1998 2.5L 5-speed 2wd Ranger XLT 175,000 miles
Bought the truck with a P1451 Evap Circuit Fault.

Here is what I've done so far:
Replace Purge Selenoid, Canister Vent Valve, ohm each part, check voltage at each part.

Next:
Ended up putting original parts back on as they tested good and do work.
Voltage at purge is 12.5V
Voltage at Canister Vent Valve (under bed about spare tire) was .4-.5V

So I know the problem is either a wire of the control module (PCM/ECU/ECM...everyone calls it something different)

I checked voltage about 2 feet from the Vent Valve plug and it read the same. I know the most common fault would be by the rear driver shock area. Thinking at this point the computer is at fault.

Any addition thoughts or ides? Please reply.

 

Tried the new computer and didn't fix the issue.
Going to recheck wires and connections.

 

On later models, 2000/2001, there was a problem with the "thru body" connector, with this and similar codes.

So unplug any connectors you find and check for water intrusion or similar issues.

And just as a heads up, EVAP codes are very hard to clear, they can not be "reset" like other codes, they just pop back up usually, I think Ford dealer's advanced scanner can do it but not a simple procedure.

Computer(PCM) has to self clear by testing EVAP system over a few drive cycles, up to 10, one drive cycle is engine heating up to operating temp(190degF) and then cooling down below 130degF.
It is recommended to keep fuel level above 1/4 tank and below 3/4 tank during this time for quickest reset.

 

Found and fixed the issue.
Turns out the loom wore through and 3 wires were gone from arcing and corrosion right after the rear harness plug by the fuel filter. It was right in front of me and I didn't notice it before.

 

Good work and thanks for the update

Wiring issues are very very hard to find