OD problems often boil down to:

1) Bad wiring - with the switch on and it in 4th gear you need 12 volts positive to one side of the solenoid, and ground to the other. With it dead quiet you should be able to hear a small click from the OD when you turn the switch on. If you don't get 12 volts at the OD, track backwards. If the 4th gear switch is not working, try to avoid bypassing it (it is very hard to replace with the transmission in the car) because otherwise you might leave it on and either over torque it in a lower gear (especially with the B30) or use it in reverse which supposedly can tear them up quickly.

2) Low oil - typically they gradually start to engage harder after being disengaged, engage slowly, occasionally disengage. Just make sure the trans is filled to the fill hole.

3) Bad solenoid - sometimes they get full of oil and start to react very slowly, sometimes the O ring on them leak and allow it to engage regardless, sometimes the windings just fry and it doesn't turn on. Suspect it last after checking the wiring and oil level first.

4) Internal wear, beyond my tinkering ability, other would know more. There is a little oil pump working on an eccentric on the input shaft, it needs to pump some pretty good pressures to get it to work. There is a filter under the cover, might be a last step check before pulling the entire thing off.
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I'm JohnMc, and I approved this message.