Hi all. I've been lurking and researching on here for almost a month as a guest trying to crack this problem, and I've (finally) registered so I can post the question... ...if any of y'all like a good mystery it'll be worth the read ;-)
I've got a 2002 2wd Ranger with a 2.3 I4, and the thing won't rev past about 3,000 RPM - even with no load on the engine. I'll summarize what I've tried thus far below, and I'd greatly appreciate any advice on how best to move forward...

1. The truck was running a bit rough throughout the rev range and was lacking power. Any kind of acceleration attempt and it just bogged. I hooked it up to a cheap code reader and it was was logging misfire DTCs on multiple cylinders.
2. Inspected the coil: found cracks in the coil housing and a cracked connector on the low voltage side.
3. Replaced the coil, plugs, and wires; wired on a new low-voltage connector. Still ran kinda lousy and lacked power (hadn't yet tested for max-rev top-out).
4. Checked for spark with an inline spark tester, and the indicator flashed regularly.
5. Checked spark strength with an adjustable gap tool and spark jumped 30 kV no problem.
6. Now noticing the "won't rev past ~3,000 RPM" problem.
7. Suspected a clogged Catalytic Converter because there's a mechanism of failure: Bad spark --> incomplete combustion --> fuel in the Cat --> melts Cat --> clogs --> restricted flow, won't rev high.
8. Hooked up ForScan to read MAF and MAP PIDs. Appeared normal at low engine speeds (no load), but at higher no-load speed (~3,000 RPM), the MAP would climb and not recover i.e. "less vacuum". This (I thought) was an argument for a clogged Cat - I'm commanding more engine speed (volumetric flow) by opening the throttle, but the engine is not able to respond (restriction), and the MAP rises as a result.
9. At this point I also see DTCs for system too lean - and think vacuum leaks (more on that later).
10. To decisively diagnose a possible exhaust restriction I measured the exhaust pressure at the O2 sensor upstream of the Cat. Less than 3 psi at all engine speeds (up to ~3,000 RPM, obviously). The exhaust isn't restricted.
11. Now onto the system too lean codes and vacuum leaks. Inspected vacuum lines - found no leakers, but found a collapsed PVC hose. Replaced the hose (but not the PCV - I gotta deal with that retaining clip/nut and I'm putting that off 'till I get this current problem sorted).
12. Hooked up to ForScan again to dive into SSFT and LTFT PIDs. They seem strange to me. The LTFT is maxed at 25% at an idle, but drops to low (-) %'s once you open the throttle. STFT is high until the motor maxes out and won't go faster. I don't have a lot of experience reading these, so I'll attach a screen-shot. It seems to me the system is too lean up 'till the point where I'm commanding higher speeds but it won't rev higher, and at that point it's actually rich. Sorta pointing to fuel delivery?
13. Without really being able to interpret the fuel trim PIDs, I start thinking fuel delivery problem. System can provide enough fuel for low-rev / no-load, but at high revs or any load, there's not enough.
14. Change fuel filter - no changes.
15. Measured cylinder compression (just b/c I had the tool) - Didn't record the values but all were in-spec and didn't vary more than 1-2 psi across all four cylinders.
16. Measure fuel pressure at the rail - 65 psi from an idle all the way up to ~3,000 RPM when it won't spin faster. BTW, total PitA finding a tool that would hook to the Schrader valve. DM me if you ever need one.

At this point I'm down to clogged injectors or...??? But before I invest the time and $ in that, I'd love to get a positive diagnosis.
This is a spare truck for errands, so it's not an emergency, and I'm also not able to invest a ton of loot into it. Any help would be eternally appreciated.

 

Are you trying to rev the engine up past 3000 rpm while in park or neutral ? If so, there is a rev limiter that won't let the engine go past around 3000 rpm while in park or neutral.
Take it out on the road and wind that puppie up and see if problem still exists.

 

@Grumpaw I *did not* know that!!!! Holy moly! Time for a road test!

 

Welcome to the forum

Manual or automatic transmission?

All engine computers have a REV Limiter and its usually set for 3,000rpms, in Fords it is set for 3,000rpms
This is triggered by clutch pedal switch showing "clutch pedal down"
or
If Automatic its showing trans is in Park or Neutral

These are switches, so can fail to connect or short so always connected
Depending on which switch this can initiate the REV Limiter in computer even for driving
Speedometer signal will also cause REV limiter if it shows 0MPH

Dirty fuel filter or clogged exhaust can do the same but the specificness of 3,000rpm mark would tend to eliminate these, but not completely because it could just be they are displaying symptoms at 3,000rpm so a coincidence it matches computer 3,000rpm limiter

Fuel trims are OPEN TIMES for fuel injectors
+25% means injectors need to be opened 25% longer than computer originally calculated to get a good oxygen level from O2 sensor, computers calculation is STFT 0

 

@Grumpaw That was it 100%. The lean code I was seeing was probably from a small vacuum line I knocked off while replacing the PCV hose. I put it back on and I'll hop back on ForScan to confirm.
After a road test, it revs to 4,000+ RPM and pulls like a champ with no misfires. It was the coil the whole time and I went down that rabbit hole of diagnostics because I didn't know there was a stinkin' rev limiter! Weel, I learned a lot along the way.

Thanks a million man....

 

Went thru the same thing 1 1/2 years ago and then remembered reading about Fords and rev limiters.
Glad it was just a simple fix for you.

 

Mine is doing this too. I'm not the shadetree mechanic I was in younger days. I have a trusted one. Wondering if this is / will be an expensive fix?