Acceleration issues 2002 dakota 4x4 quad sport 3.9l 4 speed auto.



Initial complaint. Poor acceleration. Hesitation. Very poor acceleration uphill. Hard to maintain speed uphill. Engine idles fine, rev limiter is at 4400 and no hesitation in park. But once in hear, forget it. Slow as can be getting up to speed.

Work performed.
Replaced 02 sensors
Downstream is currently disconnected and currently have a p0138 (02 circuit high voltage)
Replaced plugs, wires, coil, entire distributor.
Replaced TPS
Replaced MAP sensor
Replaced IAC
Replaced fuel pump/sending unit.
Removed CAT
Replaced Muffler
Changed rear diff fluid per spec.

Tested compression. 125/135 across all cylinders.
Tested all vacuum lines. No vacuum loss.
Removed and cleaned throttle body.
Tested intake belly pan for leaks, none detected.

At idle
STFT -3.1% TO + 2.3% (Fluctuates)
LTFT + 2.3%
MAP 12(inHg)
Load 4.7%
RPM 667 steady
Spark ADV 16 to 20
02 B1S1 fluctuated between. 10 to .90 v
02 B1S1 STFT fluctuates - 3.1 to + 3.1
02 B1S2 steady at 1.0 V
02 B1S2 STFT 99.2% constant (no cat)

So far at WOT the STFT AND LTFT both read 0.00.

Hesitation a little better after replacing sending unit.

Still an issue.
No acceleration uphill and hard to maintain speed even on 4% incline. Have to drop to 2nd gear or mash to the floor to get back up to speed.

New symptom

Truck lightly stumbles in all gears.
Hard shifts a bit.
Trans fluid is normal red color. No burnt smell and full, But with noticeable bubbles all along the dip stick.

Next step is to flush and fill transmission and adjust the bands.

Other then that, I am at a loss for ideas at this point. Thought I would pick someone else's brain. Any input appreciated.

Thanks!

 

The 3.9 is an undersized engine to pull a 4 door Dakota, so It will be slow to accelerate and hard to maintain speed uphill. The 3.9 5 speed extended cab I had was a dog, I had to wind it way out in each gear just to accelerate normally, an automatic with a 4 door would be even worse.

 

What brand O2 sensors? What type of plugs? Brand of crank sensor? Is it starting out in second gear??