Starving for Fuel!?!?

[dfaulk]

Hey guys, I read post from here all the time but this is the first time posting.
I have a problem that even my mechanic can't figure out. I have a 1986 Silverado, 305 Quadrajet carb, basically all original. I can be driving down the road and the truck will die, starving for fuel. We replaced the fuel pump, tank selector (not the switch the actual valve), the connecting rod for the fuel pump and even got an electric fuel pump thinking that maybe the cam that pushes the connecting rod for the fuel pump might be so far gone that the mechanical fuel pump wasn't working. When it dies i disconnect the fuel line feeding the carb, there is no fuel flowing, but after turning the engine over a few times it starts pumping again and I'm back on the road again, for a while anyway. Any suggestion?? Thanks in advanced for anything you can offer.

SF

 

[Arkansas_V8]

Tank dirty? When it stops sucking it drops all the crud and you start over?

 

[dfaulk]

Fuel filter looks good, I guess it could be that.

 

[Arkansas_V8]

Just a guess, but if you have checked everything up top, that's about all that's left.

Maybe a fuel line gets heated and collapses.

 

[dfaulk]

it is usually when it gets hot...

I'll check that.

 

[1987 GMC Jimmy]

Stupid question, but are you 100% you have spark when it’s hot? Besides a vapor lock issue, which is a hard sell for me when you’re moving down the highway, and cracked rubber fuel lines, that’s about it. Are you still running the electric pump, or are you back to mechanical? Do you have the metal line going to the carb from the pump or has that been taken out or cut? I could see a clogged pickup, but if it’s doing this consistently on both tanks regardless of the fuel level, I would hold off on dropping the tanks.

 

[bucket]

I've been dealing with a similar issue recently, although mine is more related to how much I'm into the go pedal and how long. If I lay into the throttle, the truck goes like hell, but when it nears time to shift, it runs out of fuel and I have to let off the throttle so the pump can catch back up. Towing a heavy load aggravates the issue. The tank is clean, the lines are clear, filter is clear and the mechanical pump maintains pressure. The next step is the carb. My hunch is the float is sticking and not fully opening the needle/seat.

 

[dfaulk]

Stupid question, but are you 100% you have spark when it’s hot? Besides a vapor lock issue, which is a hard sell for me when you’re moving down the highway, and cracked rubber fuel lines, that’s about it. Are you still running the electric pump, or are you back to mechanical? Do you have the metal line going to the carb from the pump or has that been taken out or cut? I could see a clogged pickup, but if it’s doing this consistently on both tanks regardless of the fuel level, I would hold off on dropping the tanks.

I switched back to the mechanical pump and I am still using the original metal line to the carb. My mechanic put a new distributor on the truck as well. He said the same thing about it just going dead moving down the highway. It happened yesterday on the way back from work, disconnected the supply line re primed and then it cranked right up. I have driven it a week with out incident them boom. Someone suggested the sock in the tank might be clogged up.

I've been dealing with a similar issue recently, although mine is more related to how much I'm into the go pedal and how long. If I lay into the throttle, the truck goes like hell, but when it nears time to shift, it runs out of fuel and I have to let off the throttle so the pump can catch back up. Towing a heavy load aggravates the issue. The tank is clean, the lines are clear, filter is clear and the mechanical pump maintains pressure. The next step is the carb. My hunch is the float is sticking and not fully opening the needle/seat.

Yep, same here, i forgot to mention this in the original quote. Had another buddy suggested the float, but when there is no fuel going to the carb, in my case, its hard for me to believe it is the carb.

That LS swap is looking better and better....

 

[MisterB]

Might be a carb issue too.

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[gotyourgoat]

That LS swap is looking better and better....

Sadly it would only be solving the problem because you would be replacing the entire fuel system.

You mentioned fuel isn't flowing when you take the line off but when you crank it fuel comes out. That's normal, it's not a pressurized system like fuel injection.

Are you running an aftermarket filter? Have you checked the filter in the carb?

 

[omillan99]

Sadly it would only be solving the problem because you would be replacing the entire fuel system.

You mentioned fuel isn't flowing when you take the line off but when you crank it fuel comes out. That's normal, it's not a pressurized system like fuel injection.

Are you running an aftermarket filter? Have you checked the filter in the carb?

If you run one of those cheap clear filters before the carb you'll quickly be able to tell if fuel had been flowing. I would start with that and force it to stall in a safe area so you can check that. It'll at least give you an idea if its from the before or after the pump.

 

[Snoots]

Recently had a similar issue. Turned out to be the sock on the fuel pickup. It was coated with crud.

 

[gotyourgoat]

If you run one of those cheap clear filters before the carb you'll quickly be able to tell if fuel had been flowing. I would start with that and force it to stall in a safe area so you can check that. It'll at least give you an idea if its from the before or after the pump.

I can't condone that type of filter. Replaced my line from the pump to carb and got rid of over a half dozen connections. The clear plastic filter could also be seen visibly pulsing from the pump at idle. God knows what it was doing when I was playing with the loud petal. I consider my rig much less of a fire hazard without one.

 

[semperfiguy98]

Try running with the gas cap loosened a turn or so. Could be vacuum in the fuel tank as you're driving and using fuel. That fuel should be displaced by air, but if there's a blockage, then when you use enough fuel then a partial vacuum is created in the air space inside the tank, which won't allow fuel flow until the pressure equalizes. If it runs fine after loosening the cap, then you just have to find where it's blocking the vent. Good luck.

 

[omillan99]

I can't condone that type of filter. Replaced my line from the pump to carb and got rid of over a half dozen connections. The clear plastic filter could also be seen visibly pulsing from the pump at idle. God knows what it was doing when I was playing with the loud petal. I consider my rig much less of a fire hazard without one.

I run those and I've had no issue, but i was thinking just to diagnose the issue. It would be easy to go back to not having that filter.