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02-28-2020, 01:59 PM | #11 | |
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Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,927
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Re: 1973-1991 Dual fuel tank systems theory of operation
Quote:
The TBI trucks also use the power wire from the dash switch to energize the selected fuel pump. One of the output wires is power and the other is ground and the polarity changes based on the switch position. If you select the LH tank and the valve doesn't move the RH fuel pump still shuts off and the LH fuel pump still turns on... as long as the wiring hasn't been tampered with. The engine keeps running so I have to assume the switch and valve are changing tanks and fuel pumps. This leaves the little microswitch inside the valve that handles the gauge. If the gauge microswitch inside the valve on terminals A B & C has failed but the rest of the valve is working it would exhibit your list of symptoms. Get a valve made by Pollack and be done with it. I believe the latest and greatest good to 65psi is Pollack 42-159P. They aren't cheap but they work for a long long long time.
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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. Last edited by hatzie; 02-28-2020 at 02:16 PM. |
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