I have a 2000 F150 4.6 and it started running really rough and lost most of its power. The check engine light was on and flashing.

About a month ago I had it tuned and the dealer cleaned the throttle body and replaced the Idle Control Switch(?) as well as the plugs and filters.

The light came back on last week and this time it was a P0401. I replaced the EGR valve and it helped a little but the light is still on and after the last episode there are 5 codes. The p0401 is still there and there are 4 cylinders that show a miss code.

I read the other threads and the closest to this I see is the DPFE sensor. Does this sound like a DPFE problem?

 

A P0401 is usually caused by a bad DPFE or plugged EGR ports in the intake manifold.
Since it has only been a month since it was tuned up I think I'd bring it back to your dealer and have them check it.
Do you know which cylinders the misfire codes showed up for?

 

The 2,5,7 & 8 cylinders show a miss code.

 

Replaced DPFE and it still misses badly.

 

Sounds like it's time to take it back to the dealer and tell them that since it has only been a month that they should check it out for you.

 

Maybe Racerguy or some other Ford tech can help me out. On a 4.2L which has an EGR port for each cylinder, if most plug up the entire EGR flow will go to one or two cylinders and they could misfire. On a modular engine, the EGR ports are in the intake manifold just downstream from the throttle body, so plugged EGR passages can NOT cause a misfire. Too much EGR for the RPM can misfire, too little would result in too much NOx or make pinging more likely, right?

A bad DPFE could indicate too little EGR flow and cause the PCM to command more flow. At low RPM, this could cause random cylinder misfires? But is EGR ever commanded at all at idle? But at say 1500 and above, the engine should be able to ingest any amount of EGR. Racerguy, can you tell me if I have this right?

So, if I'm right above, the DPFE could only have caused misfires at close to idle. Is this where your misfires were?

The 401 is too little EGR flow. The usual suspects are plugged passages, disconnected vacuum lines, and stuck valves. First thing I'd do is unplug the vacuum line from the EGR valve and apply vacuum with a MightyVac type pump while idling. The EGR should cause the engine to stumble or stall. If it doesn't, either your valve is already open (stuck) or the lines are plugged. You can reach up under the EGR valve on a GM valve and feel the valve opening when you pull a vacuum. Some don't.

 

Too much EGR flow can cause a misfire feel but is probably actually a lean surge.
I don't think I've ever felt a problem on a modular engine caused by plugged EGR ports.
Then again, where I live we very rarely see plugged EGR ports. Might be the type of gas we get or something.
Too little EGR flow can cause a ping because the air/fuel mixture isn't being cooled by the EGR. The PCM also might advance the timing when the EGR is flowing to help the engine run smoother and not lose power.
At idle the EGR should never open. If it did it would act like a vacuum leak. Like you said if you apply vacuum to the EGR at idle it should stumble or stall.
Even at 1500 rpm or above too much EGR can cause problems. EFI 300 I6's were sorta famous for too much EGR flow at around 1300-1500 rpm which caused a bad surge.
I think the only time I've ever felt a bad DPFE make an engine run rough is on Focuses. It seems that they are very particular about how much EGR flow they get. They surge big time with a bad DPFE while driving down the road. The PCM sees a DPFE signal that tells it that EGR isn't flowing so the PCM opens up the EGR more.

 

Thanks Racerguy, I don't have much Ford product knowlege.

 

It sounds like you do ok with the Ford knowledge

 

Problem fixed. I live in CA and one of my kids left my passenger window open during a recent storm. The water must have gone down the firewall to the top of the engine. I pulled the misfire plugs and everyone had a reservoir of water. I dried out everything, used the dielectric grease and replaced all of the plugs and now it runs like new.

Thanks Racerguy for the tips on taking out the plugs, WORKED GREAT.