Ok Guys need help!
98 F150 4.6 EGR loses ported vacuum signal. Trucks pings randomly and occasionally throws a EGR low flow code. Have inspected the entire EGR system and finally frustrated tee'd the EGR vacuum line and ran a gauge into the cab. No EGR vacuum until the truck warms up (normal). Once warm EGR vacuum modulates with load and pedal (normal). With no movement in pedal or change in load vacuum goes to zero and never moves again (not normal). Shut off truck and re-start and vacuum returns from anywhere from 1 min to 20 miles, depending on the trucks mood. Although I have never had the vaccum gauge on in the past I will never throw a code until it gets above 20 degrees, but when it's cold the EGR works fine (no pinging).
Thought or ideas? More details? Thanks in advance.

 

Post the DTC.

 

Good question- Guess since I have run the tests I have eliminated things that may be relavent to the cause. Code P0401 is displayed when the CEL comes on. If you are in IM mode it throws a pending P0401 shortly after the ported vacuum signal is lost. I have inspect the EGR valve and tested it. I have replaced the DPFE and vacuum solinoid. I know the EGR tube could be a potential issue as well as the ports in the throttle body and thinkng it may be slightly restricted but when you apply vacuum to the EGR the engine does stumble bad and then improves slightly. Using a manometer to the the differential pressure of the EGR tube the reference side goes into a vacuum if the EGR valve is held open. This tells me the ports are not sealed or it would maintain a posivtive pressure. KEY NOTE- the code is only thrown after the vacuum is lost. I was maybe leaning to a bad MAF temp sensor but have no way to test it. As I stated when its 20 or below it works fine. The warmer it gets outside the quicker it throws a code. I really do not know what drives the EGR function as far as temperature or additional components. If anyone has a link to the logic schematic I would appreciate it.
Hope this helps.

 

Clean throttle body, replace DPFE.

 

Ok I found the info I was looking for. Thanks for your input as I stated in the thread I have replaced the DPFE and I suspected a restricted EGR tube. Below is what I needed to know and hopefully it helps someone else. As I stated the problem does not show up when it's cold.

"Note: EGR normally has large amounts of water vapor that are the result of the engine combustion process. During cold ambient temperatures, under some circumstances, water vapor can freeze in the DPFE sensor, hoses, as well as other components in the EGR system. In order to prevent MIL illumination for temporary freezing, the following logic is used:

If an EGR system malfunction is detected above 32 oF, the EGR system and the EGR monitor is disabled for the current driving cycle. A DTC is stored and the MIL is illuminated if the malfunction has been detected on two consecutive driving cycles.

If an EGR system malfunction is detected below 32 oF, only the EGR system is disabled for the current driving cycle. A DTC is not stored and the I/M readiness status for the EGR monitor will not change. The EGR monitor, however, will continue to operate. If the EGR monitor determined that the malfunction is no longer present (i.e., the ice melts), the EGR system will be enabled and normal system operation will be restored."

 

Water vapor is normal and has no effect on the system by design, (ie heavy hose insulation) should NEVER ice up. This is abnormal conditions if true. Trucks sold under these conditions do not have such EGR systems (the sub- zero's -60 and below) Vehicle must have been imported and you must live @ the north pole for this does not occur normally. What happens is the EGR port clogs thru PCV system from short trips in cold climate situations.

If you asked instead of dictated, you would have found your answer much sooner. The tubes don't plug 2 the orifice either. Should have checked your port in the elbow, you should have suck tested the valve operation to determine.

Better luck next time

 

jbrew-
Obviously you have not understood my thread. I respect your senior member status and I am sure you are far ahead of me in Ford technology. But I did not dictate, only requested the PCM logic which I have displayed in the thread.

North or South pole the logic exists (I never implied that it was freezing up)which was causing the ported vacuum loss based on ambient temperature and EGR shut down logic. I agree your diagnosis was correct (blocked EGR)except for the DPFE, but re-read my question. What is the PCM logic?

I will not clutter your forum again, but thank you regardless.

 

When you vacuum tested the EGR valve, did you use a Gauge to see if it was holding The vacuum? If the engine stumbled then regained its idle capacity, I would think the diaphragm in the valve was leaking, or you had a leak in your test equipment. The EGR should hold the vacuum you applied to it until you release it.

 

If you have never cleaned the EGR tube into the intake, then it needs it bad. Cleaning that is your cheapest possible solution. I should have done the cleaning before I replaced the DPFE sensor. No codes now for nine months.

 

Right , that's the very first thing you do with a 401/402 (poppet). That simple little test will point you in the right direction lol. - Man, - toddgast, you where seriously over thinking it lol.

No matter the matter, - if your still around, post up! I'll link you to a great site where you can get a crash coarse on this system. Other monitors as well, but I'll link you the EGR. I'll post yuh a , write-up I have done on the EGR system as-well. - If your still around and didn't head for the hills already

 

Over think, yea that's me. The older I get I need more information to satisfy me! Thanks for the email reply.
EGR valve held fine, did not post that since it passed. Throttle body was PLUGGED, cleaned it and now we will see when it warms back up (if that happens). Still pings at over 2200 rpm and vacuum does not shut down (been too cold)., With that said I think the orifice in the tube may be restricted but the pinging is gone under 2200 rpm so it appears the cleaning did help. Once it warms back up I will let you know the status. As I said before, it does not throw a code until it warms up outside, but throttle body was plugged bad.
The part that was really confussing me was that I could drive a week with no code and then the next time drive to the store and have a code and one pending. Now that I understand that logic your recomendations still hold true. Yea, overthink (but sometimes it does help to eliminate the obvious).