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'87 Gas Tank Switching Valve

Discussion in 'Chevy Trucks' started by 400hp408sb, Jun 16, 2002.

  1. 400hp408sb

    400hp408sb Junior Member
    from Maine
    Messages: 25

    Long story short. The truck came with a 350 TBI, now has a 400 with a carb. I took the computer out and it no longer switches to the 2nd tank. I know I can buy the carb version of the valve for about 70 bucks from GM dealer. Just curious how difficult this job would be and would I have to change the switch in my dash because of any wiring changes. And do both versions have the same amount of inlets/outlets to them? I'd love to hear your 2 cents. :D :D
     
  2. farmboy4

    farmboy4 Junior Member
    Messages: 9

    Wiring

    Assuming you have the original electric fuel pumps in the tank you have two options. Rip them out, replace with mechanical pump pickup tube in tank, and get a mechanical pump. The second option is rewiring (much easier). When you took out the computer you removed a hot (+) wire that came from the oil pressure sending unit this shut off power to the fuel pumps if oil pressure dropped. You should be getting no fuel right now, if you were you would be able to hear the fuel pumps whine. Near the middle quarter of the driver's side fire wall there is a small bundle of three wires this goes to your tank switch down to the fuel pump selenoid on the passenger side frame rail. There is a gray wire that controls the right tank fuel pump and a brown wire that controls the left fuel tank pump wich is energized by the switch, but the third wire is a tan and white wire that must be energized when the key is on. The tan and white wire was hot with the oil pressure sending unit. I have an 87 305 that i converted to carb. I completely removed all computer controls so if you have any further questions please email. Farmboy4@hotmail.com
     
  3. 400hp408sb

    400hp408sb Junior Member
    from Maine
    Messages: 25

    I guess I shouldn't have made my long story so short :) . Here's the deal. I'm running a holley mechanical pump on the engine. I left the electric fuel pumps in the tanks not running and the mechanical pump is just pulling through the electric ones. I want to be able to switch to my secondary tank. At the moment I am unable to do so since I took out the computer. As far as I know everything works fine. Been running it this way for a while now. I just really need that 2nd tank for camping/fishing trips. So my question is what is the easiest way to get this sucker to switch to 2nd tank without replacing the electric pump/sending unit with a carb version. Thank you for your replay Farm. Now I know which wires to look for when I eventually do the job.
     
  4. farmboy4

    farmboy4 Junior Member
    Messages: 9

    another route

    Another way to go about it is to take the fuel supply line and run it to the carb after the carb put in a fuel regulator to bring it down from 13 psi to about 5 or 6 psi. After the fuel regulator the line should go to your return line. Fuel regulators are as inexpensive as about $20 to $200. The reason for doing this is that your fuel pumps in your tank will become energized when you hook up that tan and white wire. When i converted mine i had a red wire outside the firewall at the fuse block that originally powered my EST (tbi distributor). I used this to power my new vacum advance distributor and my fuel pumps/switch.