Hi guys, I have a 96 f250 5.8 and I just scanned my codes and got 334 which I found isPFE or EVP circuit above the closed limit of 0.67 volts, I just replaced the EVP not long ago so does the DPFE need replaced or could it be something else?

Also, I get 172, which is:HEGO sensor circuit indicates system lean (right side) this is a stupid question but where is this oxygen sensor, I glanced around and didnt see anything. My truck is the OBD1 version. Thanks

 

the o2 sensor is in the exhaust pipe on pass side next to tranny.

 

Your truck has either an EVP sensor or DPFE, not both. 334 indicates the the voltage is too high when the EGR is supposed to be closed. Most common cause is carbon build up in the EGR valve itself. Take it off, inspect, clean, reassemble. You can use a DVM to probe the signal output to verify if your cleaning was successful. Be sure to clear the codes after you you do any repairs.

Your DTC 172 can be caused by leaks in the exhaust, bad vacuum lines or a stuck open EGR valve.