In previous post I noted that my clear fuel filter between the mechanical pump and the QJet was usually near empty after taking a drive. Now I have a couple of episodes of the engine dieing after setting in traffic for a few minutes. Once I get it restarted and moving it does okay.

I can replicate the problem if I let the car idle after coming home from a drive. What I notice is that the fuel pressure (gauge between the pump outlet and clear filter) slowly drops from 5.5 psi to 0 after about 3.5 minutes of idling and 30 seconds later dies (car temp climbs from 180 to about 200 before elec fan comes on).

The fuel pump only has 6K miles on it. One other time I couldn't get fuel pressure at all I discovered a loose connection between the hard line from tank and the rubber hose to the pump inlet - so was sucking air. Tightening the hose clamp solved that.

Fuel pump does not have a return line -- car is 1939 with original tank that has been cleaned. Gas cap has a vent diaphragm which I have punctured to keep pressure from building up in tank when it gets hot. So tank is vented and can't draw a vacuum.

There is one point where the hard fuel line is within 1 inch of an exhaust pipe where the pipe and fuel line go over the rear axle. They are at an angle to each other so the exposure to exhaust pipe heat is limited to a small length (maybe 3 inches). Today I wrapped some insulating foam with aluminum foil facing around this part of the gas line, but the result was the same after a test drive.

Fuel pressure is 5.5-6.0 when started cold and filter fills to about 90% full.

Do you agree this is heat related, and is there anything that would cause the pump pressure to decline to 0 if there are no leaks between the tank and pump?

John

Sounds like you are driving my truck a year ago!

First. The clear fuel filter is very deceiving. I wish they did not make them. It does not matter when I look at mine, it's always empty. Why??? I have no idea, but it runs fine.

Second. I had the exact same thing last year. Near new pump, metal lines insulated by my headers, checked EVERYTHING!! except my near new pump. It would get hot and crap out. Fuel pressure would drop to zero when sitting idling hot. Finally actually checked the pressure and saw it low when hot. Replaced the pump and not an issue since then.

Mark

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As said above the pump may be crapping out when hot.
The feed side, and pump body itself, of the mechanical pump is suceptable to under body heat ( exhaust system, hot pavement, engine heat etc).

The feed side of the pump operates at a lower than atmosphereic pressure.
When ever the acting pressure on a liquid is lower than atmospheric, the boiling point of that liquid is lowered. So the excessive heat causes the fuel to boil very easily in the fuel line and pump body. The pump cannot move the fuel with bubbles in it.
The cure (assuming the pump is good) is to reroute the feed side fuel line away from heat and isolate the pump body from engine heat (Seals It isolator pump gasket and bolt kit).
Further: Any rubber hose fuel line joints on the feed side tend to heat up and get soft and collapse from radiant heat. The rubber hose joint between the frame and fuel pump inlet is a common spot for trouble.
Installing a electric "pusher pump" at the back of the car right near the fuel tank really helps by pressurizing the feed side fuel line. This added pressure avoids fuel line boiling (vapour lock). A 72GPH 6-7 psi Carter #P4594 pump works very well. No regulator is nessessary.
If you want , you can just run the Carter electric pump and remove the engine mounted mech pump. This 72GPH free flow rated pump will move 47GPH thru a 3/8" fuel line and common paper element fuel filter at a working (flowing) @4 PSI thru a .110" holley needle seat assembly.
(I flow tested it.) When properly mounted, the pump noise is very reasonable.

Carter P4594

fuel pump heat gasket and bolts

Replaced the fuel pump and problem is solved.

Cool!!! !!!

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I`m not sure if this was mentioned but one thing to remember is you must lube the new pump. Most fuel pumps are not lubed and in the case of a small block chevy it does little to oil the pump. The spring in the pump must be lubed with break in lube, moly lube, white lube, whichever you perfer. If not the spring will get hot and fail. I usually pack the spring area with moly lube and it`s worked very well for me.