I have a 2004 Ford Ranger 4X4 4.0 and have been looking online for replacement PCM's . Any suggestions
for a reliable source or manufacturer?

 

Welcome to the forum

No suggestions as to reliable source

But a few heads up
2004 Ranger will have PATS(passive anti-theft system), this means the current keys have an RFID tag in the handle, and current PCM will have those key's tag numbers in memory.
When you turn on the key the computer reads the tag number and checks it against numbers in memory, if there is a match then fuel pump and injectors will work, if no match then no fuel pump and no injectors, so no start.
Starter motor can also be disabled if no match.

So new PCM should come with new Blank Keys that can be cut to match your ignition/doors, and these new key's RFID tag numbers should be in new computers memory.
Old keys would no longer work, although you can add them to the new computer if you have 2 working PATS keys, easy to do.

Ford PCM part numbers
4L5A-12A650-BCA <<< example PCM part number

4L = 2004, 3L = 2003, 5L = 2005
5A = Ranger electronics

12A650 = Ford's generic part number for ALL PCMs, since around 1984 Ford has used 12A650 and still uses it in 2018

BCA = firmware and revisions, Ford doesn't publish a decoder for these numbers
Often denotes manual or automatic trans


PCM doesn't effect Keyless entry, that is done by RAP module, so new PCM and new keys wouldn't effect that