I've been diagnosing p401 problems. I believe I have a bad vacuum regulator. I'm pretty sure I should not have 12v to both sides of the plug with just the koeo or when no egr is called for. Doesn't this tells me that the vacuum regulator is bad? Just need some confirmation.

 

A good solenoid will show voltage in and out....until....the PCM completes the ground path...at that point...the solenoid will function and the voltage should drop on the PCM side of the connector...

 

I replaced the solenoid and still have the same problem. I
did attach a multimeter to the pcm side with a long lead to inside the truck so I could read it. I also did the same with a vacuum meter. I had about 14v on the meter from the pcm side when the motor was running. For about 5 min.s after I started the truck (engine was at operating temp.) As I accelerated I would get a drop to about 7-8v and the egr vacuum would rise to about 6-7 ". This would go away when I let off the accelerator and the voltage would return to 14v as it should . The problem is it would stop after a few minutes and I would never see a drop in voltage or an increase in egr vacuum until I turn the truck off and started the process again. Do you think this is a pcm problem? It works
occassionally.

 

There's nothing wrong with either the PCM or the EVR solenoid.

Did you do a "suck" test of the EGR valve to verify the valve operates and the inlet passages are clear? If so, did you measure the DPFE output to see if it is properly measuring the rate of EGR flow?

Please keep all related conversations in the SAME thread.

 

EGR ports are clean, egr holds vacuum,vacuum on egr while running creates rough idle , enough will kill the engine. New motorcraft dpfe. Down
tube is clean and new vacuum lines to the dpfe. For some reason the pcm
stops sending signal to solenoid after 1-2 miles of first start. If I cut the engine off it will repeat the cycle. I tried a new vacuum regulator and the same thing happens. 22" of initial vacuum to regulator. I checked voltage on the pcm side of the regulator. When egr is not called for I have 14v.
When (for the short period of time I get vacuum to the egr) I get egr vacuum it drops to about 7-8v. Then , as stated , it goes away after 1-2
miles.

 

First thing you need is to understand the operation of the EGR and when it is called to operate.
Assuming the 401 code is the only code you have involving the EGR system, it is a 'low flow' code.
Operational voltage at idle don't mean much unless it is absent.
Solve for the 401 code first.
It has to be one or more of the following.
Blocked EGR port.
EGR fault.
Regulator fault.
Or the DPFE cannot report the results of the test sequence.
You cannot force EGR operation unless you are at a speed above 45 mph, have light throttle application and a short time at near a low constant throttle angle.
This is all PCM controlled. You cannot influence it by tricking.
The EGR system does not operate at any other time except under PCM test conditions as written into the program.
.
You already did the EGR vaccum test and indicated the motor idled rough. An ok result indicating the flow rate is possible.
The VAC reg is a 3 port device with a sponge filter under it's cap. Be sure the filter is clean and the solenoid operates without sticking at any point and the hoses are on the correct ports. Note: there is a filter because outside air must be let in to allow the EGR to close again after it has been opened by vacuum.
If all is well, you need to suspect the DPFE cannot report the results of the system pressure test.
Thinking about it any other way will only cause confusion.
Good luck.

 

By now I know the egr system inside and out. That's why I'm confused. lol
Everything checks out. The only thing I can think of at this point is I put a new motorcraft dpfe sensor on that is plastic. I've been reading and some say that because my original was metal that the plastic sensor could have a different vref signal.

 

Have you used your scan tool in mode 06 to read the DPFE_PID while applying measured vacuum to the EGR valve? That's one way to test the system.

As far as the voltage on the solenoid, the PCM commands a variable amount of EGR flow by using a variable duty cycle application of the ground side of the coil. That's why you read batter voltage when the EVR is not being commanded to open. The variable duty cycle is why you read some voltage around 7-8 volts when you mesure it with a DC meter. Use your scan tool again in Mode 6 to monitor the EVR's duty cycle PID.

Your voltage and EGR vacuum "goes away" because the PCM has either aborted or failed its self-test monitor for the EGR system, causing the EGR system to be "turned off" for the duration of the drive.

 

Finally some headway. Since I let a repair shop install some new parts , including the new dpfe and I
checked everything else, I decided to go over their work. I Found that the new vacuum lines were installed backwards. Ref-hi ,hi -ref etc. Not entirely
their fault in that the new motorcraft sensor (which is plastic) has the
connectors in a different position. Now I'm getting correct on and off
vacuum to egr . Only one possible problem . It's only 3" of vacuum. (thought it was suppose to be 5") Is that enough? I even tried a new vacuum regulator for the hell of it. I've also read that the plastic and the metal sensor (that I had) send a different vref signal to the pcm. I know you guys and girls can help. Thanks for everyones help!

 

Reset the PCM and and allow the monitors to execute before expending any more time.

 

That's what I've done. Only driven about 15miles so far so I'll wait and see. I'll try to finish a drive cycle or two and report back. No CEL at the
moment. I'll admit to a bad personality flaw in that I'm a perfectionist. The
problem is I'm not smart enough to obtain perfection on my own. That's why I spend
so much time asking questions here. Thanks for everyones help.

 

You could easily need 2-3 driving trips to adequately test this, and those trips must be at or above minimum speeds and temps for everything to cycle and work.

Dave

 

A tip on the different vacuum levels is, it depends on the throttle plate position as it affects intake manifold vacuum levels hence what the EGR sees through the regulator.

 

It didn't matter whether it was wide open or partial. Still 3". I reset the pcm and have driven about 60 miles total on 4 different excursions with no CEL return. I'm going to put another 75-100 this weekend but I believe
it's probably okay. Thanks for all the help!
P.S. I still wonder if the plastic and metal dpfe sensors are interchangeable?
I almost forgot this tidbit of info for everyones memory banks. That 12-1400 rpm
overdrive skip also went away. hum! I guess it was an air/fuel/ mixture thing?

 

It could be as simple as the pollution control warranty being so long that, to meet that time frame, the metal one is the easy way out.

Dave