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#1 |
Moderator
![]() Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,927
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Re: 1973-1991 Dual fuel tank systems theory of operation
Each fuel pump gets power from the polarity reversing switch and ground from the frame.
The fuel gauge sender select switch is in the valve. There's no reason the gauge switch couldn't fail in one position or the other and the valve itself still route fuel correctly. Try this;
If the senders are both working and the tanks are at different fill levels the gauge should read different levels in 5 & 6. If your tanks are filled to the same level then the gauge will read the same in 5 & 6. Steps 1-4 are a sanity check to make sure the fuel gauge and the associated wiring is in proper calibration. This is a bitmap of a curve I plotted in Excel based on squarebody fuel gauge needle position vs a calibrated decade resistance box in place of a GM sender on my bench. ![]()
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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