Code 335 (KOEO) -- DPFE volts out of range -- Why do I care? :)

[barrys]

Just thought I'd ask...
It's a 1994 Ranger V6 3.0 with auto trans.
I had a lame smog result -- passed but not with flying colors -- high HC and medium high NO.

I read up and did the KOEO and KOER tests and got these results consistently and repeatedly:
335 (KOEO) EGR sensor circuit voltage higher or lower than expected during self-test
336 (KOER) EGR sensor circuit voltage higher than expected
336 (KOER) (Trucks ONLY): Exhaust pressure high
I got those code defs from the Equuis scan tool manual.
Not sure which 336 definition I should go with.

The truck is running fine, idles fine, and no other codes were thrown from either test repeatedly. In one test, I _think_ I saw a 328 -- EGR closed voltage lower than expected, but I could not get that to repeat.
But, I'm not sure and never saw that again.

Then, I read up some more and did a voltage check on DPFE and saw (KOEO):
VREF: 5.0V
DPFE: 1.29V
Started with cold idling engine:
DPFE: 1.86V
Based on reading, the DPFE is most likely to fail out of all the EGR components and those voltage tests show a failing DPFE.

So, replacing it seems straightforward enough. But, what is actually happening when the car runs with the DPFE functioning like this? Is it a real problem with how the engine runs or strictly an emissions problem. I'm not one who likes to pollute, so I'll try to fix this no matter what. But, you guys are so ontop of this stuff, and I would enjoy a little more education.

The last time I worked on cars, I could not even spell EGR which was OK since that car had like one vacuum tube and the exhuast went right out the tailpipe...

 

[barrys]

Oh yeah... No check engine light, no saved codes.

 

[Wicked_Sludge]

the DPFE sensor itself is probably failing. thats the usual cause of codes like this.

the EGR systems sole purpous is to reduce emissions, obviously. but like many emissions systems on your vehicle, if it isnt operating properly, it can effect drivability, power, and fuel economy. the DPFE sensor is there to relay information on exhaust backpressure, and EGR system pressure to the computer so the PCM knows how far to open the EGR valve, and how far the valve actually opens. if the DPFE sensor is malfunctioning, it will send false readings to the PCM which will in turn operate the EGR based on these false readings...thus you get too much or too little EGR flow at the wrong times.

not that any of that really answers your question...so heres the short version: an EGR system that is not functioning properly can lead to decreased fuel economy, decreased power, spark knock/detonation, increased emissions, and rough idle or stalling.

 

[betomonroy]

In other words... Change the DPFE sensor.

 

[barrys]

I tested, I ordered, I replaced, I retested...
Just FYI for anyone else who's looking at this:
The DPFE design changed along with it's connector (go figure with all these failures I read about) and the new one came as a "kit" with a new mating connector, crimps, shrink tubing, instructions, and everything.

I hear about people picking up used ones with the original design from junkyards to avoid dealing with the new connector. But, with the kit from Ford, why bother with something that's likely to fail or may have failed already.
Took just about 15 minutes to install. No codes after that.

Also, I got it online at "Tousley Ford Parts Depot." They're freakin awesome. It's a dealer so they know everything and got me the exact right part at something like 1/2 of what my local dealer wanted. Ask for "SVT Steve."

 

[351crownvic]

The computer stays in a open loop ( i can never remember if its a closed or open loop)... either way when the emisions system malfunctions the computer doesnt accept input from o2 sensors or egr valve... thus resulting in lousy mpg's and low engine power..