Do you still need an accurate MAP signal when the machine is not in boost? If so, you need a MAP signal clamp. The clamp allows the signal through, but puts a ceiling on it so the ECM never sees boost. A diode is not going to do that.
My '15 X ECM tolerated at least 8 psi of boost without a clamp.
I don't think any of the piggybacks include a circuit to condition the MAP signal.
If you buy a clamp, I would suggest you get one that runs on 12v. Some signal clamps require 5v, and adding another device to the 5v sensor power circuit feels like asking for trouble. IIRC all of the engine sensors are powered by one 5v circuit.
But first I would see if your ECM tolerates boost. If you can supply stable air pressure equal to the boost you intend to run you can run a test w/o even starting the engine. Pull the sensor out of the throttle body, find a piece of tubing that will fit over the sensor guard, turn on the ignition, apply psi and see if you generate an error code.
Hey guy's. you can search past posts. I have used the Dobeck/Silber piggy. It does not alter the OEM MATP sensor. It uses a separate MATP. The ECU does see over boost and will flash a code on gauge for high volt, but has no affect and goes away immediately after boost. I used a Synapse Missing link for over boost and had no affect The Dobeck type has slight transition hiccups. I switched to PWR CMNDR PCV boost, fuel, ignition with Autotune. This gives better tuning options. I have not finished the tune, almost done. Picked up a POD 300 and will add this soon. Use the PCV