76 C10 Dual Tank Questions

[datmony]

I have a 76 C10 pickup. I am running into a strange issue that has recently started. If I am running the truck on the driver's side tank, it will periodically start to stall. It feels as though it is running out of gas when this happens but there is still plenty of fuel in the tank.

When this happened the first time it would not start at all after it died. I did not know what the issue was and had just swapped in a GM performance crate motor three days before so I automatically thought it was an issue with the install. I had it flat bedded back to the shop and it started immediately. It was then driven for over a hundred miles and I could not reproduce the issue.

The other night the issue started again. This time I switched to the passengers side tank and the issue went away. I switched back to the driver's side tank and the issue was back.

My immediate assumption was that it was something in the tank that was clogging the line out but through some additional conversations I am wondering if it might be something more than that. With those dual tank set ups is there some sort of a pump in the tank that is potentially going out? Not sure if there is a sump of some sort in the tank that could be going out or if the valve that controls which tank is being used could potentially be going bad and cause symptoms like this?

Just want to get some additional insight since I am going to have to drop the tank anyways. If there is a decent potential that it could be one of these other things then I figured it is just easier to replace all those parts while the tank is out.

Thanks in advance and let me just say how exicted I am to find this message board. I have been looking for one that is GM specific and finding resources online specific for these trucks is vey tough.

[wedgemon]

This sounds familiar...

I'm guessing the "assumed" full tank was the left one. And nothing happened when you switched to it. Correct? Dual tanks DEFAULT to the right or passenger side tank when the switch valve freezes or faults (electrical short). The gauge still will reflect the tank as full, but switch over never happens - and you run out of gas on the right side tank.

This exact situation happened to me 2 years ago. And cost me almost $300 to diagnose.

You need to get some fuel in the right tank and see if it starts. Then, you need to determine if freezing or short is the switch problem.

Hope this helps!!

- Dave

[benoit454]

I too would think something in the tank was plugged up. Might not hurt to drop it, pull the unit, change the socks and check for crap in the tank. ESP> if you don't have hardly any fuel in it now.

[boxrodz]

I had a similar problem a few years back on the '83.

Every once in a while it would choke as I stepped on it. It seems like it was not getting enough fuel when you step into it. Years ago, my Dad had a similar problem on his '73 and it turned out to be a clogged fuel filter. So, as it became more frequent, I changed out the fuel filter and while I was at it, the fuel pump. Then a few months later, it would start up again. I replaced the fuel pump again and thought the issue went away. Then, on a long trip, it occurred again but just slightly. However, on the way back it started up again everytime I stepped into it. I had just driven through the city and was headed up the Divide when I finally decided to pull off the Interstate and onto a side road. After retreiving another fuel pump and some tools (tough to do on a Sunday evening), I reinstalled it with the help of the headlights of the local police. As I replace the fuel pump, the officers were busy checking out the truck. One of them said, they wanted a truck just like it. The other said it was nice, but ... it really wasn't a truck since it had carpet. All along, they questioned whether I was going to be able to get it back on the Interstate. After a few minutes, I was back on the Interstate and did make it back to my destination, thanks in part to the two officers.

A few weeks later it started to occur again. I inspected the whole fuel system, but this time I found out that if the fuel selector switch was set to the primary (driver side) tank, the fuel selector valve would slightly leak. When the valve was set to the auxillary (passenger side) tank, the valve would not leak. I suspect that while I was driving using fuel from the primary tank, the fuel pump would pull in more air than fuel from the leaking valve whenever I stepped into it. Since it didn't leak when using the auxillary tank, I didn't have any problems. I replaced the 6-port fuel selector valve and have not had any more problems, including during a two-state trip.

I'm not aware of any in-tank pump. But, since you're dropping the tank, I would check to see whether or not the pick-up or other lines are clogged. If the lines are clear, set the selector valve to the primary tank and see if it leaks fuel (usually noticeable when the truck is sitting after a drive). It just may be the valve especially if it's the original one. But, as wedgemon suggested you may also want to inspect the fuel selector switch.

[dacanuck]

I have a similar problem with my dual tanked truck... Sometimes it will not idle and I have to keep my foot on the gas to keep it running, but it runs okay at high rpm. my co-worker (we're both professional heavy equipment technicians) thinks I have an air leak in my fuel system. On top of that my truck won't switch between tanks anymore. Is it worth keeping the dual tank setup or better to go with one, or even a fuel cell in back?

[porpaintt]

I had those problems and stopped them by(heaven forbid)putting a ford valve up front and eliminating the chevy valve. It has not given me a problem in 20 years.The ford valve is simple and only uses power one way

[shadetree]

Excellent thread! I've had some issues with my 84 dual tank, and this thread gives me a lot of insight. Thanks, guys

[andrist1]

I had the same situation arise on my 75' last year, and it ended up being the switching valve. The valve was stuck open between the two tanks and was sucking fuel out of both tanks. In my case it was open more to the passenger side so the gauge read the passenger tank. I replaced the valve and all was back to working as normal.

[Yankeelights]

Originally Posted by wedgemon

This sounds familiar...

I'm guessing the "assumed" full tank was the left one. And nothing happened when you switched to it. Correct? Dual tanks DEFAULT to the right or passenger side tank when the switch valve freezes or faults (electrical short). The gauge still will reflect the tank as full, but switch over never happens - and you run out of gas on the right side tank.

This exact situation happened to me 2 years ago. And cost me almost $300 to diagnose.

You need to get some fuel in the right tank and see if it starts. Then, you need to determine if freezing or short is the switch problem.

Hope this helps!!

- Dave

Does the tank valve default to the right on a 79 also?

~ Dave

[wedgemon]

Originally Posted by Yankeelights

Does the tank valve default to the right on a 79 also?

~ Dave

Yes.

- Dave

[Yankeelights]

Thank you ... problem fixed ... firewall harness was unplugged.

~ Dave