This 2001 Ford Expedition came in and the customer requested that the EGR valve be changed. I asked why and was told the parts store checked it and it had a code P0401 for insufficient EGR flow. I said okay, but I was willing to bet that the EGR valve was okay. The customer asked why I was so sure and I informed him that I have repaired a code P0401 in many different Ford vehicles, hundreds of times and I have never changed an EGR valve to fix this code. I am not saying that the EGR valves cannot fail but I personally have not seen it be the cause of an insufficient egr flow code. I told him it would take about five minutes to test the valve. First I went and got my hand vacuum pump, as pictured below.
I located the ERG valve on the driver’s side of the engine.
I disconnected the vacuum hose.
With the engine idling I hooked up my hand vacuum pump and applied about 25″ of vacuum to the EGR valve. The engine idle surged down almost to a stall condition and then recovered and ran a little rough. The valve held vacuum and the engine almost stalled so the valve is good and the passages are open. We need to look for something else and not waste money on replacing a good EGR valve.
If the valve would not have held vacuum the valve would have been faulty. If it would have held a vacuum and the idle speed changed very little or not at all, the valve would most likely have been okay and the egr passages would have been blocked with carbon build up. Another thing to keep in mind is that if no change in engine rpm is noted, the engine should be turned off and then apply vacuum to the EGR valve again. Movement of the pintle and the diaphragm should be heard and felt, while applying vacuum and during quick release of the applied vacuum. . If vacuum is held and no movement is detected the EGR valve itself may be stuck. The customer paid the bill and said he would be back but I have not seen him yet. This one or another one will come in soon and I will document what really is the problem.