fuel issue

[454dually]

i have an 84 c30 454.... runs great until it reaches running temp. 180 degrees or so, then dies like it's out of gas. i can fill the bowl with gas through the vent and it runs fines fine until it's gone. let it cool down and runs fine again. any ideas? thx

[zieg85]

Weak fuel pump would be my first thought.  Not a lot of money or hassle to replace if you don't know the history of it.

[bd]

Do you hear hissing if you loosen the fuel tank cap once the symptoms occur?  How many lines connect to the fuel pump?  Check fuel pump vacuum (draw), output pressure and delivery volume.  Inspect the condition of all of the rubber fuel hoses at the tank and fuel pump.  Verify that none of the fuel lines are in close proximity to the exhaust or other source of high heat.  Replace the fuel filter(s).

[454dually]

Weak fuel pump would be my first thought.  Not a lot of money or hassle to replace if you don't know the history of it.

new fuel pump was installed when i bought the truck.

[454dually]

Do you hear hissing if you loosen the fuel tank cap once the symptoms occur?  How many lines connect to the fuel pump?  Check fuel pump vacuum (draw), output pressure and delivery volume.  Inspect the condition of all of the rubber fuel hoses at the tank and fuel pump.  Verify that none of the fuel lines are in close proximity to the exhaust or other source of high heat.  Replace the fuel filter(s).

new fuel pump, new filter, new tank, new sending unit, new cap. the only fuel line in proximity to heat is the steel line from the pump to the carburetor which runs close to the block. i know the big blocks run on the warm side and i considered that steel line might be vapor locking... there are 3 lines on the pump, input from tank selector valve, overflow back to tank selector valve and output to carb. vacuum draw and pressure check fine when cold, haven't been able to check while hot as it only happens on the road.

[bd]

Have you verified that none of the rubber lines are kinked or perforated?  Loosen the tank fill cap the next time symptoms occur to make sure the tank is properly vented through the vapor canister and not developing a vacuum.  With the fuel cap removed, try blowing <20 PSI of regulated air through the 1/4" return line leading back to the tank from the pump to verify the line isn't kinked or otherwise restricted - the return line exists to cool the fuel pump and limit vapor lock through a constant flow of fuel.  Have you checked fuel pump volume?  It should pump ~1 qt in 20 seconds of cranking.  What were the draw and pressure measurements?  Recheck the inlet filter in the carburetor to make sure it hasn't restricted and isn't installed backwards.

[454dually]

Have you verified that none of the rubber lines are kinked or perforated?  Loosen the tank fill cap the next time symptoms occur to make sure the tank is properly vented through the vapor canister and not developing a vacuum.  With the fuel cap removed, try blowing <20 PSI of regulated air through the 1/4" return line leading back to the tank from the pump to verify the line isn't kinked or otherwise restricted - the return line exists to cool the fuel pump and limit vapor lock through a constant flow of fuel.  Have you checked fuel pump volume?  It should pump ~1 qt in 20 seconds of cranking.  What were the draw and pressure measurements?  Recheck the inlet filter in the carburetor to make sure it hasn't restricted and isn't installed backwards.

Thanks for your help. Sounds like a very good place to start. I will post after I make the suggested checks.