so my gm 3 bar map sensor doesnt sit at atmopheric when powered up but engine off. it keeps bouncing between 1.7 and 2.1". is there a way to recalibrate it to "0" like you can with a tps sensor based off of voltages or whatnot? im using neptune rtp.

 

Usually sensors like that are based off a calibration spec. There are a lot of different GM 3 Bar Map sensors with slightly different calibrations. I would look up the part number for the one you have and go from there.

 

Yes, what he said. I used to think that all GM MAP sensors were the same until I had to trouble shoot one while swapping parts. They can look the same but have a different scalar. On GM cars it can even throw codes.

 

that doesn't sound like a calibration issue, it sounds like either a bad sensor, crappy splices or a bad ground.
check and clean the thermostat ground, verify proper voltage and that the pins are in the right order, there's no corrosion and that the pins are making a solid connection.

 

ive been using them (gm 3bar) for around 8 years now and ive had 2 flat out go bad on me in that time. g101 is clean i just dropped the motor in and cleaned everything before i put it in. i solder all connections but ill check them. im also using that green rubber seal/grommet on the plug i may take that out i think the pins could go into the sensor more with it out...

 

well i bought another 3 bar sensor, and that damn thing reads 2.8" key on engine off...

i also have the stock map sensor wired in as well so i plugged that in for ***** and giggles. it reads between 0 and .1psi which is much much closer. the car runs better on that sensor too... (for what its worth the gm 3bar read high before i re soldered the stock plug on there so im removing that from my troubleshooting issues)

i check the volts key on engine off and its getting 5.01 in, 2.0 off the sensor output and the ground seems good i get the same results grounding right to the negative terminal. my settings in the neptune are 367 scalar and -45 offset.

i was looking around online and found it should be .2volts at atmospheric sensor output. im only moderately good with electrical things like this..