My autometer boost/vacuum gauge shows -17 in. hg and my obd II scanner shows -11 in. hg of manifold pressure in my engine. Which one is accurate???

Neither are going to be perfectly accurate, but I would trust the Autometer gauge more. The datalogger is just reading from the stock MAP. Its main function is for fuel delivery, not accurately reading pressure in certain units. As long as the MAP gives about the right output, the engine will run fine. The sensor may not be calibrated and there are several electrical connectors in the line from the sensor to ECU. It works well enough to keep the engine running within specs, but I wouldn't expect the datalogger's pressure reading to match a real gauge. There are manufacturing tolerances on the Autometer gauge too, but I would still trust it more.

Corbin

'95 ESI-T
HRC+FMIC+ETC...

Corbin
'97 GSX dressed like a '95 ESi