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Old 10-21-2023, 08:48 PM   #172
MiniD
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Join Date: Mar 2007
Location: Portland, OR
Posts: 108
Re: 1973-1991 Dual fuel tank systems theory of operation

Quote:
Originally Posted by rodstored-72 View Post
hatzie, thank you for the reply, so do the contacts start/stop power to the motor and how can "a guy" check to verify the motor switched completely from one side to the other (not partially switched or in between the ports)?
the system in question is a LS swapped '86 c10 with '87 tanks, '87 sending units & EP381 F.P.s. the 12v signal is coming from the signal at the stock '13 ECM and harness.by chance does the motor require a timed amount of power to move completely? my F.P is low (50-55psi) and trying to verify the valve is not causing the lack of fuel.... ??

again appreciate your time and knowledge.. you are always very helpful on the board.
Don't use the standard tank selector valve with an LS setup. The selector valves are only rated up to 65 psi. You can use it for the return but the supply needs a different solution. I went with a straight T fitting from the tanks (each tank feed needs a check valve prior to the T).

The tank selector switch (EFI - which locks in position) will also toggle the power to your fuel pumps or fuel pump relays. This can decide which tank to pump from. You can still have the stock switching valve work for the return line routing (much lower pressure) and that way original wiring still works for the fuel guage.

<edit>since you said "FPs", I assumed you are referring to in tank fuel pumps. You can use the stock fuel tank switch if you're using a fuel pump up-stream</edit>
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1970 C20 SWB convert - 4.8l/4l60e
1985 C10 SWB

Last edited by MiniD; 10-21-2023 at 09:25 PM.
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