GM 3BAR MAP Sensor Install and Scaling

[m sprank]

So, If you are running big boost (23psi or more) you are maxing out the OEM 2.5Bar MAP sensor.

 

After much research the cheapest, most accurate solution seems to be the GM 3BAR MAP Sensor.

 

Which GM sensor though is VERY important. Only the MAP sensor out of a 1989 TransAm 3.8l V-6 Turbo will work. GM part number is 12223861. I found one at NAPA for $65. NAPA part number is 2-19481. You will need a GM electrical pigtail too. GM part number is 15305891.

 

Install is straight forward.

 

Terminals;

A=Ground (Black with yellow stripe on LGT)

B=Signal (Orange on LGT)

C=5V (Black with blue stripe on LGT)

 

Just splice the GM pigtail into your harness and find a suitable mounting location. Then connect the tube from the manifold.

 

Now you need to rescale the sensor. On 2007+ cars with the air pump this is sooo important. If you do not rescale the car will not start. You will throw P2431. This is the secondary air system sensor verifying atmospheric pressure. If atmospheric and manifold pressure are vastly different at key in on position, no start.

 

Now for scaling. I use Romraider which allows an offset and a multiplier.

 

The cutsheet on the GM sensor shows a voltage of 0.501-0.761 at 40kPa. It shows a voltage of 4.784-5.044 at 304kPa.

 

So, if Y = MX + B, then

304-40 = 264kPa

(0.501 + 0.76) / 2 = 0.631v

(4.784 + 5.044) / 2 = 4.914v

4.914v - 0.631v = 4.283v avg difference

 

264kPa / 4.283v = 61.639kPa/v

304kPa = (61.639kPa x 4.914v) + B

B = 1.106kPa

 

61.639kPa = 8.9399psi this is your multiplier

1.106kPa = 0.1604psi this is your offset

 

Offset on this equation is a bit odd. Multiplier is always stable. Here is the reason. Depending on when you convert to psi the offset changes.

 

If you convert to psi right from the beginning you get an offset of 0.1608.

 

If you convert to psi at the end you get 0.1882.

 

So, I took the average of the two which is 0.1745.

 

 

So my final (pre-boost gauge verification) scaling is;

Offset = 0.1745

Multiplier = 8.9399

 

Per the GM cutsheet the max voltage should be set to 4.94v. Minimum voltage should be set to 0.02v. I left the CEL threshold at 8.

 

These settings give me a reading of 14.4psi with the car off and ignition on at sea level. I used my Fluke and verified the sensor is putting out 1.606vdc stable. But the ecu is reading 1.577vdc. Not sure where the voltage drop is occurring. Not sure if it is stable (I need a boost gauge). Because of this I adjusted the offset to 0.6045. This is giving me a reading of 14.65psi which is exactly what it read stock.

 

I I have verified the scaling with a boost gauge. But, every sensor will have slight variance and every car will too.

 

I hope this helps anyone else who is currently running or planning to run more boost than the 22.5psi that the OEM MAP is capable of handling.

[rao]

You would use GM parts in a Subaru

 

Great info gathered into one place

[m sprank]

Would use them in a BMW too, Lol.

 

Cheapest thing I could find to do the job. Kind of like an LS-1 swap.

[Spec B]

Bumping this up for a little help.

 

Looking to go to a bigger MAP sensor - wondering if anyone has tried this scaling on a 05-06?

 

I am still on the stock MAP sensor and my boost STRI electronic boost gauge is reading 24.5 PSI - although I am barely hitting 22 (21.85) when I log. I need scaling will be pretty close since my boost gauge is way off.

[m sprank]

Scaling on 05-06 should be the same. You will need some info from the sensor manufacturer and you can then plug the numbers into the equation.

 

Many customers using the AEM 3 and 5 bar sensors and the Perrin sensors.

[gordata]

Sorry for bumping this but where is a good place to mount the 3 Bar Sensor? I was looking for a bracket if one existed but did not find much info for legacy/wrx application, only for metal manifold.

[m sprank]

Where ever you feel like it. Depends on how much wiring you want to do. If using a GM you will have to get creative for a mount.

[gordata]

Any pictures of where you have it mounted so I can steal some of your idea? Lol

 

Sent from my Nexus 10 using Tapatalk 4

[m sprank]

I ran it for about 1 month. It was a band aid. I made a custom aluminum mount for it. I use AEM sensors otherwise.

[acumenhokie]

Does this apply to 5th gen LGT too?

[m sprank]

Scaling is scaling. The math is always the same. Every sensor (Omni, AEM, etc) have different scaling. I have never swapped a MAP sensor on a 5th gen. You would need the wiring diagram to verify power/ground/signal and then you would need to re-scale the sensor via the AP tuning software or Ecutek (whichever you are tuning with).