Still trying to figure out my "check engine soon" light. It appears solenoid, EGR valve, and DPFE sensor are operational. Still getting code 401 EGR flow insufficient. I put vacuum gauge on EGR line and after 15 minutes of running the needle still registered 0 Hg of vacuum. Shouldn't I be seeing some vacuum action? And how much vacuum should be measured if functioning properly? Also, have been trying to test MAF sensor. Does anyone have a Ford book showing which is the signal wire from the MAF? My books show a round connector, but on my '99 F-250 there is a flat four-prong plug. The red is voltage, the black is ground, but the tan and blue I don't know. Appreciate any help. Thanks

 

The egr valve does not open at idle witch is why your seeing no vacuum. With the code you are getting maybe the egr passages are cloged.

 

I've pulled the EGR valve off and everything looked to be in good shape. There was a slight layer of carbon that would come off on your finger but no indication of any significant buildup or blockage. When checking for vacuum I placed the truck in gear and let in run - is that still not enough to get a measure of vacuum?

 

it looks like tan is signal & blue is signal common (not chassis). that doesn't sound like the trouble though. you might try a "t" in the egr vacum line and take the vacum gauge in the cab with the actuator hooked up. I think you have to be at cruise speed to actuate the egr.

 

Redlariat - thanks for the info. The reason I ask is that my Haynes manual claims to test for a bad MAF, if the MAF Sig (+) and the Gnd (-) show open circuit - then the element could be damaged. And my understanding is that PCM activates the EGR system based on information gathered from the ECT, TPS, and the MAF along with other factors. Since components of EGR appear(?) to be functioning okay, I figured I would start looking at the things that might affect the signal from PCM to the EGR system. Right now I do show an open circuit on the second and third terminals on the MAF sensor which would connect to the ground (black) wire and and the tan wire which you say might be the signal wire. Based on the manual, that would suggest a bad MAF sensor, which might prevent the PCM from activating the EGR. I think I'll try your idea - I just need to find a place to run a line through the firewall. Thanks for your help. Let me know if you can verify the tan/MAF signal connection.

 

the tan is drawn in the chiltons as a slider in a potentiometer. I don't believe there is actually a physical connection as the MAF measures the current change to maintain a set temperature so it is probably electronic. the diagram shows a hard connection of red to blue through one hot wire & one end of the other hot wire hooked to the blue junction with black on the other end. the tan is variable but I'm not sure how. try a meter on the tan and blue cause they both go to the PCM.

 

I've got what I need to tee off on the EGR line and I'll try to measure the vacuum on the fly tomorrow. Interestingly, I cleared the code on Tuesday evening and I have not had any codes show since then. I usually got the codes back the same day or the next day. We shall see. Thanks for the input.

 

I think I will post again. But this morning I got a code after driving for only 4-5 minutes and when I read it, it was a 402 which is now EGR flow excessive (actually second time in a row)! Before the codes have all been insufficient. Could it be the EGR is getting hung up? I hadn't got a 402 code before I put the 10 Hg of vacuum on the EGR a few days ago. Is it possible the EGR wasn't opening at first and since I pulled the vacuum on the EGR it is now in a stuck-open position causing excessive flow?

 

sounds like your DPFE sensor is junk.

 

That's what I had originally suspected, but I checked the ref voltage which was running about 5 volts. Also, checked voltage as engine warmed and it gradually worked it's way up to about 3.9 or 4 volts before I quit measuring. This seemed to conform to information in the Haynes manual. Any other way to check it? Could the EGR be sticking?

 

Nomopar and others: - I had run a voltage check on the DPFE sensor about a week ago and it seemed to match the specs in Haynes manual. With key on the signal read about .7 volts and with engine on it slowly rose til it peaked about 3.9 which is a tad low. At the time I was getting insufficient flow codes. The last few days I started to get excessive flow codes. Upon reading your post I decided to retest the DPFE sensor. Again, it read around 1 volt with the key on but within 5 seconds or so it started going crazy with big fluctuations in voltage. It finally settled in at about 3 volts which is too high. So I spent the $84 and put in a new sensor. I haven't driven it much yet so I don't know if that will take care of my problem. I will keep you informed. I will say - though, I checked the new sensor and it is reading 1 volt which is a little high based on Haynes. After letting it run for a few minutes, I did not see any change in the voltage. So, had I been checking this new sensor, I would almost expect it to be defective as well. The manual I have is for '97 -2000 Ford trucks. Is the information accurate in these manuals or would specs for the EGR change from year to year? I will say the truck runs smoother and I'm not getting the stumble at 1500 rpms like I had noticed before. I appreciate your input - you guys work on these things everyday and you've got the experience that we don't.

 

Well, it's been three days since I changed out the DPFE sensor and no "check engine soon" light! I think the problem is fixed. Just today I spoke with someone who has taken their vehicle to the dealer twice only to spend big $$$ and to have the light come back on a few days later. Couldn't have solved this problem without the code scanner and help from you guys on this site. Thanks.

 

I am having a pinging problem and had a question about testing the DPFE sensor. My DPFE is reading .6 volts when cold. To test the "warm" output, do I leave the engine at idle or am I supposed to drive around and watch the ouput as the EGR turns on and off?

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1998 F-150 XLT, Ext Cab, 4.6/auto, 3.55 R, FlowMaster 40 Series w/ dual 3" chrome tips, CraneCams 8.5mm FireWire spark plug wires

 

Thanks for the responses. I don't have any codes and I recently took off the upper intake and while I had it apart, I cleaned out the EGR passages that go from the EGR valve into the intake. The passages were pretty well clogged with pasty oil/carbon mess.

Even after cleaning it out, I still get the pinging.

I know the EGR shouldn't operate at idle and WOT, but should it operate over 1/2 throttle or when the engine is under a load? Those are the situations where I get pinging. I recently hooked up my voltmeter to the EVR valve and watched the amount of voltage it received while driving around. It only received voltage above idle and just under 1/2 throttle. Under load and above 1/2 there was no voltage, therefore no vacuum going to the EGR valve.

I've also run a few cans of Techron cleaner through the system as well.

Thanks for the help.

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1998 F-150 XLT, Ext Cab, 4.6/auto, 3.55 R, FlowMaster 40 Series w/ dual 3" chrome tips, CraneCams 8.5mm FireWire spark plug wires

 

Replace the DPFE sensor. A faulty Maf will not set an EGR code. The 401 code is insufficient flow, not "too much or too little flow". It is hard to test this since the voltage can be off a few 10ths and set this code. THe only other thing it could be is partially plugged egr passages in the intake. These DPFE's are faulty all of the time.