Hey all, the engine's getting a bit worn and feels underpowered in my 91 XLT 4.0 5spd. At times, typically in the morning job commute, it feels like its got plenty of punch, but making my way through afternoon traffic has me keeping it wide open in OD or 4th trying to accelerate at 65-75. It also has an inconsistent tapping which sounds like lifters to me along with lower oil pressure (at the N in "normal" once warm, middle when cold) since the last change with a PremiumGuard filter, and it also will run towards the hotter side of "normal" through slower speeds (through town, rush hour). I have a utility topper on my bed with material and tools, but with the small amount in there I wouldn't have thought that it would have this much of a power draw on a 4.0
I've pondered putting in a 5.0 V8 and drivetrain from an F150 of the same era, but recently came across a rebuilt short-block from a 1997-2000 (pistons and crank) as well as a supercharger from a 3.8 90 Cougar. Seller of the block says it would fit, just need newer heads, flexplate, dipstick, pan, all that. Would it be worth it to take the time to properly build and mate (if possible) that particular block to my older system and boost it if the sucker will fit, or would I be better off to duck the headache by just going with a factory reman?

 

Welcome to the forum

Reads like your throttle cable is stretched, Google: Ranger throttle cable mod
Simple fix to get full throttle back

You probably need a new Fan Clutch, when its going bad engine runs warmer at idle and slower speeds, thats when the fan is needed, above 35mph airflow thru rad is high enough so fan isn't used/needed

Yes, most likely a lifter going bad, the tapping, or loud fuel injector, it can come and go

There is no oil "pressure" sender on 1988 and up Rangers, they have an on/off switch, off if pressure is below 5psi, on if pressure is above 5psi, so any change you see in oil pressure gauge is electrical, unless if shows 0, then pull over, lol
You can change a 1991 gauge to be a "real" pressure gauge, need to pull the cluster and install a jumper wire and then change the pressure "switch" on the engine to a PS60 pressure sender

Yes, you can install any year 4.0l OHV 1990-2000 to replace yours, you can't swap 4.0l OHV heads around in all years
Good read here on the 4.0l OHV: https://therangerstation.com/tech_li...0rebuild.shtml


The F-150 5.0l OHV has a very TALL intake, might fit with body lift, but I would look at getting one(upper and lower intake) from an Explorer, complete with injectors
You also need the short water pump and accessories so.............almost better to get the whole Explorer with V8 for all the extra parts, i.e. exhaust

 

Thank you for the info!

I've just done the cable mod, can't wait to see if it makes a difference :D

That makes sense, though it just occurred to me, could the fan itself be robbing power from the engine when it gets hot? I flushed the system a while back and swapped the coolant with Zerex G0-5 HOAT in an attempt to solve the "running hotter" issue when I bought it but with little difference in the long run as you can see, and its slowly lost coolant as time goes on. The reservoir will bubble ferociously when stopped after a hot day of running warm during rush hour. Even after I get moving at a good speed after crawling through traffic, it'll take it a while to cool down with the hood cracked open. Along with replacing the fan clutch, what else should I do? I've heard of a radiator upgrade to a larger capacity, but haven't looked into it yet.

I'm running 4qt. Castrol GTX High Mileage to 1qt Lucas High Mileage additive through higher-grade filters like Mobile1, FRAM Ultra Syn. and trying a PremiumGuard this time around and changing every 3-4k. Would running a cleaner of sorts like High Mileage Seafoam through the oil before the next change be a good idea to clean out the injectors or create more problems with loosening up sludge thats sealing the oil leaks?

Oh! I thought 91 was one of the years that came with the true oil pressure sender, I'll be ordering that! (Or just replace with a Bosch gauge set)

That is some good info to keep in mind and reference later on if I end up getting this block. He's selling it for $650 currently, would this be considered a good buy vs. getting a brand new engine? It's a factory recondition that's been bored .030 over with new Motorcraft pistons, crank and cam, needs a flywheel, dipstick, oil pan, heads, lifters, manifolds and the like. I think I'll wait on a v8 mod.

 

Yes, you can install a Ranger 4.0l automatic radiator, its dual core, it just bolts in but.................
You usually need to change lower radiator hose to automatic model, upper works fine
AND, get a Automatic fan shroud at wrecking yard, it is not as deep as manual shroud because rad is thicker, it's almost impossible to get fan back on with manual shroud in place, lol
I did this upgrade to my 1994 4.0l manual trans, I got the fan on but headed over to the wrecking yard after I did

You can test your fan clutch
When engine is stone cold, pop the hood and try to spin the fan, it should be locked, hard to spin
Start engine, hood still open, you should hear locked fan grabbing air, a loud "whooshing", and that will go away after 5 seconds or so, as fan clutch unlocks
Shut off engine and spin fan again, should spin easily when unlocked

If it spins easily cold and then after startup replace it

 

Will definitely try that auto-tranny rad swap. With winter coming I'll prob just leave it till spring and do it with a cooling and AC system rebuild.

Did the fan test, don't recall hearing a "whoosh", but otherwise locked and unlocked as expected, prop change out the clutch with the system rebuild.

Accel. pedal definitely feels FAR better after zip tie fix, not sensing much power or high speed gain though, could I be having an issue with my injectors or fuel delivery system? I've got a bit of a hot-soak issue that comes and goes and I've never changed the fuel filter or pump.

 

Generally you will feel a power loss at higher demand/load and its often accompanied by pinging/knocking from lean fuel mix if your fuel pressure or injectors are limiting fuel flow to the engine
If your engine has a knock sensor then you would just feel the power loss

 

No knocking, just feels like it doesn't have consistent pick-up, mostly noticeable on hills and hard acceleration. Sometimes it cruises nicely, others I'm having to kick it down a gear or two to get it moving and even then it feels like I'm towing something.