Close



Results 1 to 12 of 12
  1. #1

    Default What is this thing - 85 GT

    Hello All,

    My son and I are making an effort to clean up the engine bay a bit. Wondering what this part is and whether it can be deleted.

    It is near the firewall on the passenger side fender.Name:  85 GT Mystery Part re-sized.jpg
Views: 300
Size:  205.5 KB

    Thanks in advance!

    BG

  2. #2
    FEP Power Member qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,242

    Default

    Those are vacuum control switches. I'm pretty sure the ones on the passenger side on an '85 control the high altitude compensation solenoids in the pass side inner fender. They lean the mixture when the vehicle goes rich in higher altitudes. It works in conjunction with a funky barometric pressure sensor mounted to the front of the drivers shock tower.

    You can see what the solenoids inside the fender look like in the thread below.

    http://vb.foureyedpride.com/showthre...tion&p=1860738
    '85 GT

  3. #3

    Default

    Quote Originally Posted by qikgts View Post
    They lean the mixture when the vehicle goes rich in higher altitudes.

    http://vb.foureyedpride.com/showthre...tion&p=1860738
    On a Carbureted car?
    They are probably part of the pollution system tad/tab solenoids which are activated by a Thermactor dump control relay under your dash.....
    Also might be part of the manifold vacuum switch ( one on my 83 is on the backside of the drivers shock tower) which connects to the same under dash relay
    Cannot say for sure, but that is how my 83-302 car works.... A nightmare of vacuum and electric relays and solenoids.....
    The WOT switch ( which is on the carb where the throttle linkage bolts to it) is also involved with this system which ties in with another relay under the dash called the WOT A/C cutout relay....

  4. #4

    Default

    Quote Originally Posted by qikgts View Post
    Those are vacuum control switches. I'm pretty sure the ones on the passenger side on an '85 control the high altitude compensation solenoids in the pass side inner fender. They lean the mixture when the vehicle goes rich in higher altitudes. It works in conjunction with a funky barometric pressure sensor mounted to the front of the drivers shock tower.

    You can see what the solenoids inside the fender look like in the thread below.


    http://vb.foureyedpride.com/showthre...tion&p=1860738

    This is correct.

  5. #5
    FEP Power Member qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,242

    Default

    Quote Originally Posted by Bentley View Post
    On a Carbureted car?
    Yes, carbed car.
    '85 GT

  6. #6

    Default

    Quote Originally Posted by qikgts View Post
    Yes, carbed car.
    Can you tell me how that leans or richens a Carburetor??

  7. #7

    Default

    Quote Originally Posted by Bentley View Post
    Can you tell me how that leans or richens a Carburetor??
    Pretty interesting to learn about actually, I did a lot of research when I was trying to figure out the vacuum diagrams for the 1985 GT I am working on. Basically those vacuum switches work with the barometric pressure switch and a mess of vacuum lines, vacuum restrictors and solenoids that are mounted under the passenger fender. The barometric switch on the driver side strut tower is normally closed below 4000 feet, and the vacuum switches on the passenger side are also normally closed. The barometric switch opens above 4000 feet, and then the first vacuum switch opens above 5 inches of vacuum and the other above 10 inches of vacuum. Those switches send an electrical signal to the solenoid valves witch provide an air bleed (basically a slight vacuum leak) to the carburetor, and lean it out to provide better operation at high altitudes.

    I have a discussion of this topic on the General Tech forum of this site. In the first diagram of that post the solenoids and restrictions are shown in red on the lower right side.

  8. #8
    FEP Power Member qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,242

    Default

    Keep in mind, that series of components is not doing anything physical to the carb to change the afr's, it's leaning the mixture in the intake manifold by allowing more air in through a vacuum port.
    '85 GT

  9. #9

    Default

    Quote Originally Posted by qikgts View Post
    Keep in mind, that series of components is not doing anything physical to the carb to change the afr's, it's leaning the mixture in the intake manifold by allowing more air in through a vacuum port.
    Thank you for the explanation....

  10. #10
    FEP Power Member qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,242

    Default

    Quote Originally Posted by Bentley View Post
    Thank you for the explanation....
    Happy to help.
    '85 GT

  11. #11

    Default

    Qikgts - if this car is a street car / daily driver and will never see an altitude higher than MAYBE 2500', can all that stuff be removed?

  12. #12
    FEP Power Member qikgts's Avatar
    Join Date
    Jan 2010
    Location
    Rockledge, FL
    Posts
    1,242

    Default

    Sent ya PM, Sir.

    My short answer is: The carb won't care and I doubt it would change the actual performance. If anyone ever tested it a/b I'd love to know.
    '85 GT

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •