I own a 1990 Integra and i recently put in a OBDO JDM B16A.
My problem is that my vtec doesn't work because of my speed sensor.
I've already tried new speed sensors but here's the thing, when I insert the speedometer cable's end into the speed sensor and install the retaining clip, I spin the bottom gear of the speed-sensor and the needle on the speedometer jumps naturally. But when I install into the transmission, it doesn't work??? I don't know what the problem can be because I don't really know the internals of a transmission. And when I drive, my car pops out of 5th gear? Do any of these things and problems add up? Or are they completely different?
All the replies are much appreciated

 

Check to see if the gear that powers the Speed Sensor has come unseated from the Differential inside the Trans. If that is the case, the only solution is to open the Trans and pull all of the gears. After that you can repress the VSS Gear onto the diff and put everything back together.

You can check this by pulling the speed sensor shining a flash-light down into the hole of the trans and trying to manually move the gear by hand.