Hey guys,

I was taking out the ECM module on my 84 Trans Am to get the top off the AC dryer box when I found an empty vacuum port on the ECM module. What line goes to it and where does it come from? Any help would be greatly appreciated!

Ok, so the pics are too big and I'm running late for work. I'll try and re-size them after work but the question remains...what vacuum line goes to it?


----EDIT-----

Got the pictures re-sized (I'm pretty sure this is the ECM module anyway).

 

that is your map sensor, there is a vacum line that goes from there to the back of your tbi.

 

That sure looks like a MAP sensor but I never thought that 84's had 'em.

 

That's the barometric pressure sensor, and no vacuum line is supposed to go there.

It's supposed to have a square foam filter over it, but the foam typically has broken down and disappeared ages ago (you can make out its footprint in your first photo).

84's do have a manifold absolute pressure sensor, it's located on the driver's side of the firewall, tucked up in the corner.

 

There was no TBI option in '84, by the way.

 

yeah i typed that up without even looking at what year his car was

 

Thanks. I thought I had gotten all the lines hooked up and then I found that...man I panicked for a bit when that turned up!

 

Five seven is right on... the manifold differential sensor or baro sensor, is designed to read atmospheric pressure so putting a vacuum line on it will hinder its operation. it takes this reading and along with the vacuum reading from the manifold (taken by the map sensor from the rear carb port), sends this data to the ecm which basically calculates the difference between the two uses this data to adjust the correct fuel mixture and timing. Though they look the same they have different functions and part numbers and are not interchangeable. The map sensor is on the driver's side firewall and the baro sensor (manifold diff) is on the passenger side.
hope this clarifies things somewhat.