Hello, can someone please help me identify what this is? I just found it laying up next to the firewall on the passenger side. Where does it mount? Or can it
be eliminated?
Thank you all!

 

That is a Barometric Pressure sensor. There is no vacuum line that goes to the nipple on the sensor. It's open to the atmosphere and would have had an open cell foam filter stuck over the nipple to keep crap out of the sensor.

It can't be deleted unless your car is no longer computer controlled and has a mechanical carburetor and mechanical distributor in place of the computer controlled ones.

Picture below show where it mounts. It goes under the protruding lip on the cowl where the pencil brace mounts.

 

I believe its a stock map sensor.

 

Thanks guys! Any photos of where I need to mount it?

 

Mounts Here

 

It's a barometric pressure sensor, as described above.

It's not a MAP sensor, although it's very similar, and its function is related. For all I know its actual sensing element might be the same, and the whole assembly only different physically.

MAP is Manifold Absolute Pressure; which is, the exact pressure, in relation to a perfect vacuum, in the intake. The pressure in there can vary from perfect vacuum or 0 psi (not bloody likely) to atmospheric pressure which is about 14.7 psi at sea level.

The baro sensor reads ambient atmospheric pressure. Obviously this usually doesn't vary much, usually only within a couple of percent, at any given location. The exception occurs when changing altitude: at 10,000 ft for example, the pressure is only about 10 psi, which is only 70% or so of the pressure at sea level. The air at that altitude is much less dense, meaning an equal volume (carbs work off of air flow volume through the venturis) contains far fewer oxygen molecules. A carb's calibration therefore needs to change by that same amount as the air density's change to keep the mixture correct, at any given air flow volume.

Manifold vacuum, which is by far the most reliable indicator of engine load, is the difference between these 2 pressures. Without the baro sensor the ECM has no way of knowing the ambient pressure, and "assumes" that any pressure decrease below sea-level barometric pressure that the MAP sensor shows, is due to engine load. Obviously this is WRONG at high altitude. Adding the baro sensor provides more accurate air density info to the ECM. It was added in 84 to the carb setups in these cars. AFAIK no EFI systems need one, because they can vary the fuel over a wide enough range by injector pulse width, to keep the O2 sensor readings correct.

 

Interesting, yeah, my bad. I think some early gm efi cars use something really similar for map/vac/boost referencing. Makes sense that a carb car wouldn't use the same sensor.

were these baro sensors mounted near the driver side firewall on earlier cars? I remember something like that on my car in the late 90s prior to the first efi swap.

 

The MAP sensor is on the driver's side firewall between the brake booster and driver's side fender. It's keyed differently and uses a different color harness connector. I think MAP is green and BARO is blue. It's a 1 BAR BARO sensor and a 1 BAR MAP sensor.

1981 US spec 301 Turbo Formulas and Turbo Trans Ams with Computer Command Control have a MAP & BARO sensor on a bracket on the driver's side fender well. They are keyed differently with a matching harness connector colored differently. It's a 1 BAR BARO sensor and a 2 BAR MAP sensor.

I would assume all BARO sensors are 1 BAR because they only need to measure atmospheric pressure.

Turbo Buicks and 1989 Turbo Trans Ams us a MAP sensor for the boost gauge only. 2 BAR on the Buicks and 3 BAR on the TTA. The MAP isn't connected to the ECM though because these are Mass Airflow ECMs. Turbo Buicks with a digital dash doesn't have a MAP sensor and uses a 2 stage Hobbs switch to light the Low & High boost light in the dash.

I think on Speed Density cars such as TBI and TPI it takes a reading from the MAP sensor before the engine cranks and starts as a baseline for atmospheric pressure. With the engine off MAP and BARO will be equal.

 

That makes sense. Thanks for the info!