the vacuum guage reads 19 inHg
30 (STP) -19 (running) =11 (actual pressure)
5psi -MAP reading while running
5psi= 10inHg
So 10 InHg is close to the same reading
I think the sensor is reading ok, I don't know if the pressure is correct.
Also, while driving and at idle, the timing advance reading from the scanner is all over the place. As I accelerate, the advance drops to 14*, as I decelerate, it jumps to 40*....at cruise or idle, it will start to wander. ( i can't read the timing mark on the crank dampener while it's running, but the strobe of the timing light shows a steady no wander situation against a stain on the dampener...and advances as it should) I can't compare a "proper" running truck to this one because I have never driven one before. It seems to cruise and accelerate smooth, with low end torque strong, but seems to lack horsepower. Still nothing to compare to.
Idle seems a bit low too.
I have changed out too many "obvious" things. never changes the symptoms. Only improvement was taking the o-ring out of the TPS which stopped the surging idle.

I'm starting to think the ECU (PCU) is the culprit. Possible a bad ground or short? The timing readings seem to be benign.

As for the tuneup parts, I changed out the cap, rotor, wires, plugs, o2 sensors, IAC, cleaned TB, replaced injectors, replaced CAT,
Nothing changed the performance, except the injector replacement added 100 rpm to idle and the o-ring I mentioned binding on the TPS

 

What brand O2 sensors?

The 3.9 was never a powerhouse to begin with. 2 or 4 wheel drive?

Could try resetting the computer, just disconnect the battery, turn the headlights on, count to ten, turn headlights off, hook battery back up, turn ignition to "on" (not start), count to ten, THEN start the engine, drive it like you stole it for 15 minutes or so, and see if it feels any better.

 

Denso sensors from rockauto.2wd

 

Good enough.

Give the pcm reset thing a shot, see if it behaves any better.

 

ok thanks