1987 Dual Tank Problems

[Low69CST]

I'm about to start diagnosing why the passenger side tank quit working on my truck. Does anyone have some tips or common problems. When you hit the switch the truck immediately shuts off. Just like you turned the key. I'm thinking it's the switch or the pump. Any ideas are much appreciated.

Marshall

[Chrispbrown36]

Could be sending unit or pump. Mine didn't work when I bought it. Dropped the tank and pulled everything out. It was all rusted out inside the tank. Eventually I am going to replace the sending unit, pump, and tank. For now I am running off of one tank.

[gmachinz]

Originally Posted by Chrispbrown36

Could be sending unit or pump. Mine didn't work when I bought it. Dropped the tank and pulled everything out. It was all rusted out inside the tank. Eventually I am going to replace the sending unit, pump, and tank. For now I am running off of one tank.

Yep-rust is very common to find.

[nickvig]

Originally Posted by Low69CST

I'm about to start diagnosing why the passenger side tank quit working on my truck. Does anyone have some tips or common problems. When you hit the switch the truck immediately shuts off. Just like you turned the key. I'm thinking it's the switch or the pump. Any ideas are much appreciated.

Marshall

I bought my truck from a guy in April. Six months before he sold the truck to me he had the passenger side tank replaced, as well as the valve, and switch. Everything worked perfectly up until about two weeks ago. I have the same problem as you, flip the switch and the truck dies.

I've been doing a lot of research here to see how to diagnose it. If you search a bit you'll find a thread where Hatzie explains how to diagnose the whole thing. You'll need a test light and someone to help you as you check the various wiring from the switch and at the valve.

Here's what I noticed on mine. When it quit working the fuel gauge no longer reads the passenger side tank. When you flip the switch you can hear both fuel pumps after you shut off the truck but I don't get any reading for fuel. So in my case it's probably bad wiring somewhere or a bad valve. Unfortunately when mine was replaced they used a non-OEM valve so I think that might be the issue. I've already got an AC Delco replacement but I haven't had the time to swap it out.

[nickvig]

Here's the thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=567277

[gmachinz]

Originally Posted by nickvig

I bought my truck from a guy in April. Six months before he sold the truck to me he had the passenger side tank replaced, as well as the valve, and switch. Everything worked perfectly up until about two weeks ago. I have the same problem as you, flip the switch and the truck dies.

I've been doing a lot of research here to see how to diagnose it. If you search a bit you'll find a thread where Hatzie explains how to diagnose the whole thing. You'll need a test light and someone to help you as you check the various wiring from the switch and at the valve.

Here's what I noticed on mine. When it quit working the fuel gauge no longer reads the passenger side tank. When you flip the switch you can hear both fuel pumps after you shut off the truck but I don't get any reading for fuel. So in my case it's probably bad wiring somewhere or a bad valve. Unfortunately when mine was replaced they used a non-OEM valve so I think that might be the issue. I've already got an AC Delco replacement but I haven't had the time to swap it out.

If it's the 6-wire valve, there are two limit switches which alternate contact as the worm gear contact drive moves to LH or RH tanks-this is where the reading for fuel level comes from. On sending units with a lot of use, sometimes the arm which makes contact with the sender assembly gets warped which causes it to not read correctly-simply bending the arm "slightly" towards the sender will correct this. GM senders are 90-ohm and my OEM ones measured 0-83 ohms from full travel to empty. You can test your senders be setting your multi-meter to ohms and probing the sender stud with one lead and probe the metal sender body with the other. Now, slowly move the arm back/forth and the resistance should change.

If you have the single wire solenoid valve, keep in mind for it to switch properly, it must have a good frame ground to operate. The body of it is grounded by being bolted to the frame so make sure your frame to grounded well to the battery.

[Low69CST]

Thanks for the information. It was very helpful. I figured out that the selector valve was getting power when the switch was flipped to LH and RH. I also figured out that each fuel pump in the tanks were getting power. Also, we took the fuel pump out of the tank that wasn't working and verified it worked by hot wiring it. So i'm guessing the tank selector valve is bad and ordered an AC Delco replacement from Rock Auto. We are also getting new sending units from a local parts store. The driver's side had rusted through and was leaking (which is what caused us to finally start working on it). While the fuel tanks are off, we are also putting in new rocker, cab corners, and front inner fenderwells.