Hello All, Can someone please help me identify what this vacuum tube with the brown end is for on a 1984 Z28? I believe it is a transmission vacuum tube??? It was connected to the back of the carburetor and is in the wiring harness running along the bottom of the firewall over the transmission. Also, what is the barbed vented opening in the intake manifold? Is that for Cruise control? My Camaro does not have cruise. I am installing a Sniper 2 EFI system and not sure if I need to connect the vacuum tube and just plug the new intake manifold.

 

The line goes to the MAP sensor, which is near the brake booster. You'll need it if your EFI system uses the stock one, or mounts its own in the same place.

The barbed fitting is the vacuum takeoff for all vacuum-operated accessories. Including cruise in cars that have that. Butt also, the vacuum diaphragms that direct the air in the HVAC system.

 

Thanks Sofakingdom! I though my MAP sensor which is like some sort of barometric sensor on my 1984 was this item in the photo which was mounted on the passenger side top of firewall. There was no vac tube attached to it and supposedly it does not require a vac tube connected to it. I will try and trace the vac tube with the brown end and see if I can figure out where it goes. I don't see any vac lines over by my brake booster other than the black plastic cylinder (which I was originally told was for Cruise control) mounted to the firewall that had a rubber hose from the intake manifold barb and the other long vac tube in photo that goes over to the passenger side. Those were the only 2 things connected to the black plastic cylinder. Maybe this longer black vac tube is for directing air in my HVAC system? I believe the Sniper 2 EFI has a built in MAP sensor but I will give Holley a call to confirm. I'm not sure what factory items I need to leave and which ones the Sniper 2 replaces I can remove. There is a lot the Sniper 2 replaces on my ECU that used to control the carb. I'm sure I will get a check engine light on my dash and will need to have some codes deleted from my ECU.

 

The thing with the blue connector is indeed the baro sensor, and doesn't get a vacuum line because it's measuring the ambient atmospheric pressure. Since "vacuum" is the difference between atmospheric pressure and manifold absolute pressure, and is the best indicator of engine "load" (driver demand), the ECM needs both to measure "vacuum" effectively. That was added to the carb systems in 84. EFI generally doesn't need that because it goes about metering fuel in a different way.

The MAP sensor is identical appearing to the baro sensor, and is next to the fender, past the right edge of your red circle. Your new system won't have one "built in" since that's impossible; it'll have to have one compatible with it mounted somewhere, and exposed to manifold vacuum, either by being mounted directly into the intake like lots of LS motors do, or on the firewall or wherever with a line connecting it like many others do. It might even come with its own, I don't know, but it can't be "built in" regardless.

The odd shaped black can is the vacuum reservoir for the cruise and HVAC. It's needed because when you open the throttle, vacuum goes away; and without vacuum, the doors that steer the air under the dash and the cruise diaphragm, will all return to their "rest" position. So, there's a check valve, to only allow vacuum to flow in one direction (yeah I know, the idea of vacuum "flowing" is kinda ... yeah), which is, from the engine and toward the accessories; and the reservoir stores enough vacuum to supply the various systems' needs for awhile. So you'll need to keep that. It contains the check valve in question, so it's important which line is hooked up to it where; that is, the vacuum supply from the engine, and the loads.

Somewhere there's one of those hard plastic lines that goes from the reservoir to the HVAC control head. It's included in the HVAC wiring harness which comes through the firewall down by the transmission dipstick. Obviously you'll need to keep that as well.

 

Thank you! Big help! Sounds like I can eliminate the baro sensor but need the vacuum reservoir with the 2 lines connected to it (#1 hose from the intake manifold and #2 vacuum line for the HVAC operation). I just need to find another place to mount it. I'm still a little confused on the MAP sensor at this point. I will reach out to Holley and find out more details on the MAP sensor to find out what to do. I wonder if the hose with the brown end is from the MAP sensor? That would make sense. So, am I correct that the only reason I would need a MAP sensor is to be connected to the Sniper 2 EFI for it to operate properly, and it would need to be compatible with the Sniper 2 EFI system? So, I would need to use the stock one (if compatible) or purchase a compatible one to connect to the Sniper 2 EFI and replace the stock one? I can't thank you enough! You have been very helpful at clearing up this mess.

 

Yes. Every EFI system uses a MAP sensor.

Yes. It's not impossible that one comes with the system butt that would be a Holley question I suppose.

 

I just confirmed with Holley that the Sniper 2 has a MAP sensor built into it. So I will not be using the stock one.