1994 Ranger 4.0l uses Batch Fire injection, 3 injectors open at the same time, and are alternated with the other 3 every 1 RPM, usually odd/even, so injectors 1 3 5 open then 2 4 6 open on the next rotation of crank shaft
This is very close to how a carburetor works, lol, so not very efficient
The intake is just kept full of air/fuel mix and when an intake valve opens if sucks in what it needs, same as a carb setup
What happens is the the fuel coats the inside of the intake so is wasted
Sequential injection opens each injector as its cylinder's intake valve opens, so less wasted fuel coating the intake
While this can be done with just a Crank sensor, the addition of a Cam sensor makes it more precise
1994 Calif sold Rangers or Explorer 4.0ls had Cam sensors and used sequential injection
So you could get wiring harness and computer from one of those
Also need to add the EGR system
EGR system is actually better for MPG because the computer can run a more aggressive spark curve because cylinders are not getting too hot under load
But yes, a switch to any sequential EFI will improve MPG
One of the biggest advantages of EFI is that the injectors can be TURNED OFF
Think about how an engine works
The pistons and valves create a low pressure/vacuum in the intake
A carb has Jets that this vacuum SUCKED fuel out of, EFI opens injectors to add fuel that is sucked into the cylinders
When you are driving and take your foot of the gas pedal the throttle plate closes and Vacuum goes way up, 20+"
In a carb that caused more fuel to be sucked out of idler Jets, and it wasn't needed
With EFI the injectors are SHUT OFF, no wasted fuel
With a carb many would shift to Neutral when coasting down a hill/grade, to save fuel
With EFI you want to leave it in gear with foot off the gas pedal so RPMs stay above 1,500, and injectors are OFF
Under 1,500rpms computer will restart injectors at idle levels, so you are using fuel
TPS(throttle sensor) is used for this
On a long downhill grade computer will inject fuel now and then to keep Cats hot
If you think about how anyone drives, speed up and then slow down, lol
With EFI you are not using any fuel when slowing down
So don't shift to Neutral and coast, leave engine in gear, and save some fuel, also save wear and tear on the brakes when using engine as the brakes on a downhill road