Starting fluid is ether, it would ignite with out much compression, gasoline won't, it needs at least 100psi.
Ford 4.0l SOHC(2001 and up) is an interference engine
Ford 4.0l OHV(1990-2000) is non-interference
Your coil pack ohms out correctly and it has correct voltage so problem is either Computer(PCM) or wiring from computer to coil pack.
The fact you get any spark means CKP sensor is working.
The 3 coil pack wires run to the PCM, the ICM(ignition control module) is in the PCM on an '04.
Coil packs work the same as the old distributor setups with points did.
Coil gets 12volts when key is on, then to spark the coil it is grounded and then ground is cut, this cutting of the ground sends out a spark, points grounded(closed) and cut the ground(opened) to the coil.
On electronic ignitions transistors(switches) are used instead of points.
The PCM uses an external ground to charge up(ground) each of the 3 coils.
The PCM has several grounds that are not shared internally, so it could just be a bad ground wire for the ICM.
Can't remember when Ford moved the Ranger PCM to the upper firewall(near the center) but there was a problem with the connector getting moisture inside, they added a cover on later years.
Maybe your PCM connector has some corrosion inside.
I would rent or borrow a compression gauge, just to take compression off the table.
The big three, spark, fuel and compression are it as far as a no start.
You gave it fuel and no luck
So all that is left is spark and compression, compression is easiest to check and is a black or white result, you need average 150psi, all spark plugs removed and assuming battery is turning engine over at a good speed.
4.0l SOHC should run at about 170psi though.
I think people sometimes get caught up in the electronics on newer engines and skip over the basics.
Spark, fuel, compression.
For a sensor or computer to cause a no start it has to effect either spark or fuel, it can't effect compression.
fuel is easy to test, dump some in and crank, lol.
compression is also easy to check, and either you got some or you don't
spark is where the electronics can require volt and ohm meters