Failed Emission Test (EGR)

[Wordwoman]

Much to our surprise, we recently failed the emission test on our 1997 Ford Explorer. Failure reason: The malfunction indicator light was commanded on Code PO401/EGR Flow Insufficient. (No check engine light had been showing.)

Because we couldn't detect a vacuum on the EGR, we replaced the EGR solenoid. Upon further investigation we found out that no vacuum would be present while revving the engine in the driveway. While driving it with a vacuum hose and gauge attached to the EGR valve, we got a fluctuating reading from 0 - 5. We put a vacuum hose on the EGR valve and sucked on the hose while the engine was running which made the engine almost stall indicating to us that the valve was opening.

Now what? Any suggestions on what might be wrong that would cause me to fail the emission test for insufficient egr flow??

Thank you for any help you might be able to give me. We only have until Saturday when the State of IL suspends both our licenses for failure to pass the emission test!

 

[Robb]

Your DPFE has gone bad.

Follow the two vacuum hoses from the EGR tube to a little box with an electrical connector on it. That is your DPFE, and it senses flow through a metering orifice in the EGR tube.

 

[Wordwoman]

Wouldn't a bad DPFE give me a check engine light?

 

[Robb]

Yea, most of the time, it should if it is bad enough. I am not an expert on the subject, but I will throw out what I know. The DPFE would be the sensor which would tell the Emission Test instrument that flow was actually low, and the DPFE is notorious for going bad on Explorer 4.0s. It is an extremely common problem. If you have tested the EGR Valve, there isn't much else in the system that could be wrong, except for a physical blockage. Blockages are common on some other engines (4.6Ls in particular), but I haven't read about them being a problem on the 4.0 or 5.0.

 

[Wordwoman]

Yea, most of the time, it should if it is bad enough. I am not an expert on the subject, but I will throw out what I know. The DPFE would be the sensor which would tell the Emission Test instrument that flow was actually low, and the DPFE is notorious for going bad on Explorer 4.0s. It is an extremely common problem. If you have tested the EGR Valve, there isn't much else in the system that could be wrong, except for a physical blockage. Blockages are common on some other engines (4.6Ls in particular), but I haven't read about them being a problem on the 4.0 or 5.0.

Thanks for your help, Robb! You were right. The DPFE was probably the culprit. Turns out the check engine light was not working and had to be replaced. No wonder we had no clue something was wrong. We passed the emission test last week. Of course the moment we passed, the headlights stopped working. Back to the drawing board to try to figure this new problem out. Fuses are fine. Turning on the high beams woke the headlights up for a few days, but now they seem to be soundly sleeping forever.

 

['96explorereddiebauer]

...Of course the moment we passed, the headlights stopped working. Back to the drawing board to try to figure this new problem out. Fuses are fine. Turning on the high beams woke the headlights up for a few days, but now they seem to be soundly sleeping forever.

It could be your multifunction switch. Either that or both of your headlights blew. Heh...it happened to Davo(Digger196) before while driving at night. It was pretty funny!!