Naked DPFE with Pictures!

[95ExpLim]

This is the third time I've replaced the DPFE in my '95.

I couldn't find this information for the '95 (may apply to other years...) all in one thread so trying to help others with this common problem here goes...

The DPFE failing causes a very light to mild surging while the vehicle is more or less at a constant speed with light throttle. The CEL will be on the majority of the time, if it goes out it will be for a brief time. I think my in-town MPG dropped about 2 MPG also, to 16.

I don't have a scanner so I grounded the "STI" plug under the hood and started counting CEL flashes. My '95 is OBD or OBD1, which ever, and presented the following codes:

327----PFE sensor circuit voltage below self-test minimum

337----PFE sensor circuit voltage above self-test maximum

Both KOEO (on demand fault code) and KOER (continuous memory) gave these two codes.

I can see continuous memory having a record of exceeding both the min and the max but seems "on demand" would be limited to one or the other.

Replacing the DPFE reset the codes on the next start but haven't driven it enough to see if there is an improvement in the MPG.

The DPFE was about $53 at Autozone and took a couple of minutes to replace. Two 7mm screws IIRC. Two vacuum lines.

The NAKED DPFE!

The exhaust sample does not flow through this sensor. The port on the DPFE where the exhaust sample pressure is measured was almost bright metal. No gunk or carbon at all.

 

[wickedrigs]

Can the DPFE be "dummied" and/or removed for mileage and power gains?

 

[IZwack]

That just refers back to the question of the EGR system - in general, removing the EGR should either have no noticeable effect on MPG, or decrease MPG (due to the oxygen volume increase per cylinder). However, it should not improve MPG unless the EGR system was faulty from the beginning.

 

[wickedrigs]

I understand that the EGR helps with pollution, but also know that when they are bad they promote pollution by decreasing fuel economy. When removed on a diesel truck they help out immensely and thought it would be the same on the 4.0L motors. This may not be the case. Also, with this unit removed it would be one less thing to have go wrong.

 

[2000StreetRod]

EGR advantage

One advantage of a functional EGR system is reduction of combustion temperatures. The result is longer lasting valves.

 

[95ExpLim]

DPFE problem update...

After running the new (Autozone) DPFE I'm still getting an intermittent CEL.

I pulled the electrical connector at the DPFE and measured the reference voltage, was 5.02 volts, all three pins on both sides look bright and clean. Can't get much better than that.

I pulled both hoses off at both ends (seems like they are silicone) and they were in great shape -no plugs either. The larger hose was stuck on the exhaust "Tee" and had to cut it off. It's just long enough to make connections now.

I put 80 psi air into both tees thinking the restriction in the pipe between the two tees might be plugged.

Hooked everything back up and a few miles later had the CEL again. At this point I'm going to buy a FORD DPFE and if I still get the CEL I'll put a bit of black electrical tape over the light.

 

[2000StreetRod]

Check the EGR valve and EVR

This is the third time I've replaced the DPFE in my '95. . . My '95 is OBD or OBD1, which ever, and presented the following codes:

327----PFE sensor circuit voltage below self-test minimum

337----PFE sensor circuit voltage above self-test maximum

. . .

The PCM reads the PFE sensor voltage when the EGR valve should be closed and open. Your EGR valve may have failed. I suggest that you test it and the EGR vacuum regulator before buying another PFE sensor. See the following thread: EGR System O&T

 

[95ExpLim]

The PCM reads the PFE sensor voltage when the EGR valve should be closed and open. Your EGR valve may have failed. I suggest that you test it and the EGR vacuum regulator before buying another PFE sensor. See the following thread: EGR System O&T

Great thread 2000StreetRod!

My Ex is OBD, June of '95, is the PFE voltages different from your '99?

I applied 5in/Hg to the EGR and it held it fine for 5 min. I could hear the valve "thunk" when the vacuum was released also.

With the hand vacuum pump hooked to the EGR and the engine idling applying approx 2in/Hg would cause the engine to almost stall.

I have the aluminum type PFE and back probing the plug (brn/lt grn to gray/red) with KOEO gives a voltage reading of .003 volts. The 5 volt reference (brn/wht to gray/red) reads 5.02 volts KOEO.

I monitored the PFE voltage while driving (dvm back probing PFE plug) and never saw the PFE output of .003 volts change. Zero to 60, overrun down to 30 and steady load at 50 mph cruse.

Until I can determine what the proper voltage the PFE should be sending to the PCM with KOEO I'm stalled in the trouble shooting...

 

[2000StreetRod]

PFE sensor voltages

The PFE sensor voltages should only be slightly different than the DPFE voltages. Your PFE sensor is not reporting an open EGR valve. Since you know from the hand vacuum test that your EGR valve opens and the EGR path is not blocked, the problem could be either a bad EGR vacuum regulator (EVR) or a bad PFE sensor.

I suggest that you test the EVR as described in post #4.

 

[GRNMACHINE]

Great writeup 95-Subscribing-interested in hearing the outcome.