90% of driving is around town and rarely does the transmission shift into overdrive at 45 mph. It would help a lot if it would shift at 40 mph. Can it be programmed to shift earlier?

 

Shifting is based on RPM, engine load and speed

What engine do you have?
2.3l
3.0l
4.0l

You don't want RPMs much lower than 1,800 in any "gear", 3.0l would be better at 2,200

 

Engine is 4.0L and rear differential is 3.55 ratio.

 

You don't want to be in OD at 45mph, even at 55mph would be questionable with 3.55 ratio

4.0l SOHC engine makes best torque/power at 2,900RPM
So for best MPG you would want to be 2000-2,200rpm

You can go here and plug in your numbers: https://www.crawlpedia.com/rpm_gear_calculator.htm

3.55 ratio
29" tires???
Speed 45mph
Transmission ratio, 4th gear is 1
OD is .75
3rd is 1.47

In 4th your RPMs would be 1,850, so low, engine is lugging a bit but MPG is OK unless you are going up hill
In OD RPMs would be 1,388, way to low, MPG in the toilet

To keep vehicle rolling down the road requires power from the engine, the farther you are away from max power, the more fuel it will take to keep the vehicle rolling
IDLE is of course the worse MPG, i.e. 0MPG, because you are not moving, lol

 

RonD, Thanks for the great site for calculating engine RPMs. I should have done my home work before asking about changing the 5th gear (OD) to engage at 40 MPH. After doing a few test runs with a slow acceleration I determined that the 3rd gear is shifting into 4th gear at 39-40 MPH. 4th gear is shifting into 5th (OD) at 45-46 MPH.

I calculated the engine RPM at 40 MPH (4th gear) to be 1,787 and engine RPM at 45 MPH (OD) is 1,500. At 65 MPH in OD the calculation is, 2154 RPMs. An actual test drive was closer to 2,075 RPMs. Most of my OD usage is an occasional short trip of 40--60 miles at 55 MPH (1,850 RPM) to 67 MPH (2,200 RPM) .

My first full tank after much needed plugs and wires was 15.4 MPG. Is there anything that you see in the shifting of gear 4 or OD that has a chance of helping? If injectors are dirty, I'm counting on the use of Sea Foam as a possible remedy for that.

 

How many miles on the upstream O2 sensors, the 2 closest to the engine?

These need to be changed at 125k miles or MPG will start to go down slowly

These are the ONLY sensors that for sure wear out, they use a chemical to detect oxygen in the exhaust, so they simply run out of that chemical, as they do they cause computer to run the engine richer than it needs to, so lower MPG
Change them if you are not sure, they pay for themselves in better MPG over the next 125k miles

2004 Ford Ranger 4.0l automatic 2WD is rated as 15mpg around town, 20mpg on long road trip(200+ miles) at say 60mph

So your 15mpg is what it should get for your driving conditions

Also are you running stock tire size?
This is important if you are using odometer for calculating MPG, larger tires show lower odometer reading so lower MPG

 

Thanks for the O2 sensors tip. I've only had the truck about 5 years and I have very little history. I suspect the sensors are OEM. Tires are stock size, 225/70R-15
Thanks for your help. Appreciate it!

 

If this was my truck, I would be turning off (OD) until I was at 55 MPH, your RPMs are pretty low, I think you would get better mileage at a higher RPM.

I had a Dodge that came with 3.07:1 gears, performance and gas mileage sucked, I put 4.10:1 gears in it, performance was much better, and gas mileage went from 12 MPG to 15 MPG, it was like driving a totally different truck and got better mileage.

 

Yes, +1 ^^^

Lower RPM for better MPG is not always the case if you are lugging the engine, it requires more fuel to increase speed unless you are nearer the power band of that engine
OD OFF for awhile and see if numbers improve

 

Thanks. Will try it. The OD will be off, unless over 55 MPH, for the next tank of fuel.

 

Does the OD being off effect the "faux 2nd gear"?

If I remember correctly, 2nd gear in our trannies is actually 1st AND overdrive engaged simultaneously.

Maybe the transmission's control module employs the OD for 2nd even if the OD is switched off?

 

No, it would still shift to 2nd gear(1st + OD) as needed

 

Sorry, but I'm not understanding the last 2 post about 1st, 2nd and OD. Explain more?

 

The 5R transmissions are rated as 5 speeds, but really don't have the planetary gears for 5 speeds, mechanically they are exactly the same as the previous 4R 4-speed transmissions used in Rangers

Ford engineers added a "faux" 2nd gear by turning on OD while 1st gear planetary gears were still engaged
This idea came from the off-roaders using the A4LD(4R/5R's grandfather), which was the first transmission with OD solenoid shifting, 1988
They ran a wire from this OD solenoid to the cab, so they could turn on OD in every "gear"
A4LD was a 4-speed, so this changed it into a 6-speed
Gear and ratio
1st - 2.47
1st + OD - 1.86
2nd - 1.47
2nd + OD - 1.2
3rd - 1.0
OD(4th) - .75

In the 4-speed the 2.47(1st) to 1.47(2nd) ratios are quite far apart, so engine had to run to higher RPMs in 1st before shifting to 2nd or engine would lug down
By adding the "faux" 1.86 "2nd" gear the shifting could be done more smoothly, and in off-roading having this 1.86 ratio was a big benefit at slower speeds
2nd gear with OD on is not a big benefit, so that wasn't used by Ford, or most off-roaders, lol

So Ford added it(OD on in 1st) to the computers software and changed the model number to 5R55E from 4R55E, and of course advertised the "new" 5-speed transmission
2nd in the 5R is an actual "gear ratio" so the "faux" is a bit of a jab at Ford

 

Thanks for the details. Is there a MPH at which the manual engagement and disengagement could result in damage to transmission?

 

No.

You can turn it off and on at any speed.