73-87 Chevy _ GMC Trucks > Crew Cabs

Starving for fuel


Hey guys, my 78 dually w/454 is driving me a little nuts right now running out of fuel, kind of. It will run great for 30-45 min going down the road and then just starts running out of gas. Same on both tanks. I switched the Qjet out real quick the the Eddy, no difference. Have changed the mechanical fuel pump twice. No difference. Put an in line pressure guage before the carb., reads perfect at start up but when fuel issue starts goes down to 2-3 pounds and then 0. I pull the supply line from the pump at this point, turn truck over and get nothing from pump. It's not vapor lock. I have pinched the return line from pump to tank to no avail. Had to have it towed home last time.. very frustrating because the next morning you go out and it starts right up!? Maybe rubber line from tank to frame rail line collapsing? Any thoughts would be appreciated.

What is the fuel pressure at cold startup? 

While cold, remove the fuel inlet hose (supply line coming from the tank) from the fuel pump and connect a vacuum gauge in its place to measure fuel pump draw while cranking/running the engine - should measure >20" Hg.  Reconnect the supply line and disconnect the outlet line to the carburetor.  Route the outlet line into a suitable, >1-quart container.  Unplug the B+ lead from the distributor to defeat ignition.  Have a fire extinguisher handy and ready for use along with a few shop rags to soak up any spilled liquid fuel.  While an assistant cranks the engine, monitor the flow of fuel.  It should pump 1 quart in 20-30 seconds.  This establishes a fuel delivery baseline. 

When the symptoms recur, measure the fuel pump draw again.  If there is a significant decrease in fuel pump vacuum the pump and pushrod are suspect.  Little to no decrease in vacuum indicates the problem is rearward of the pump.  You may have rust/debris/etc accumulation in the fuel tank or the supply line maybe perforated/cracked/collapsing.

I agree, check for kinked rubber hose in your preliminary checks.

Thanks for the replies. Fuel pressure at start up is 8-9 psi. I'll check flow and hoses this weekend. Leaning towards I may have to drop the tanks. After 39 years they may have some junk built up in there (sarcasm). Just seems odd both at the same time. May need fuel pump #3. Will post findings. Thanks again for taking time to reply.

So it took me a while to get back to this, but maybe the solution will help someone. It was pretty simple. The rubber fuel line from the tank diverter valve to the frame rail solid line was collapsing with the suction from the stock mechanical pump. Calif. fuel additives finally got to it. Purchased some high pressure, and pretty expensive fuel injection hose and replaced. Been fine ever since. About 2 months now.


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