1997 F 150 4.2 2wd with 206k Km's
Okay, so I've been doing alot of reading on here lately about this problem. I've had the CEL on basically since I got the truck (around 1 year). So tonight I went out and did some testing.
1. Checked EGR valve. Applied 5-6 in/hg with engine at idle. Rpm's dropped considerably.

2. Checked DPFE sensor using guidelines in haynes manual. Referance voltage: 5 volts. Voltage when hot: 5 volts. I wasn't able to check when cold.

3. Checked EVR using guidelines in haynes manual. Check for battery voltage: 12 volts. Resistance: 33.7 ohms.

So since the engine bogged down when I applied vacuum to the EGR valve the EGR valve is working and the ports are clear right (based on what I've been reading)? And since the EVR appears to be working that leaves the DPFE sensor, but it appears to be working too. I'm not too sure of whats going on, but I'm willing to bet the DPFE is at fault.Any ideas? Should I check the DPFE when the engine is cold to make sure?

This truck needs to pass emissions testing in less than two weeks, so any help or advice will be greatly appreciated.
TIA

 

Is the DPFE the original pot metal unit or has it been replaced with a black plastic one? The DPFE is always suspect when you get the 0401 code, especially if you have the original sensor still on it. Also was the light on when you bought the truck or did it come on shortly after? I say, look at the cheap easy fixes first. Remove the throttle body and spacer and clean the ports whether they need it or not. 10 bucks for gaskets if you need them and a can of TB cleaner and then you know for sure they're clean. While you've got everything apart look at the EGR and make sure its not stuck open. The EVR hardly ever goes bad; leave it alone for now. If everything checks out to this point, look at the two hoses that connect the EGR riser to the DPFE sensor. If they're good then go TO THE DEALERSHIP (or an online equivalent) and get a new DPFE. If that don't fix it make sure you tell us what does.

 

when i tested my egr it made the engine bog down, but when i checked my ports out they were about 75% clogged. i also tested my sensor and the voltages seemed fine too. but running out of options i replaced it with an aftermarket one to no avail. finally replaced it with the 75$ ford sensor and the light hasnt been back .

 

You can't test a DPFE with a simple test a Haynes tell you to do.
It is a sensor with electronics inside that has to respond to changes in pressure.
A voltage test will not do it.

 

Sure you can. All you need to do is apply vacuum while measuring the output. There is a very proportional relationship between the vacuum applied and the output voltage of the sensor.

I'd suggest that you clean the intake ports thouroughly and replace the DPFE sensor with a Ford unit, not an after market unit.

Steve

 

This I know, but most people won't test in this manner without equipment and test info.
A static voltage test is of little value for anyhting but it's there , low or missing.

 

Get yourself an IDS. Perform a KOER test and measure vacuum output to the EGR during the test. If it pulls a vacuum, test the EGR by pulling a vacuum. If it tries to stall the engine, replace the DPFE.....

 

Ok thanks for all the help guys.
I think I forgot something that might be helpfull when I did the original post. About a week before I tested it, I had cleared the code to see what would happen and I didn't touch a thing. Then around a week later it came back on. This is when I tested it. After testing it and everything looking good (or so it seemed). I cleared the code again to see what would happen. It has stayed off since then.

Also, it was booked for an emmisions test today. So instead of rebooking it so I could play around with it some more, I just took it in. The garage where I took it has a "don't pass, don't pay" thing going on, so no big deal if it fails. Guess what? Passed with flying colours. Now I'm really confused. Why would the CEL be on if the emissions were perfectly normal? Hmmm maybe it is the DPFE? If the CEL comes on again I think that's gonna be the first thing to be replaced.

Oh yea, the sensor that is currently on it is the silver coloured metal one. And I think the CEL came on a little while after I got it (1-2 months at most).

Again, thanks for the responses guys.

 

The metal sensor is probably the original sensor that came on the truck. I wouldn't doubt that it's gone bad. Glad you passed the sniffer test, though.