When you turn the key to "on" (engine off) the MAP senor should read the local barometric pressure. If you live at sea level, you will see close to 5V between the green wire and the black wire. If you are above 1,000-ft elevation, you will get lower voltage as altitude increases. When you start the engine, at idle, closed throttle, with the stock cam, you should see about 1/3 of the barometric pressure. A typical reading would be about 1.3 to 1.4V.

And again you have to make sure you have 5V reference between the gray wire and the black wire.