34 fuel pump problem

Pretty open ended question? Without knowing what exactly your problems are and what procedures you've attempted to "fix" them . . . and what conclusions you've come too - can't really add much of value here. ;)
 
I changed fuel line, installed new, and rebuilt mechanical pumps. I added electric 6volt pumps, changed to 12 volt Holly blue pump. After about 20 miles I have 0 fuel pressure. Checked fuel pick up in tank,added a screen to the end of pick up, cleaned tank. Have been a gear head all my life, lived on and operated a farm, and never had any thing puzzle me like this. Can't figure this one out.
 
If the pump is working something is blocking the fuel. In a safe location for fuel vapors start with the line into the electric fuel pump. Can you blow air back into the tank (use low pressure of just a few psi here). If that line is free, connect it back up to the pump and disconnect the outlet and see if you get fuel through the pump. Is there a filter in the line? Check for fuel before and after the filter. Can you blow air through the line from the electric fuel pump to the mech fuel pump? If so, connect it back up and see if you get fuel to the mech fuel pump. So on and so on. Something is blocking the fuel somewhere along the way, need to locate where the blockage is.

I have seen lots of issues with rust continually plugging up a filter and/or messing up a pump. A fuel pump will move the fuel if it has free access to it! Another thought is any air leaks into the fuel line ahead of the pump so that it is sucking air? The Holly pump can be taken apart to see if there is anything internal to the pump (contamination) causing the problem. Ethanol in the fuel can play havoc with the whole fuel system.
 
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Have screen on end of pickup, fuel free flows from tank when line is disconnected tried non ethanol gas with no luck. I have tried every thing me and all my buddies can think of. Out of options!
 
Then try a different pump. I can guarantee you a good Holly pump with move clean fuel through a clean line with no air leaks. Works all day every day all over the place. One of these items is not functioning for it not to work.

Contaminated fuel
Clogged fuel line
Clogged fuel filter
Air leak in fuel line
Fuel pump is not working

What often happens is you get frustrated on an issue like this and keep overlooking a simple problem. The only way to sort this out is to totally forget about anything thing you have tried before and start at the beginning and check things out. I realized you believe you have checked everything, but you haven't, because this is a very simple system and it is still not working for you. Start again at step one and work it one step at a time until you locate the problem. There is no magic answer, it takes a step by step approach that does not assume anything is OK because you already checked it!

Here's an idea for you. Get several feet of rubber hose of the correct size. Make a fitting for the tank outlet and the fuel pump inlet and outlet. Now connect up the hose all the way from the tank to the engine compartment. See it that will move fuel. That should eliminate a lot of areas and narrow the problem down.
 
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Take the pump loose from the stand with the flex hose still attached to gas line. Put the pump arm against anything that will hold and push the pump up and down to simulate pumping action of the push rod. If gas does not flow then you know you have a problem other than the engine. If you are using a known good pump, then you know the problem is between the pump and tank.
 
You say after 20 miles you have 0 fuel pressure. How do you know that? Are you using an under hood liquid filled fuel pressure gauge? If you are, don't trust that gauge. They liquid filled fuel pressure gauges get warm and when they do the indicated pressure drops to 0. Seen this a few times, they are much better if you drill an itty bitty hole in the bottom to dump the liquid. This usually gets rid of the "warm so no pressure reading" .

Just mentioning this incase your gauge is telling fibs.

I've been through a car with "0 fuel pressure when hot and engine quits" he'd been fitting this for ages, in his testing he'd fitted the liquid filled fuel pressure gauge, this lead him to chase the "fuel" problem. Well the gauge was telling him it was a fuel pressure problem. It was a bad coil! Job actually took 10 minutes, did it while talking to him. It was an easy one, he popped the hood, I lent in, saw the pressure gauge, put my hand on the coil, nearly burnt my hand, it was that hot. Change coil, good to rock n roll.

If not, how are you diagnosing no fuel pressure? What are your symptoms?
Martin.
 
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