Looking for suggestion or help on my 1997 f150 4x4 5.4l engine EGR system. About a week ago the CEL came on. The code reader showed the 0401 code. I hooked a vacuum line to the egr valve and supplied a vacuum to it. It began idling rough and immediately returned to normal idle when the vacuum was released. I concluded the egr valve was working so without testing just replaced the DPFE sensor. After resetting the CEL drove the truck about 15 miles and the CEL light was back. Checked the DPFE sensor with my multimeter. Voltage at idle was about 1 volt. When vacuum was applied to the EGR valve it rose to 3.5-4 volts. So the new sensor looked good. Pulled the two vacuum lines off the EGR regulator sensor and checked for suction. Didn't feel any, so I hooked the vacuum gauge to the source line and revved the engine to 1500- 2000 RPM's. Did not move the needle. Am I correct in the thought that the source line to the solenoid should have a vacuum and increase when the engine revs up? With that thought, I traced the vacuum line to the passenger side firewall and a plastic junction block. I disconnected the line from the block to the solenoid and applied vacuum. That line checked good and held the vacuum. From there it appears the line goes behind the battery and into the fender well. This is where I am lost. Where does the source line go. Where to check it next? Is my thought process correct or am I going insane for no reason. HELP!

 

I googled p0401 ford and came up with several youtube videos about how to diagnose and repair such as

 

Thanks Roadie. I realize this is a common problem with the F150 intake ports. I have this option in mind, as a procedure to try. I guess my question is though, my EGR valve seems to operating correctly when tested manually and the DPFE sensor seems to be doing its job, so shouldn't there be a vacuum on the source line at the EGR regulating solenoid? If so what and where is the source of the vacuum and where do I check it next?

 

Have you pulled the throttle body and cleaned out the EGR passages in the elbow?

 

Thanks for the reply. No I have not cleaned them yet. Had a garage tell me the intake manifold had a leak. I was skeptical but had them replace the gaskets. $300+ dollars later and 10 minutes down the road the CEL light came back on. Wouldn't they have noticed the throttle body ports if they were clogged? I guess I am back to my main question " Shouldn't there be vacuum in the source line to the Egr regulating solenoid?". It's the solenoid and the DPFE sensor that controls the vacuum to open and close the EGR valve correct? I guess I don't understand how clogged throttle body ports would effect the source vacuum line to the EGR solenoid? Someone explain? Lost.

 

Seams like everybody is out to lunch on this even your shop
What is EGR? It stands for exhaust gas re circulation.
.
Why is it there? To reduce combustion chamber temperatures in that part of the drive cycle the motor most spend time at and to reduce nitrogen oxide emissions, as required by federal law.
Exhaust does not burn the second time in this feedback, so cools the existing charge by 'polution'.
.
This action has nothing 'directly' to do with vacuum except that the exhaust is under some pressure, the intake is drawing at the same instant of the test and functioning helping the flow rate.
.
Intake vacuum is supplied to the vacuum regulator as a control function only to open the EGR valve.
The command to open the EGR at the correct time is computer controlled.
The computer program has several tests it does on this system.
One of which is a Flow test under controlled conditions.
It opens the EGR then uses the DPFE to measure the flow drop across an orifice inside the metal tube. The DPFE reports the reading to the computer as a pass or as a fail setting the code 401 for that specific test.
Anything that prevents or restricts the flow from being established is logiced a fault and sets the code and CEL..
You see why you are not getting a handle on this simple procedure?
Vacuum hose to the EVR, hose to the EGR, DPFE electrical plug up and it's hoses to the metal tube between the exhaust manifold and the EGR valve.
Any failure in this chain and many tests will fail.
Good luck

 

Thank you Bluegrass. At least I have a little more insight into my confusion. I have decided to pull the throttle body tomorrow and check and clean. Hopefully this will eliminate any restrictions to the flow and provide the needed vacuum to the EVR? I guess
time will tell. Thanks again.

 

Good to do that on an elderly engine but it likely won't change the situation.
You see the intake vacuum is the highest near closed throttle or low throttle openings at elevated rpm.
Only time it is higher in under sudden closed throttle when the engine RPM is high. Then it can go as high as 23 + inches of vacuum for a short time.
Good luck.

 

I think I will continue tracking the source vacuum or lack of it , before cleaning the throttle body.

 

After reading Bluegrass's last post, I tried attacking the vacuum issue from the source end.I hooked the vacuum gauge up at the throttle body and got a 20 in. reading. Next checked the source at the plastic junction block by passenger firewall. The line checked good to here. I guess my next quest will be to figure out how to gain access to the passenger side inside fender well and vacuum reservoir where the source line tees to a vent and source line returning to the Egr solenoid. I think?

 

I think you should clean the passages in the throttle body elbow anyway. After 20 years I can almost guarantee that they are plugged. Remove the throttle body, then remove the elbow. There are 2 ports and you may not even see them unless you look carefully, that's how plugged they get.

 

Well I think I found the source of my vacuum leak. Tracked the vacuum lines to the reservoir in the front passenger fender. All the lines to the reservoir checked good on the vacuum gauge. Took the tank out and found one small hole and a larger hole on the topside of the tank. Awhile back I bought a new radiator core support with intentions of changing out the rusted one myself. To make the story short I ended up taking it to a body shop. Well apparently they left some jagged edges where they cut out the support and they wore two holes in the plastic tank. I am betting this is most of my problem. Won't know for sure until I get a new reservoir and get it back together. If I am experiencing problems after replacing the reservoir, I definitely will clean the throttle body. If she run OK and no CEL, I'll still clean the TB next summer. We'll see what happens!