Hello all,
I have a 2002 Mountaineer (Explorer) with the 4.6 V8. 66,000 miles.
Truck started running strange at 35-45 mph like it was hunting for gears. A couple of days later, service engine light came on. I pulled up code PO401 EGR insufficient flow.
I removed and cleaned egr valve and tube and replaced gasket. I then connected egr valve to my vacuum pump. It opened and held vacuum. I then did this same test this time with engine running at idle. Engine quickly shut off as it should when I applied vacuum.
Ran fine and no engine light for one day. Then the engine stumbling returned and service engine light came back on.
Since the EGR valve seemed to test ok, I replaced the egr pressure sensor and reset code.
Same result, engine ran fine for two days then the stumbling returned and service engine light came on again. This time, I replaced the egr vacuum solenoid. Once again, same result truck ran well for two days, then stumbling returned and light back on.
I am now at a loss for what could be causing the problem. I normally am not the kind of Tech that likes to throw parts at an engine and hope for a resolution to the problem, however that is what I feel I have been doing here to no avail. Since the egr valve seems to have tested ok, I am reluctant to replace it. Does any one have any idea what may be going on or have you ever seen this problem before?
Thanks in advance for your help.
Paul

 

A bad DPFE sensor is the most common cause for a P0401 code. These get corrosive moisture in them from the exhaust and then fail.

 

Thanks for the advice but I have already replaced the DPFE sensor. Problem still persists. In fact I now have a code P1401. I got the replacement DPFE at AutoZone. I am beginning to think it is also bad. Wouldn't be the first time I got bad parts at autozone.