they function and how to test component and troubleshoot the system. Most everything I have found is about sensor malfunction which usually cures their problem. All these things check out on mine except that the evr is not getting vacuum as it should. It seems that this may be an unusual problem and I cannot find information about this specific problem. My truck is getting horrible gas mileage around 8-10 mph normal driving and I think its due to the non functioning EGR system.