I have a 02 Expedition with the 4.6. It shows the egr code P0401 and I have replaced the egr valve, control valve, and circulation sensor. The last time I took it off I blew air down the exhaust tube with the circulation sensor off, but nothing has changed. I have checked the vacuum lines and everything seems to be ok. Please let me know what you think.

 

Pull the vacuum line off the EGR valve and connect the port to a suitable vacuum source; start the engine and let it idle, then pull ~10 inch vacuum on the EGR valve to open it and see if the engine begins to stumble.

If with the vacuum applied the engine idle remains smooth, then the EGR passages in the intake gooseneck are clogged.

If the engine stumbles, but the error code persists, then something is awry in the electronics or electrical system. Try disconnecting the battery negative terminal for a few seconds to reset the PCM. Sometimes that will correct an error code situation. Also, check the vacuum source between the EGR vacuum control valve and the manifold. If no vacuum is there, the line is either broken, kinked or disconnected.

 

I went home last night and tried that. I pulled the vacuum line off of the fuel rail and put it on the egr valve since it seemed to have quite a bit more vacuum than the one that was originally on the egr valve. It did run a little rough idling but it was just like it had a mild cam in it.

 

I think the ports are severely restricted. The engine should flat *** stall with EGR on at idle.

 

Thanks for the info Bill. I will go home tonight and try to take the throttle body off and see if I can clean it up any. I will let you know what happens.

 

I cranked up my 4.6L, let it warm up a bit to bring the idle down, AC off, and connected up my vacuum pump to the EGR valve port.
If the vacuum is applied quickly, the engine will almost stall, but the PCM discovers the anomaly quickly and adjusts the IAC to compensate. The idle is rough, but it doesn't stall.
If the vacuum is applied slowly, then the idle is just rough.

FYI: I have recently overhauled the EGR system including cleaning out the passages in the intake gooseneck, so max flow through the EGR valve is attained with the vacuum pump.

 

Well I have thank everyone for the information. I took the spacer off between the throttle body and the intake and sure enough the egr ports were completely filled with carbon. I got it all cleaned out and it runs like brand new again. Thanks to all of you.