Hey hoping to get some helpful information here because I'm at a loss.. I bought a 1994 ranger 4.0 5speed manual 2wd it has about 267xxx miles and for the most part it runs good but gets horrible mpg like maybe 10-12... I have replaced plugs, wires, coil pack, fuel filter, fixed 3 fuel leaks it had put new bank one o2 sensors in when we replaced the clutch... I'm at a loss it idles a little rough like if you were not looking for it you probably wouldn't notice it... For the most part I try to keep cruising rpms under 2000 also.. Its not throwing any codes either.. Before I get asked yes I put all recommended plugs and wires in not just bottom of the barrel crap.

 

Welcome to the forum

Try this test
All fuel injection computers have a "Clear Flooded Engine" routine in their software
Cycle key on and off 3 times to build up fuel pressure
With key on press gas pedal down to the floor all the way and HOLD IT DOWN, at 0rpms and throttle sensor at Wide Open, computer will start "Clear Flooded Engine" routine
This means it will shut OFF all fuel injectors, but spark is still on
Now crank engine over, it should NOT start, it should not fire at all<<<this is good
Releasing gas pedal at any time will start injectors

This is a test for leaking injectors or FPR, so if engine fires or starts fuel is leaking in
(I use this every morning to start my high mile engine, gets oil pumped thru the system FIRST, so no dry starts, lol)

The 1997 and earlier Rangers use a Fuel Pressure regulator(FPR) on the engine end, it has the Fuel Return line and a Vacuum hose attached
On a 1994 4.0l the FPR is behind and below the alternator on lower intake manifold
Check its Vacuum hose for gasoline, if found replace FPR
If FPR leaks gas will be sucked into the engine causing Rich running and poor MPG, but it is odd there are no codes for that????

Does the CEL(check engine light) work, comes on with key on and then goes off while cranking and after start up?

Other issue could be...................odometer
Larger tires than stock size LOWERS odometer reading, so if truck doesn't have stock tire size then odometer in incorrect, so will show you traveled 120miles when you actually traveled 150 miles
This would explain why there are no codes, math error
Look on drivers door label for stock tire size

Lugging the engine also lowers MPG
4.0l OHV makes best power/torque at 2,500rpms
So when cruising 2,000-2,100 would be better

Also since you have a manual use the engine as the brake when going downhill, do not shift to Neutral
One of the benefits of fuel injection is that the computer can shut OFF the fuel injectors when your foot is off the gas pedal and RPMs are above 1,400
So when coasting downhill leave it in gear and rpms higher than 1,400 because fuel use would be 0, when rpms go lower computer will restart injectors at idle level

With carburetors it was the opposite, lol, fuel consumption went UP because of the higher vacuum when coasting, sucked more fuel out of the idler Jets