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Hello all,

First time poster, long time lurker. This site has helped multiple times when keeping the wife's Gen 1.5 V on the road.

But this time, I'm near the end of my diagnostic tree without shotgunning parts and I was hoping for a more solid direction to head.

First, the specs:

2001, 180K on the original engine and trans (RT4WD, 4AT/MDMA trans)

3 qt drain/fill at 160K (when we bought it), and again at 180K with Honda DW-1 fluid. Previous history is unknown.

Transfer box needed repacement due to bearings being DESTROYED (figured it was due to off-roading as resonator is dented, mud everywhere in the engine bay and a bad front U-joint). Magnet on drain plug looked like a Chia-Pet.

New thermostat since the old one wasn't sealing and would allow intermittent lock-up due to temp fluxuations (unknown how long that went on).

The Problem:

Most of the time, on a lite/part throttle, the trans will SLAM into 4th gear. Real sharp shift, but no slipping, studdering or hesitation. Sometimes a "rushed" 1-2 change, but 2-3 are silky smooth and no shift flare, no delayed engagement, both semi- and full-lockup occur and disengage under acceleration, and downshifts are snappy and smooth.

The Investigation:

I've tried running down the FSM for hard 3-4 shifting such as changing the fluid, tired motor mounts, bad/wrong TPS and stuck shift solenoids. I'm down to either a stuck CPC valve (interal trans) or some problem with the 4th clutch. Very rarely will the trans shift easily/smoothly into 4th on part throttle (cruising).

-Pulled the A/B Shift solenoids, they are strong and clean (gasket/screens were clear as well).
-Fluid was/is clean and red. No signs of burning or contamination.
-TPS is working perfectly, even through a data scanner (no bad gaps or wrong TPS % readings)

The Kicker:

The trans will shift smooth as butter under hard accel. If accelerating to highway speeds, the 3-4 shift feels like the 1-2 or 2-3. It feels like a 10K mile trans.

What I think is going on is the 4th clutch is seeing ful line pressure even under part throttle. This pressure is goverened by the CPC valve. This valve might be stuck due to the old transfer box going nuclear and sending metallic particles through the system.

Ideas before I pull this thing apart and look?

P.S. I'm not sure if this is an issue or not, but with my hand-scanner, the MAP sensor values (inches. Mg) reads ~7.0 at idle, 22-23 at WOT, and ~14 on engine braking. I know this should be reverse (from conventional knowledge) and the computer doesn't seem to mind as the Long Term Fuel Trim is hovering around +3.1 and gas mileage is around 24 mpg avg.

But could this "wrong" MAP reading cause the PCM to calculate higher load and therefore higher line pressure for the trans causing the hard 3-4 shift? Just kinda spitballing here..

Thanks in advance!
 
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