P0401 after plug change

[Red97EBV8]

I just replaced the plugs & wires on my 97 V8. For all my hard work (the plug wires were a pain) I was rewarded with a CEL after about 10 miles. I scanned it and found a code P0401, Insufficient EGR Flow. I searched here for info and found a lot of references to the DPFE sensor. However, I can't find anything in my engine bay that looks like the descriptions I've read of a DPFE sensor. I also read that 96 & 97 V8's may not have DPFE sensors. So, my questions are:
1) Why would I get a P0401 after changing plugs & wires?
2) Does my 97 V8 have a DPFE sensor?
3) If not, what would cause this fault code?
4) If I do have a DPFE, where is it located?

Thanks.

Billy

 

[dogfriend]

Check to make sure that you didn't bump and knock off a vacuum line or hose while you were changing the plugs. Also, especially if the hoses seem brittle, check for cracks in one of the hoses. Item 2 is the backpressure transducer which would give the signal of insufficient flow.

 

[dogfriend]

You should have a sticker like this one. Check all vacuum lines, especially the ones connected to the EGR components

 

[Red97EBV8]

dogfriend,

Thanks for info. I figured that I could have bumped a vacuum line, but I couldn't find the EGR valve, or any of the controls. My Ford CD occassionally doesn't want to run on my XP machine. It's working this morning, and I was able to find the diagrams you showed. BTW, how do you capture images from the Ford CD?

Thanks.

Billy

 

[dogfriend]

I'm using a Mac with Virtual PC. It has a screen capture function that transfers the picture to the Mac Desktop. I crop and resize them and convert to jpeg using Adobe Photoshop Elements (they are too big to post otherwise).

I would imagine that you should be able to do a screen capture in XP.

 

[Red97EBV8]

I've read that at least 90% of the time, an EGR problem is caused by a problem with the DPFE. Would that also be true for the backpressure transducer?

Thanks.

Billy

 

[dogfriend]

Fords with an EGR system usually have a DPFE or just an PFE. I think that it is possible that the one on the 5.0 could be a PFE. I don't have the info with me right now cause I'm at work.

Anyway, yes, I have seen a few threads where this code is caused by the DPFE. But it is possible that your EGR valve isn't working right because this is the condition that the sensor is designed to detect.

I would try to rule out a leaking hose first since the problem seemed to correspond with changing the plugs. If you can't find anything else, then the DPFE could be the problem. There are tests that you can run on it. I don't have the test with me, but I could post it later if you need it.

 

[Red97EBV8]

dogfriend,

I didn't realize that you went to so much trouble to post an image. I owe you a bigger thanks.

I didn't have a lot of time to look at it last night, but I did find all the pieces (EGR valve, transducer, and solenoid), but they didn't look like the diagram. As compared to the diagram, my EGR valve is rotated 90 degrees toward the rear, and it's on the opposite side of the solenoid. There must have been a mid-year change. Would anyone happen to have a diagram for a 98? I still can't quite figure out how all the vacuum lines are routed. I can't trace any of the vacuum lines to anywhere near the spark plugs.

Thanks.

 

[dogfriend]

Here is some more info on the DPFE/PFE. It is out of date for your truck, but you may be able to test to see if your DPFE or PFE is bad.

Edit: I resized it to make it easier to see.

Look below for PFE2 for the electrical tests

 

[dogfriend]

Also, here is some info on the other EGR components:

EVP

 

[dogfriend]

EVR

 

[dogfriend]

PFE2 Electrical tests for DPFE/PFE

 

[Red97EBV8]

Dogfriend,

Thanks a bunch for the images. You've been a great help.

I tested the EVR per the procedure above, and it passed. I realize that the test is probably not 100% reliable, but it's better than nothing. Next, I tried to remove the vacuum line from the EGR valve so I could test it with my vacuum pump, but it was dried out and brittle. If I had continued, it would have crumbled. I'm going to get a replacement before I remove it. But I did try to exercise the EGR valve. I had a helper apply about 1/3 throttle with the truck in reverse while holding the brakes. Shouldn't this make the EGR valve move? This procedure worked on a another vehicle I have, not a Ford. The EGR valve didn't move. Next, I'll replace the vacuum line, and repeat the test.

Billy

 

[dogfriend]

I don't think that your test of the EGR valve is valid, based on what I have read in my Ford Fuel Injection book. The EGR valve only opens under specific conditions, usually only during 'warm cruise' or 'warm driveaway'.

The book says "The control module operates the EGR valve only when it receives all the following input signals:

- Warm engine signal from ECT
- Part throttle signal from the TPS
- Part-load signal from the MAF or MAP
- Time since start, from the timer in the control module "

The signal from the MAF might not be correct if the truck isn't actually driving down the road. Also, the time since start would probably not be right either.

I think your brittle hose is a clue - replace the vacuum hose(s) and clear the code to see if it comes back.

 

[Red97EBV8]

It's Fixed!!

Replaced the brittle vacuum hose and cleared the P0401. Driven it about 10 times and... NO CEL!!!

I still don't know how that hose got damaged during a plug & plug wire change. I recently replaced my heater plenum (broken blend door) and I was all over that area then. But the plugs & plug wires are nowhere near the EGR system.

dogfriend, thanks for all your help.

Billy

 

[dogfriend]