Tank sending units - The 1947 - Present Chevrolet & GMC Truck Message Board Network

akart · 10-05-2019, 04:03 PM

I am gathering parts to replace my entire fuel system tanks,tank sensors.switching valve and dash switch. I have an '86 body and a '74 frame. the switching valve is a 6 port so I bought one of those ACDelco U7001 and 1 tank sensing unit ACDelco FLS 1001 from Summit which is the only AC one they list. Question: I see on Amazon there is a FLS 1002 which they say is for an auxilery tank. What's w/that? Would the FLS 1001 work on either tank? Also am getting the ACDelco D7089C switch which is recommended and it supposed to plug right in the existing wiring. The truck now is on the passenger side default tank,gauge works. Me thinks I have shorted a green wire to the manifold and maybe smoked the switching valve. I did replace the dash switch with another like one which has the Depress Fully printed on the bottom,no change.I just changed heads and cam and can do stuff like that but I find this fuel electrical a little complicated for me.
A little feed back please,Thank you.

kipps · 10-05-2019, 04:45 PM

The fuel sending units are not interchangeable, or at least aren't intended to be. When installed into older carbureted tanks with no baffles, they might be interchangeable. In a TBI tank, the sending unit won't set in the basket correctly. Also, the external lines are longer on the passenger side, for some reason.

GM called one tank the primary, and the other tank the auxiliary. To confuse things, it appears that GM changed which tank was the designated primary in the late 70's.

Regardless, if you order one of each sending unit, you should have a set.

**hatzie** · 10-05-2019, 06:23 PM

The DEPRESS FULLY switch is a momentary contact switch that springs back to OFF as soon as you let go of the switch.
I can't see how you could damage the motor in the valve.
It's a DC motor that spins different directions based on the polarity of terminals D & E.

The Dual Tank Theory of operation writeup may help clear things up for you. You have the 81-91 system in post #2.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061

Dleslie212 · 10-07-2019, 09:16 AM

Quote:

Originally Posted by hatzie

The DEPRESS FULLY switch is a momentary contact switch that springs back to OFF as soon as you let go of the switch.
I can't see how you could damage the motor in the valve.
It's a DC motor that spins different directions based on the polarity of terminals D & E.

The Dual Tank Theory of operation writeup may help clear things up for you. You have the 81-91 system in post #2.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061

Is there any harm in using a different switch? I just redid my entire fuel system, converting from the old style selector valve to the new style. But the switch i used has no OFF position, it’s ON-ON. I’m guessing the difference is that instead of the new valve only being powered for a second or so during switching, my valve is always getting power. Is that a bad thing?

**hatzie** · 10-08-2019, 07:51 AM

You can use the 87-91 TBI switch I mentioned in the theory of operation thread.
Some of them have the locator lump on a different terminal than the Momentary switch so you'll need to modify the plastic connector shell for the locator lump on the TBI switch terminal.

10-05-2019, 04:03 PM	#1
akart Registered User Join Date: Sep 2014 Location: Manley Hot Springs Alaska Posts: 253	Tank sending units I am gathering parts to replace my entire fuel system tanks,tank sensors.switching valve and dash switch. I have an '86 body and a '74 frame. the switching valve is a 6 port so I bought one of those ACDelco U7001 and 1 tank sensing unit ACDelco FLS 1001 from Summit which is the only AC one they list. Question: I see on Amazon there is a FLS 1002 which they say is for an auxilery tank. What's w/that? Would the FLS 1001 work on either tank? Also am getting the ACDelco D7089C switch which is recommended and it supposed to plug right in the existing wiring. The truck now is on the passenger side default tank,gauge works. Me thinks I have shorted a green wire to the manifold and maybe smoked the switching valve. I did replace the dash switch with another like one which has the Depress Fully printed on the bottom,no change.I just changed heads and cam and can do stuff like that but I find this fuel electrical a little complicated for me. A little feed back please,Thank you.

10-05-2019, 06:23 PM	#3
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Tank sending units The DEPRESS FULLY switch is a momentary contact switch that springs back to OFF as soon as you let go of the switch. I can't see how you could damage the motor in the valve. It's a DC motor that spins different directions based on the polarity of terminals D & E. The Dual Tank Theory of operation writeup may help clear things up for you. You have the 81-91 system in post #2. http://67-72chevytrucks.com/vboard/s...d.php?t=754061 __________________ 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... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

10-08-2019, 07:51 AM	#5
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Tank sending units You can use the 87-91 TBI switch I mentioned in the theory of operation thread. Some of them have the locator lump on a different terminal than the Momentary switch so you'll need to modify the plastic connector shell for the locator lump on the TBI switch terminal. __________________ 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... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

10-05-2019, 04:45 PM	#2
kipps Registered User Join Date: Jul 2014 Location: North-central Virginia Posts: 1,104	Re: Tank sending units The fuel sending units are not interchangeable, or at least aren't intended to be. When installed into older carbureted tanks with no baffles, they might be interchangeable. In a TBI tank, the sending unit won't set in the basket correctly. Also, the external lines are longer on the passenger side, for some reason. GM called one tank the primary, and the other tank the auxiliary. To confuse things, it appears that GM changed which tank was the designated primary in the late 70's. Regardless, if you order one of each sending unit, you should have a set. __________________ 1987 C6P V20 truck, 2010 LMG 5.3, AFM delete, 2010 Camaro exhaust manifolds, 1997 nv4500, 1991 np241c, hydroboost, 2005 14bff axle & driveshaft, drop-n-lock gooseneck, 4.10 gears, stock suspension, rims, and tires. Still a work in progress. Any questions or suggestions are welcome!



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