here is the power flow for fourth gear....sounds like you might have
unplugged a electrical connector or didn't get it all the way in ...or
pinched or pulled out a wire during engine swap...//
FOURTH GEAR POWERFLOW
Fourth gear overdrive range is electronically controlled and
hydraulically activated. Various sensor inputs are supplied to the
powertrain control module to operate the overdrive solenoid on the valve
body. The solenoid contains a check ball that opens and closes a vent
port in the 3-4 shift valve feed passage. The overdrive solenoid (and
check ball) are not energized in first, second, third, or reverse gear.
The vent port remains open, diverting line pressure from the 2-3 shift
valve away from the 3-4 shift valve. The overdrive control switch must
be in the ON position to transmit overdrive status to the PCM. A 3-4
upshift occurs only when the overdrive solenoid is energized by the
PCM. The PCM energizes the overdrive solenoid during the 3-4 upshift.
This causes the solenoid check ball to close the vent port allowing line
pressure from the 2-3 shift valve to act directly on the 3-4 upshift valve.
Line pressure on the 3-4 shift valve overcomes valve spring pressure
moving the valve to the upshift position. This action exposes the feed
passages to the 3-4 timing valve, 3-4 quick fill valve, 3-4 accumulator,
and ultimately to the overdrive piston. Line pressure through the timing
valve moves the overdrive piston into contact with the overdrive clutch.
The direct clutch is disengaged before the overdrive clutch is engaged.
The boost valve provides increased fluid apply pressure to the overdrive
clutch during 3-4 upshifts, and when accelerating in fourth gear. The 3-
4 accumulator cushions overdrive clutch engagement to smooth 3-4
upshifts. The accumulator is charged at the same time as apply
pressure acts against the overdrive piston.
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