Dual tank fuel gauge makes no sense.

[mtbadbob]

My only problem is that when my right tank gets below 1/4 full, my truck will periodically die, like the pump loses pressure or prime. It'll immediately start back up, but it's kind of dangerous & annoying as I'm usually slowing down to turn or stop when it does this. I guess I may have to pull my tank and investigate why, or replace the new pump I had just installed this past summer.

 

[SirRobyn0]

My truck does not have the rocker switch, and my fuel gauge reads correctly on each tank. I was merely informing JM of KY on the status of my '87 TBI set-up as I thought he suggested that the newer switches were the rocker-type, which mine isn't. My switch is the correct one that stays depressed on the selected tank. As you know, the switches will not interchange with the different factory harness plugs as there is an odd pin on the back of the switch to prevent that from happening. If you look them up on NapaOnline, you can view both types of switches & see the difference in the switch pins/terminals.

Right. Sorry about that, I was apparently confused on who was having the issue needing help. I do apologize for that.

 

[SirRobyn0]

My only problem is that when my right tank gets below 1/4 full, my truck will periodically die, like the pump loses pressure or prime. It'll immediately start back up, but it's kind of dangerous & annoying as I'm usually slowing down to turn or stop when it does this. I guess I may have to pull my tank and investigate why, or replace the new pump I had just installed this past summer.

I can sort of relate. My truck is carbureted so I'm drawing from the tank. It was originally a single tank truck, when I bought it I was not happy with number of miles I could travel before needing to fill up, when I was loaded or more over if I was towing my trailer. So installed a second saddle tank. Now I'm not the kind of guy that likes to run his gas tank to low, I typically like to leave a 1/4 tank buffer, but I have a method to get the most miles out of the two tanks. Fill them both, run the left one until it's empty, as in hammered on E then run the right down to a 1/4 and refill. Well there have been a few times when I've been less than mindful how long I've driven on the left tank very low and ran it out. I've got a good strong fuel pump it didn't take to much cranking to get it going again, but yea I understand the feeling you are describing.

 

[JM in KY]

Just to close the loop here:

To review, my truck would show me the fuel level in the left tank only, regardless of which tank was selected. The switch inside the cab correctly switched the fuel pumps, which I verified while the truck was running and by accessing the testing wire in the relay at the top of the firewall.

I played around with this for a couple weeks. Didn’t want to accept that the new fuel selector valve I put in would be the problem.

Well, turns out the brand new AC Delco selector valve WAS the problem. I unplugged the weatherpak connection and just jumped the wires that lead to the gauge. I could make it go to empty or full on either circuit leading to the gauge. This told me the wires leading to the gauge should be able to correctly display the fuel level for either tank.

So, I put in a second brand new fuel selector valve and now everything works fine.

 

[SirRobyn0]

Just to close the loop here:

To review, my truck would show me the fuel level in the left tank only, regardless of which tank was selected. The switch inside the cab correctly switched the fuel pumps, which I verified while the truck was running and by accessing the testing wire in the relay at the top of the firewall.

I played around with this for a couple weeks. Didn’t want to accept that the new fuel selector valve I put in would be the problem.

Well, turns out the brand new AC Delco selector valve WAS the problem. I unplugged the weatherpak connection and just jumped the wires that lead to the gauge. I could make it go to empty or full on either circuit leading to the gauge. This told me the wires leading to the gauge should be able to correctly display the fuel level for either tank.

So, I put in a second brand new fuel selector valve and now everything works fine.

I get it, sometimes it's hard to think a new part is bad, and from companies generally trusted like ACDelco, it's harder, but still happens. Glad you have a functional gauge again!

 

[Dleslie212]

I did an EFI conversion on my '77 and don't have any issues with the fuel level based on the selected tank. Take a look at https://www.gmsquarebody.com/threads/tank-replacement-for-efi.24131/page-2#post-472294 which shows the parts list I used. I agree with others that it is most likely incorrect wiring or a bad selector valve or sending unit.

I actually used your thread pretty extensively when I converted my 77 last year, so thanks for that

 

[gogo14910]

This diagram helped me connect the correct fuel sending unit when I deleted the selector valve and passenger tank. It’s in my thread, “help! tank delete”.