Gas Delivery Problem

[Cris]

I have a very stock 63 C10 with a 230 inline six. It runs perfect until the gas tank gets below 1/4 tank. Then, many times, it will not start. Especially if the truck has been sitting for a week or two. The fix is always the same. Cup my hands around the fuel filler neck and blow (pressurize the tank) for a few seconds and/or add some fuel directly down the carb.

I am guessing the fuel pump (stock mechanical) is dry and cannot suck gas in without some help. If the tank is full enough, this is never an issue presumably because the gas is higher in the tank (behind seat tank) and gives enough pressure.

Anyone dealt with this before? I'm getting tired of giving my truck a blow job to get started........

Thanks, Cris

[Clyde65]

Sounds like a fuel pump, also check the rubber hoses for collapsing

[Cris]

Fuel pump is good (new and checked for operation). I'll check the hose next time this happens. It is a new hose from the hard line to the fuel pump.

Does anyone have a photo of the routing of the hose from the hard line to the fuel pump on a 230 I6? Mine comes up and over to the pump, but not sure that is correct.

Thanks, Cris

[oem4me]

Seems unlikely that the small amount of pressure you can add with your lungs would be enough to do the trick. Perhaps the fuel cap is not venting correctly and it's merely cracking the seal and breaking the vacuum that gets it going again?

[Cris]

OEM:

I actually drilled a small hole in the cap to vent pressure.

The pick up on the in-cab tank is at the bottom, but then the hose goes up, exits the tank, then back down and heads to the engine and fuel pump. It almost seems an air pocket gets in there that the pump cannot overcome when the fuel level is low. The pump can't get the line "siphoning".

Crazy that I would be the only one with this issue. I must have something unique.

Tlhanks, Cris

[demian5]

Pull that sending unit and visually inspect it before throwing anymore parts at it.

[oem4me]

Originally Posted by Cris

OEM:

It almost seems an air pocket gets in there that the pump cannot overcome when the fuel level is low. The pump can't get the line "siphoning".

This makes perfect sense. Perhaps the pickup tube is compromised and draws air when the fuel drops below that level.

['63GENIII]

Hey Cris, might take a flashlight and see if you can see down to the bottom of the tank from the filler hole. Either that or pull the sending unit / pickup (when the tank is low). It should be silver and clean at the bottom.

Many times over the years these trucks are left with caps off or are left with a rag stuffed in them which lets rain water in. Water ends up rusting the tank. Rust plugs the brass sock on the end of the pickup. Worth a look. When I got mine, i could drive for miles on anything over a 1/2 tank. Any lower and there wasn't enough sloshing to keep the rust sediment off of the sock.

Also check the compression connection from the pickup line that's outside of the tank to the one that runs to the pump. You could be losing the prime there even if its not leaking fuel, the low tank level could siphon the fuel back into the tank from that point.

One last thing to check. IIRC, the sending unit is spot welded to the pickup at maybe 1/3 - 1/2 way up the tube. If one of those spot welds cracked, there may be a pinhole in the pickup. Like using a broken straw to drink a soda.

Good luck and let us know what you find.

[Nappers]

63GenIII, that's a good thought, answer if you will.

My best friend had a 63 GMC and it would vapor lock constantly, especially on hot days.

[Cris]

Guys, thanks. Some good ideas. Once the truck is "primed" it will run smoothly down to the last drop in the tank. The PO had replaced the tank and sender. I've had them both out of the truck, but never took a close look at the pick-up tube for cracks or issues. (I did have to replace a leaky float.)

Yesterday I had to "prime" the truck. It had been sitting for roughly two weeks without starting and is down to 1/4 tank. This morning, after sitting a day, it fired right up.

If it was a daily driver I would never see the issue.....

Thanks, Cris

[luvbowties]

Originally Posted by Cris

Guys, thanks. Some good ideas. Once the truck is "primed" it will run smoothly down to the last drop in the tank. The PO had replaced the tank and sender. I've had them both out of the truck, but never took a close look at the pick-up tube for cracks or issues. (I did have to replace a leaky float.)

Yesterday I had to "prime" the truck. It had been sitting for roughly two weeks without starting and is down to 1/4 tank. This morning, after sitting a day, it fired right up.

If it was a daily driver I would never see the issue.....

Thanks, Cris

Chris, is there a choke whose flap is closing completely when cold?

HTH,
Sam

[heavy71chevy]

It sounds like the screen is plugged..that's why blowing into it helps.an electric pump would solve this most likely but I'd flush the tank because ethanol fuel can cause this from sitting for any amount of time cause the green build up aswell

[Cris]

Sam:

Its a manual choke and it does completely close if you pull it all the way out. I live in California so the engine never really gets that cold. My typical starting procedure is full choke till it fires then immediately to half choke.

Thanks, Cris

[Cris]

Heavy:

Tank is new and is checked. Pick up is new and checked (except for cracking).

I guess it also could be the fitting from the tank to the hardline. I have had a heck of a time getting that sealed.

I'll do some trouble shooting the next time it happens. Surprised that I am the only one with this issue!

Thanks, Cris

[mattfranklin]

I have this issue, too, with my '70 C10. Putting a mighty-Vac on the fuel line kind of worked, too. The pump is new and probably has fewer then ten hours on it. Sometimes I even fill the fuel bowl and get it running great for 15-20 seconds. Multiple times in a row. I thought I solved the problem with I went through the carb and removed some water/ethanol corrosion, but that might have just been giving it enough attention to get it primed. I think I have better luck with priming when I park the nose downhill, but I've not yet done a thorough study of what works and what doesn't.

Did you ever work out a solution?

[AcampoDave]

Not only pressurized fuel lines can cause fuel delivery issues. A crack in the line between the tank and pump can cause a problem too because it will vent the line. Like drinking a big gulp with a cracked straw. You can do it but it's not smooth. Edit: some of it could be normal too because after a couple of weeks of sitting around in the heat my carb dries out and I gotta do the ol' pump the throttle till my foot gets tired while I crank the motor.

[bsarts]

You have a pinhole or a loose clamp in the hose under the tank that slowly lets a little air in over the course of a couple weeks and drains the standpipe. Or maybe even a crack or hole in the hardline going from the tank down through the floor. Also check the tightness of that connection - hardline to sender.