Issue with boost datalogging on MAP sensor

Hey guys,

I’m having an issue with a newly installed 3 BAR MAP sensor reading incorrect values in Live Link, reading super high and pegging out. Using analog 2 on the firewire (red) as my wideband is on analog 1 (orange). The setup is:

• Boost line teed off from factory yellow boost line in glove box into MAP sensor
• Using a 5v inverter connected to a switched 12v source. I verified 12v input and it is putting out 5.09v output. This 5v output goes to the positive/reference wire on the pigtail of the MAP sensor.
• MAP sensor ground wire to chassis ground
• Signal wire (middle wire) on MAP sensor goes to firewire analog 2 (red wire)
• Analog ground wire (green) grounded to chassis

Formula is the preset one in SCT Live Link which is something like (v*9.78)-14.7. I also tried a similar one from a how to data log boost thread here on SVTP. Both of these equations are putting out like -0.7 readings when idle, and just tapping the throttle at idle (staying well under boost levels) is sending the value to 10+.

I rolled into the throttle on a quick drive and hit maybe 15 psi on my aftermarket gauge, and the MAP sensor peaked right out at 32ish well before I hit 10 psi.


The interesting thing is, when I change the formula in Live Link to just show volts (v), it shows 4.98v with the key on but the car off. So with the correct formula applied, it’s maxed out at 32 psi value with the car off.


Any ideas to what is going on here? It’s obviously reading data and communicating with the software, but the numbers are way out of whack.

The MAP sensor I got is a knock-off but has great reviews on amazon, here’s the link:

Is it wired like this? Guessing it's a gm 3bar?

Sent from my SM-G991U1 using Tapatalk

rymax101 said:

Is it wired like this? Guessing it's a gm 3bar?

Sent from my SM-G991U1 using Tapatalk

Click to expand...

Affirmative. It's a 3 BAR knock-off GM replacement, the part number matches the GM/ACDelco part. See amazon link.

Suppose I could order another and swap it out, the pigtail is already wired in.

Actually I can't, looks like the pigtails on most of the GM ones are male pigtail and female on connector, mine is opposite.

I may have just realized what the issue is, this may not be a "3 bar" sensor, looks like a generic MAP sensor, could be a 1 bar or 2 bar, however others that look identical on amazon ARE listed as 3 BAR...

Still doesn't make sense that it would read 5v when the car is off unless the sensors are inherently much different.

Also, check that your ground has good continuity to the negative terminal. If ground isn't good there will be little resistance for the sensor.

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Went ahead and ordered a different one on ebay that is confirmed that style plug and 3 bar. Seller even put the reference volts for psi in increments. I'll wire that in when I get it and report back. Good chance this sensor is just a junk/1bar one.

Edit: I think I was able to finally wrap my little brain around this. It makes sense that it is reading 5 volts with the car off... If it's a 1 bar map, it's reading atmospheric pressure which is 1 bar... So yes it's maxed out with the car off. When I ran it under vacuum, it was showing values up until I went from vac to boost, making it peg instantly.

Big brain stuff going on here