I have a '99 ranger 3.0 4x4 all stock. Having trouble going up hills. Max I do up a decent hill is 55 mph in 4th gear pulling nothing. I have given it a tune up and seems to run smooth just powerless. I don't need gears to haul things just to get around commuting a little easier would be nice. I don't know my mpg per say though I know it's not very great. When I am on the interstate it struggles to do the 70-75 mph speed limit when I am traveling into a head wind. Any suggestions would be appreciated. I have heard something about exhaust having backed up cats? Idk much about vehicles. Thanks in advanced!

 

The stock gearing is 97 open 8.8" 2750 4.10 from what the door code says and truck is stock.

 

Reads like something is wrong, but could just be you are not used to the power band for the 3.0l.
Have a look here: The Ford Ranger 3.0L Vulcan V-6

3.0l Vulcan is a higher RPM engine, in 1999 model year the best torque is listed as 3,700rpm
My 4.0l has highest torque at 2,400rpm

Because of this the MPG is not that great with the 3.0l, and in a pickup truck that has the aerodynamics of a brick it is even worse, for any engine.

Torque is what gets you up the hills, horse power is what keeps you going, max. HP for 3.0l is at 5,000rpms.

The 4.10 ratio helps because it keeps RPMs high.

So for best power climbing hills or driving at speed you need to keep it above 3,200rpms

Stock tires, P235/75R15, should be about 27" diameter, if you go larger that will effect top speed power, because RPMs will be lower.

Assuming 27" tires:
At 70mph in 4th gear(1:1) you should be at 3,500rpm so in the torque range
In 5th(.75:1) you would be at 2,700rpm so response would be sluggish, and maintaining speed would be harder, i.e. the head wind

At 55mph in 4th you would be at 2,800rpms
in 3rd you would be at 4,200rpms


You could check compression to see if there is a problem.
Compression on a 3.0l, engine cold, should be about 170psi at sea level to 2,000ft
All spark plugs MUST be remove for a compression test.

Write down results for each cylinder

If they are lower than expected then repeat test but add a teaspoon of oil to cylinder before testing(wet test), pressure will go up but it is the amount it goes up that will tell you if it is rings or valves that are leaking compression.
Compression is the source of torque and horse power.

How many miles on the engine?

What did the old spark plugs look like?
light brown coloring means clean burning, darker color can be rich mix or oil leaking in, either lowers power

 

Just changed out the plugs they were a brown color apart from one was wettish black on the threads. How much RPM's is to much when driving the 3.0? I am newer to this make/model I'm use to driving a 350 sbc 1500. Motor has 204k miles on it sounds smooth but just doesn't have any high end that I have experienced but I have been shifting at 3k RPM's. Should I let it hang around 3.5k RPM's? Would this be hurtful to my engine? Thanks a lot of helpful info RonD.

 

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Yes, you need to be running and shifting at higher RPMs with the 3.0l

245/75R 16" are 30" diameter, off-road package size.

So at 70MPH in 4th RPMs should be 3,200, comfortable torque range for 3.0l

In 5th it would be down to 2,500rpms at 70mph.

The power band for this engine is at higher RPMs, that would be hard to get used to but that's the way it is with the 3.0l.

Yes, 3,200-3,700rpm would be where you would have most power.
It won't "hurt" the engine, that's just the range it has the most torque.

 

Would it help to drop the tire size to P235/75R15 27" Diameter? Or should I just keep what I have?

 

Smaller diameter = larger ratio.

30" tires with 4.10
If you changed to 27" then ratio would act like 4.56


So RPMs would be higher overall at same speed, it would add about 300rpms to above
so 4th gear at 70 MPH would be 3,500
5th gear at 70 mph 2,800rpm

 

So, If I understand you correctly based on the torque range with the higher RPM's this would be better as far as getting around easier. Perhaps MPG a little better?

 

MPG has a lot to do with driver input.

air:fuel ratio for gasoline is 14.7:1
This is a WEIGHT ratio not volume, so if there is 14.7 pounds of air, 1 pound of gasoline would be needed.
This is why 200MPG carbs were not real and hidden by the oil companies, lol, and why "pre-vaporizers" are silly ideas, these are all "volume" based which reads well but simply isn't the way gas engines work.

One thing that is volume based is the engine displacement.
2.0l engine uses 2 liters of air every 2 RPMs, 2 rpms because it is a 4 stroke engine.

3.0l uses 3 liters
4.0l 4 liters
ect..........

The more air an engine can use the more fuel can be added, so the more power it can make, bigger displacement more power.
Turbo and Super chargers increase the air volume an engine can use each 2 RPMs so increase the amount of fuel it can use and the power it can make.

Running an engine at higher RPM means more air is used so more fuel is use, so that would mean less MPG...............but
It isn't as simple as that.

A 2.0l engine gets better MPG than a 5.0l engine, but not always.
If you put a 2.0l gas engine in a 7,000lbs vehicle, it's MPG would go way way down, performance would suck as well.
5.0l in same vehicle would get better MPG.
This has to do with "load" on the engine, 2.0l has to run at maximum load all the time, 5.0l doesn't

Driving the 3.0l at lower RPMs means you will have to push gas pedal down more because you are out of the power band, engine load is high.
Yes you are using less air and fuel but engine is not running efficiently because of that.
At higher RPMs you are using more air but getting more power from the fuel you are using so better MPG for the power needed.

3.0l is not great for MPG, better than the 4.0l but not by much

 

you indicated that one plug was wet and black. Did changing to new plugs change anything? If not check that fuel injector is working O.K. or that you have a good connection on the plug.

 

Thanks for the patience RonD that is alot of info and very detailed I appreciate it! Sure helped me have a better understanding how things work. Granger, I changed the wires and plugs and did an oil change it still runs the same. Furthermore I have done some test drives at higher RPM's and it seems to be taking it very well doesn't seem hard on the engine like I thought it would. Use to driving a granny 5 spd sbc haha. I thought of a few modifications I seen on that link RonD sent. K&N filter and new exhaust system to help out airflow. Going to drive it for a few days and check that plug again and see if it is getting wet and black again. I don't know how to check injectors or anything.

 

235/75/15 is a 29 inch tire. a 27 inch tire is from a 14 inch rim. according to tire rack sizing info. i suspect your truck will run better with 29 inch tires. that's what is on mine and i have a 4 liter.