I have a 1987 4x4 Ford Ranger with 5 speed tranny and the ever so loved 2.9 liter engine with 33" tires....The truck has been running fine for the last two or so years until recently,,,I've noticed will going up a hill that I have a significant loss of power....I mean I can push the pedal to the floor and have no acceleration what so ever.....So I began testing it out and come to find out if I am traveling along 55 or so and floor it it has very little to almost no acceleration capbility. It seems to lack top-end power all together.
I have started a troubleshooting process of elimination to find a cure for this problem but have had no sucess....I have done a basic routine maintenance tune up with new spark plugs, oil change, air filter, etc.... I have replaced the fuel pressure regulator, both of the fuel filters and the fuel sending pump within the gas tank.....BUT I still have the sluggish problem.. Somehow it only seems to do this under loading conditions though.. The reason why I say this is I can be going up a hill with it floored and it losing ground speed substantially but if I push in the clutch with it floored the engine revs up with no problems... this leads me to believe it could be some other problem than the engine...I'm not sure though....If anyone has any ideas I am open to suggestions.....Thanks..

 

it may have something to do with it being 20 years old. normal wear and tear, idk

 

No, I've owned three rangers other than this one...and trust me I haven't
got all of the goodie out of this one yet... The engine has good compression...Truck is in good shape...Its just an odd symptom to troubleshoot......I'm basically elminating starting at cheapest possiblities first and proceeding to the more expensive alternatives....

 

maybe you are not getting good spark? coil? running hot? timming off?

brakes dragging?

what if you down shift into 4th? does fine? with my old truck i always had to down shift if i wanted to accelerate.

 

Does the same when down shifting to fourth...
No overheating....
I haven't checked the timing... This could be a possibility...
But at current it has no riugh idle or skipping.. It runs very smooth
other than top-end....
I read something about vapor lock... What are the possibilities for a
pressurized electronic fuel system to be getting vapor locked when the
engine gets warm?

 

I have the same thing, I just bought my 1987 (5speed 4x4) with the 2.9, BUT mine is SLUGGISH on the "flat" highway going at 55 mph (sometimes slows to 50mph staying around/under 1800 rpm). the previous owner did the "basics" on this also, so it likely was an ongoing problem before I bought it. Im glad I am not dependent on the truck 'until winter...which gives me time to work on it.

 

First thought is worn valves and valve springs.After 21 years the springs get weak and allow the vavles to 'float' meaning they don't close fast enough or all the way. This will lead to burnt valves if let go too long.
Do a compression test . If the lower end is good get a valve job.