1983 GMC pickup fuel problem

[GrymReaper]

Okay, I've got a 1983 GMC High Sierra C2500. I let some friends borrow it to move and of course it magically breaks down. They claimed it just stopped, I'm pretty sure they ran it out of gas, but refilling it didn't help. When I got it I was warned not to switch the tank from right to left for some undisclosed reason, I imagine they ran out of gas, tried to switch tanks, and then something happened. I just don't know what.
I was able to start the truck by filling the float bowl, but there was still no gas to the carburetor from the fuel pump. A pressure test on the car led me to believe the fuel pump might be at fault, but after removing it and performing a bench test with a jar of gas and some hose it seems to pump fine. I'm not sure how accurate such a test is, but I digress.
I replaced the fuel tank selector switch, but no matter what tank is selected the gas gauge is pegged at 3 o'clock. Am I looking at bad sending units here or what? If so, is there any way to test for that without dropping the tanks? Cause if I drop the damn things I'd rather it be for a real good reason, as I can't exactly drive the thing around until it's empty. Let me know what y'all think. This is the first time I've had to play with a fuel system south of the carburetor, so I'm kinda winging it.

[68GMC454]

i would say the conpontents uder the bed are bad,,sorry dont know the name of them...but the piece that switches them,,,mine is plumbed straight into the left tank...

[benoit454]

As cheap as block mounted fuel pumps are you should just replace it.

I've bought several the last few years for different vehicls and for a small block chevy they are about $15.

Other then that, time to drop tanks, pull lines, make sure they are clear by blowing through them with compressed air, and make sure the sock on the bottom of the pickups isn't clogged up. I'd replace thoose too they are cheap.

Then you can find the best looking tank and plum straight into only that one and loose the other if ya want.

it be cheaper the replacing the selector valve and all that stuff I'd think.


This isn't such a great idea, but I've done it before lol, if you can find the main fuel feed line out of either tank, or just one going to the fuel pump, you can disconnect it, run a long piece of rubber fuel line down into a gas container, and try and start it up that way.

If it does start and run, the lines are free from there to the carb and the fuel pump is good. If it doesn't then change fuel pump and clean the lines out.

I did that on a 76 because the tank had lots of holes, I ran my line up between cab and bed and put the gas jug in the bed, out of harms way and any backfires.

[wedgemon]

This is from a post I made back in March...

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 a short is the switch problem. Mine was a metal screw through the doorsill into the dome light wiring - go figure.

Hope this helps!!

- Dave

[GrymReaper]

Originally Posted by wedgemon

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.

And the switch is that black doodad on the right frame, just in front of the right fuel tank, right? Haven't gone that far back yet, but I saw it.
So the fact that I was told upon receiving this truck to only use the right tank could be a good indicator of a bad switch? And if someone was to flip the selector switch in the cab, could it then cause the switch to not select either tank?

Originally Posted by wedgemon

You need to get some fuel in the right tank and see if it starts. Then, you need to determine if freezing or a short is the switch problem. Mine was a metal screw through the doorsill into the dome light wiring - go figure.

Oh, no, now I'm getting scared. This truck is a wiring nightmare. My grandpa gave it to me, and every time I crawl under it I find another magical wire that seemingly goes nowhere. Guess it's time to get me some wiring diagrams...

Originally Posted by benoit454

As cheap as block mounted fuel pumps are you should just replace it.

I've bought several the last few years for different vehicls and for a small block chevy they are about $15.

Other then that, time to drop tanks, pull lines, make sure they are clear by blowing through them with compressed air, and make sure the sock on the bottom of the pickups isn't clogged up. I'd replace thoose too they are cheap.

Then you can find the best looking tank and plum straight into only that one and loose the other if ya want.

it be cheaper the replacing the selector valve and all that stuff I'd think.

Sweet, I'm glad to hear the parts are cheap.

Thanks for the insight, guys, but I'm still curious as to why the gauges are pegged. Anyone know what exactly would cause that symptom? At this point I'm figuring that my problem is electrical in nature, mainly so I can exhaust all other possibilities before dropping the tanks.

[benoit454]

Well I remember someone telling me once that if the guage is pegged, that whatever was going on with it, and if it was bottomed out like on e that this was wrong, and if it was stuck in the middle something else was wrong.

I have no idea what they were now though.


Here's a little insight though, I had one with a broken or bad ground, it stayed on empty and would bounce around alot, when it did work.

Now I went through everything on my monte carlo, because after having the tank out for not getting any fuel I had the ground break off and I riveted it back on. Well after filling it up with some gas it went to half tank, and never moved again. I had it like that for a year, stuck on half tank. I checked everything, took the tank down and re-grounded it to be sure, turns out the fuse blew LOL. Boy did I feel stupid, but I swear when it first happened I checked the fuse. I guess not though because I changed it, and it's worked fine ever since.


So check your fuse first. if that's good then it's probably the ground or plugin. If you can get to them, unplug them and clean them, then plug em back in, if that don't work your guage might be screwed.

Sounds like they got the wrong ohms coming out of them or the guage broke, I say this because I got a temp switch for the old 86 k10 we had, well it had guages, and all they had was one for lights. I put it in, plugged the wire up to it and it stayed pegged past 250 all the time. Soon as I unplugged it, it dropped to the bottom left.

So again unplug them and see if the guage drops. If not guage might be shot.

[boxrodz]

Grym -
Sounds like you may have a fuel tank selector value issue. If it is working properly, you should be able to hear the solenoid inside the selector valve switchover when the fuel selector switch is depressed. Here's a wiring schematic for your '83.



If you are getting a 3 o'clock reading from the fuel gauge, then you have an open on the wiring (pink, pink/white and pink/black) between your gauge, the eletrical connector at the fuel tank selector valve, and the grounding point of the sending unit(s). Check to be sure that the ground wires for the sending units are grounded to the frame (located near the tanks). If the metering switch function of the fuel tank selector valve is also bad then this could also be causing the open connection and the past full reading. BTW, grounding the (pink) wire from the fuel guage should give you a 'E' reading.

[GrymReaper]

Yep, sure enough it was the fuel tank selector valve. I set up a simple circuit to bench test the solenoid and got nothing. Picked up a new one today ($113! Yikes!), plugged it in, and turned the ignition on. IMMEDIATELY get gauge readings from both tanks. Slapped it back together (those tank to valve fuel lines were a real pain to put back), poured a little fuel in the float bowl and fired it up. Runs like a charm now. At least I didn't have to drop the tanks. Thanks for the help, y'all!

[infinite-foamies]

Originally Posted by boxrodz

0V not -12V? I am using this valve on my 1971 K10 Suburban Cummins swap for my dual tank setup.

[chrismoore701]

Check your fuses

[infinite-foamies]

Originally Posted by chrismoore701

Check your fuses

Most helpful post ever.

[Auctioneerhere]

I cannot see what fuse is for the selector valve on my 84 w/ dual tanks.

Anyone have a clear picture link?