I have a '99 XL with the 4.2L. It has about 96K miles on it.

After getting a new CEL, I took my truck into the dealership, and they replaced the DPFE sensor and reset the PCM.

I'd never heard of the DPFE sensor before now, but I could swear the truck is a lot peppier now. I have no idea what this part does, but is this apparent performance improvement real or just in my mind?

 

Well I can tell you the DPFE sensor is the differential pressure feedback EGR sensor. Essentially it controls the EGR valve. I just changed the one on my 01 4.6 along with a good cleaning of the nasty EGR ports in the throttle body. I picked up a little pep and some mileage after all of that too. I guess we will have to wait for an expert to chime in for a hard reason why or why not you should or should not see any performance difference.

hope that helps,

 

This sensor operation is done in the cruise range only.
It allows exhaust gas to be introduced into the intake air stream.
Notmally doing this reduces power so if there was a fault letting exhaust flow at any other time, then performace will suffer.
To go on, the ignition timing is changed and the fuel is cut back when the operation is called up by the computer.
This is done for two reasons. Exhaust in the intake air requires less fuel and can use advanced ignition timing.
The results of this is an increase in fuel mileage as well as a reduction in the engine output of Nitrogen Oxide emmissions by cooling combustion during this operation.