Stumped.

[dvdswan]

78 K10, 350, 4sp, 205, dual tanks. I'm not getting fuel to carb. drivers tank is full, pass tank 2 gallons. I've had an intermittent stall issue since I bought the truck (its not my daily), didn't matter if it was hot/cold, dry/wet. It would happen only going up a hill just not all the time.

I've replaced both tank sender and clean out the tanks about a year ago, they were dirty, socks were brittle and really none existent and had junk in the tanks. replaced the switch valve when I bought the truck as it was bad. just replaced the mechanical fuel pump because there was no gas to the carb and replaced the fuel line to the carb as it was kinked and installed fuel hose with extra fuel filter. the carb has been rebuilt about 2 years ago and help performance and gas mileage.

I'm still not getting gas to the carb from either tank. now I'm stumped.

any suggestions?

 

[1987 GMC Jimmy]

What about the fuel lines at the tanks? How do they look? I’d put a fuel hose directly in a gas can at the pump to rule out the top of the fuel system. What about the switch valve? Did you replace it before or after you cleaned the tanks?

 

[dvdswan]

fuel lines I figured were large enough that crud wouldn't clog them but a piece large enough would block it. when I replaced the sending units and cleaned the tank I thought I had found the issue since they were filthy. It didn't stall for quite some time, at least a year. So I thought it was fixed. I didn't think of putting a gas can to the pump to eliminate the pump on.

the valve was replaced before I did the tanks. I did check the valve to see if it was switching, which it didn't so I swapped the lines and still got nothing.

so if there is a clog its either in the main line or the valve. is it possible that crud could keep the valve from switching? its old style, 2-in / 1-out single post.

 

[1987 GMC Jimmy]

Sorry, I should have been more specific. Were the lines cracked and dry rotted at all? They can suck in air like that and cause fuel starvation. And yes, I asked about the timeframe on the valve replacement because it’s possible for crud to wedge itself in there and cause problems. I would test this by bypassing the valve to the default tank and see if your issue clears up.

 

[Snoots]

is it possible that crud could keep the valve from switching? its old style, 2-in / 1-out single post.

Yes.
If it were me, I'd put more than 2 gallons in the passenger tank. You could disconnect the line at the fuel pump intake and pressurize (each) tank, switching the valve to get any trash out of that line.

Hopefully, there is no trash in the pump. Do you have an in-line filter before the pump?

 

[dvdswan]

Sorry, I should have been more specific. Were the lines cracked and dry rotted at all? They can suck in air like that and cause fuel starvation. And yes, I asked about the timeframe on the valve replacement because it’s possible for crud to wedge itself in there and cause problems. I would test this by bypassing the valve to the default tank and see if your issue clears up.

I replaced all the rubber lines when I dropped the tanks. The lines were the original ones from what I could tell (still had the original undercoating on them) but didn't have cracks from what I remember.

Yes.
If it were me, I'd put more than 2 gallons in the passenger tank. You could disconnect the line at the fuel pump intake and pressurize (each) tank, switching the valve to get any trash out of that line.

Hopefully, there is no trash in the pump. Do you have an in-line filter before the pump?

no, I placed the filter after the pump. should I place it before the pump? I'll try the pressurizing, but if it is clogged wouldn't that blow the crud into the socks on the sending units? would it be ok to pressurize with the feeds from the tanks disconnected at the switching valve?

 

[78C10BigTen]

On my 78 when i got it it wouldnt get gas either, what i did was take the line off at the pump and use a blow gun on the air compressor and blow air down it to the tank till i heard it rumble in the tank. Many will say its not good because it turns up all the crap at the bottom of the tank but it worked like a charm. The line started shovin gas so i stuck it back on and it worked good.

 

[Snoots]

no, I placed the filter after the pump. should I place it before the pump?

I've got one at both ends/sides.

 

[1987 GMC Jimmy]

On my 78 when i got it it wouldnt get gas either, what i did was take the line off at the pump and use a blow gun on the air compressor and blow air down it to the tank till i heard it rumble in the tank. Many will say its not good because it turns up all the crap at the bottom of the tank but it worked like a charm. The line started shovin gas so i stuck it back on and it worked good.

I've done this to check for obstruction except with my mouth. Your way is a lot better.

 

[78C10BigTen]

I've done this to check for obstruction except with my mouth. Your way is a lot better.

Ive seen my dad do this to many fuel systems on like lawn mowers and such but i figured i couldnt make enough pressure on the truck so i thought hey wtf use the air hose.

 

[1987 GMC Jimmy]

I did it on a 35' motorhome so it does work on the big stuff, but I had to have another person at the tank listening for gurgling.

 

[dvdswan]

Well, I pressurized the intake line at the pump and could hear and feel the driver's side tank air at the filler neck. When I switched to the passenger side tank it still came out the driver's side (heard and felt). So apparently I hooked the tanks up wrong when I installed the switching valve way back then. Plus the valve seems to be bad, I took it off and tested it. no click heard when I applied 12v to it, it was grounded as well. I will have to pick up another valve.

I think I'm going to look at the selector switch as well, because it shows the left is full but I didn't hear any bubbles. I bet the left is completely empty and why its not getting any fuel. Poor trouble shooting on my part I hope.

 

[dvdswan]

So... I had a brain fart. Left tank was empty, put 2 gallons in it, truck fired up. I swapped the lead at the selector switch so the proper tanks read right on the gas gauge. Now I need to fix the ground on the left tank as it reads past full.

Also, swapped the water pump as the bearing was bad. Truck runs now with no bearing whine and doesn't loose any coolant either. Selector valve will be here tomorrow and I can start driving it daily again.