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Old 06-19-2009, 11:44 PM
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Boiling fuel

Boiling fuel does not mean you have an air leak. Boiling fuel will occur if you exceed the boiling point.

The boiling point will increase as pressure increases. What is your fuel pressure at idle?

The fuel will also boil if your block/pump is to warm. Was your engine/pump cold to the touch while fuel was "boiling"?

I have experienced fuel boiling with the new gasolines. A winter blend will boil very easy. In my case I took steps to reduce engine and underhood temps.

If fuel arrives to the pump under positive pressure then air can not leak into the fuel line. Some things that prevent positive pressure at the pump inlet:
1. Gas tank not vented.
2. Fuel line restricted or too small.
3. High pressure drop filter upstream of pump.
4. Fuel tank sock plugged.
5. Climbing a steep grade.
6. Fuel tank lower elevation than fuel pump.
7. Carb calling for more fuel than system can deliver.

If your system does not provide positive pressure to the pump suction then your pump may cavitate in severe cases then form bubbles and low flow. Your car should have positive pressure to the pump during idle, if your fuel level is higher than your pump and your tank is vented. Is your fuel level higher than the pump?

Your fuel was boiling at idle with a cold to the touch fuel pump?
In idle the fuel pump is not moving fuel most of the time; instead the pump is dead headed. If your fuel pump is cold to the touch and the fuel is "boiling" I would think it would be caused from the energy the pump is putting into the dead headed fuel; thus not the root cause of your engine stall.

That being said, you did not mention the possibility of a leaky diaphragm.
When you assembled the fuel pump was the pump spring in the correct tension state while installing the diaphragm? Was the diaphragm new or old stock?

Last edited by 001mustang; 06-20-2009 at 12:45 AM.
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