stock 348 dies after running for ~1/2 hour

59K9

59K9

Well Known Member
Supporting Member 3
sounds live vapor lock to me...check to see if any exhaust components shifted near the steel line......I've been fighting demons on my '60 impala...I've done everything I can think of hoping I could locate the issue without pulling the tank...I installed a fuel pressure gauge in the cabin to see what my acceleration pressure is...doesn't look good as my idle pressure is 3 psi...tossed my c02 extinguisher just in case an issue develops...I'll bet the WOT doesn't have more that 3 psi and is running so lean is bucks and snorts over 3000 rpm...
 
Lt.FrankDrebin

Lt.FrankDrebin

Well Known Member
Thanks guys. I think looking into the short stretches of rubber hoses seems to be the next logical step. I don't believe I've ever replaced them since I've owned the car. I had the fuel tank out about 15 years ago and I cleaned it out. The sender is NOS and was installed around that time.
 
blkblk63ss

blkblk63ss

Well Seasoned Member
Supporting Member 5
Lt.FrankDrebin said:
Thanks guys. I think looking into the short stretches of rubber hoses seems to be the next logical step. I don't believe I've ever replaced them since I've owned the car. I had the fuel tank out about 15 years ago and I cleaned it out. The sender is NOS and was installed around that time.
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If the hoses are possibly cracked and sucking air and if the gas cap is not vented that can amplify the lack of the fuel supply issue. Have you tested the cap for one way operation of it??? You can suck on the inside of fuel side ,but unable to blow out to outside of cap .
 
DIV1RACER-2

DIV1RACER-2

Well Known Member
Supporting Member 12
Back in the days gone by i had this problem w/ several customer vehicles .. The best diagnostic procedure i found was disconnect the fuel line at the tank and connect a vacuum gauge to the line . If my memory is correct start the car on the gas in carb and there should be about 17-18 inches of vacuum at the tank .. It will be less if it is a hose or connection leaking , plug one end of fuel line and pull a vacuum on the line .. it should hold a vacuum ... If not the fuel line has a leak somewhere !!
 
skipxt4

skipxt4

Well Seasoned Member
Supporting Member 18
When I had the 350 engine in my 64, one day, it would only start, if I primed the carb.:dunno After playing around for a few hours, I found out, both Fuel Pump mounting bolts, were loose.:doh Not loose enough, for the pump to fall off, but 1/2 turn loose. After I tightened them, and primed the engine, it fired up, and ran perfect.:good Never had that problem before. I'm assuming vibration caused this.
 
62_Conv_2-4s

62_Conv_2-4s

Well Known Member
Possible the excentric on the camshaft has worn down letting the new fuel pump work but when play developers in the fuel pump after it breaks in the worn excentric on the camshaft may not move the fuel pump lever enough to keep fuel flowing.
 
Lt.FrankDrebin

Lt.FrankDrebin

Well Known Member
I think I determined the culprit to be the fuel pump. Engine died again today like clockwork and this time I pulled the inlet hose off the fuel pump and connected a hose that I had going into a gas can next to the car. It wouldn't start back up, so that means it's the fuel pump, right? There was fuel in the line. This pump is only about 6 months old. Can anyone recommend a reliable fuel pump? This one is a Herko brand.
 
Jeffrey Osstyn

Jeffrey Osstyn

Well Known Member
Supporting Member 3
Lt.FrankDrebin said:
I think I determined the culprit to be the fuel pump. Engine died again today like clockwork and this time I pulled the inlet hose off the fuel pump and connected a hose that I had going into a gas can next to the car. It wouldn't start back up, so that means it's the fuel pump, right? There was fuel in the line. This pump is only about 6 months old. Can anyone recommend a reliable fuel pump? This one is a Herko brand.
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Not so fast. The correct way to test a pump is to measure the amount of fuel by volume pumped during a set time frame. Fuel pumps usually don't stop working after 1/2 hour running, then reset and work again after a certain shut down time.
So, run the engine until it quits, use your pump inlet hose in bucket and disconnect the inlet to the carb, put this in an empty container. Now crank the engine for say 15 seconds, may have to do it a couple times. Measure the output vs time.

I bet it is not the pump. If you think about how they work. Diaphragm and two check valves.
If you do buy a new pump, try to find one that can be disassembled, not crimped together.

So, disassembly and inspection is possible.
 
Jeffrey Osstyn

Jeffrey Osstyn

Well Known Member
Supporting Member 3
If the fuel is blocked at the outlet of the pump, vapor lock or other, the pump can't pull up more as it has nowhere to go. Disconnect the line at the carburetor. Try it.
 
catdoctor

catdoctor

Well Known Member
On my 348 which had the glass fuel filter when I was breaking in the cam running some rpm’s the glass bowl was almost full of fuel at the start but after 20-30 minutes of running the bowl filled up with bubbles and very low with fuel and ran real rough due to going into vapor lock . Solved this with a return line.
 
Lt.FrankDrebin

Lt.FrankDrebin

Well Known Member
Not sure how vapor lock works, but one of the times the engine died, I disconnected the line between the pump and a carb. No fuel was being pumped. The last time the engine died, no fuel was being pulled. There was fuel in the long line from the tank because I was able to suck some out with little effort.
 
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