Persistant fuel starvation at 1/2 tank.

[TStark]

Hi,

It appears i can't use more than 4 gal without getting bucking and fuel starvation occuring.

Upon procuring the car the fall, starvation would occure at any lank level under prolonged load.
replaced the fuel filter element in the engine bay with some improvement in visible flow.
Fuel flow was still compromised after 5 minues, so replaced the factory electric with a Facet electric 2.5-4 psi, that seemed to make a major difference in visible flow at the carb inlet, flowing into a container.
After removal of the old pump, took it apart to fine some fine rusty sediment on the internel screen. aha i said.

Facet has a pre-filter. Used hard lines and minimal hose on suction side of pump. Also found the gazinta and gazouta on backwards, now its pulling on the larger diameter tank outlet verses the smaller diameter return.

Still, Everything is great till i get to 1/2 tank. No audible vacuum upon removing cap.

Removed sender unit, inspected sock screen and found it clean and no debri.
Inspected and pressure tested dip tube for cracks - nothing.

Searches here revealed a return line orifice, that i appeared to be missing.
I simulated one by flaring a section of hard line, then maching it down so it restricted return flow.

Still, fuel starvation after 4 gal used, just above 1/2 tank. I can only go about 115 miles.

Before replacing Facet pump, what you say?

'75 1800 32ADFA

[RoyBatty]

is it possible that the pickup line inside the tank has a hole at the 1/2 full location?

[TStark]

Suspected that also.
When i inspected the tube was without flaw. Except the wires to the gauge were failing, so i replaced it with a good spare that i also checked for any holes, and the symptom persists with the different pickup.

Oh, and i sticked the tank, the indicator was accurate, there was four inches of fuel remaining.

[carl]

It sounds like the pickup tube is not extending down far enough into the tank.

[DanD]

Are you getting a vacuum in the tank ? loosening the cap would solve that. Is you pump mounted high ? Pumps can sometimes be good at pumping out, but lousy at drawing from the source. Mounting the pump lower than the tank can create a siphon effect, where the fuel draws itself to the pump.

Also check all your fuel lines, and make sure there is no air leaking into the line.

[TStark]

As been said, no vacuum present, and dip tube inspected, then and replaced.

Yes, pump is mounted as low in the trunk as it can possibly be

However, I was mistaken, new pump is not Facet, it Mr Gasket 42S 2.5-4 psi. 42 GPH. I've seen other documents saying it 28 GPH. Flow at the carb is still meh.

Next i'm checking for a crushed hard line between tank and engine.

[TStark]

Tried to remove hose from pump outlet, to check flow there. It wasn't that great.

However the brass outlet popped off the pump housing. Press fit into plastic, ugh.

Pump had some check valve in its outlet, found it quite restrictive to blowing through it. Popped that out.

Flow improved, but the fitting now seeped gas after pressing it back in.

So diagnosis will resume after procuring and installing a better pump, again.

[seabeelt]

Why the electric pump? How about the good ole mechanical one on the side of the engine block?
R/

[TStark]

Thoughtful question, i'll consider that

Though '75, It was factory with electric, the rubber standoffs, original pump, wires, relay, inertia switch, etc.

[jagonza]

i have the same issue, did you ever get an answer - i have changed filters, looked at wiring, checked make up air, hoses, dip tubes , tank, etc nothing worked yet, any help would be helpful, i am down to the fuel pump i guess

[blazingspider]

Have you checked the integrity of the rubber fuel line hoses that dive underneath the car once they exit the trunk? I've heard stories about old hoses that look OK but begin sucking air into the fuel line because they have become porous over the years.

[kmoses]

I was had the same problem when I was using Facet pump 40-104, car ran great untill fuel level showed 1/2 tank or less. Switched to Facet pump 40-148 and the problem seems to happen now only when there is a few gallons in the tank. The last time the fuel starvation happened was this weekend and when I filled up, it took over 9 gallons to fill the tank.