Can't believe fuel pump simply quit - -

[CCCC]

while merely sitting. 68 Suburban w 327 started/ran great a few weeks ago. Today - no start - no fuel to carb. Pump has no more than 200 miles on it, but 3 years old. Plenty of gas in tank, fuel lines from tank to pump and pump to carb are clear (air test), and the pump PULLS 12" of vac and holds it static. But, no push on the output side.

Have never been inside one of these mech pumps. What beside the diaphragm is in there to go wrong? Can't believe it would pull/hold 12" vac if the diaphragm were leaky. Maybe a check valve setup in there? If such a valve were malfunctioning, seems like the pump could pull vac yet push nothing. No?

I have an identical new pump here to install - would rather not use same type pump if it is likely to go bad while just sitting (am suspecting ethanol as a factor). Would you go with an electrical pump back by the tank? If so, what make/type?

Thanks for any insights.

[LSUMurse]

I had an electrical pump when I tried going with a Holley TBI. I can't say I really liked it. I didn't think the noise would bother me, but it did. It's not extremely loud (especially with the sound deadening jacket), but I could still hear it. Just annoyed me.

Maybe try a different brand mechanical pump?

[alsriv2]

I would suspect the ethanol to be the culprit as well. After you get it running again, take that old pump apart to isolate the damage and report it back to us.
Also, it is possible the fuel screen in the tank has become clogged with the growth of crud that happens in the ethanol fuel systems. You might have to take a look inside the tank at the float/screen fuel inlet.

[CCCC]

Had a used electric pump sitting here - tried it on the fuel feed line - does not pump the fuel. Now, am thinkng maybe that electric pump is not any good either. Then too, elect pumps push a lot better than pull, so maybe the line is too long and air is getting in and defeating the vac.

Or is there something back at the tank restricting fuel flow? When I run 20psi air in from the front end of fuel line I can hear air bubbling up through fuel in the tank. But - upon suction, might something be shutting off the flow at the tank end? Has anyone experienced such?

Like to have a spare elect pump along for energencies - maybe I'll buy a new one to test the line from tank with a known good pump.

[hammer]

replace your hoses, air is getting in there, rubber hoses do go bad.

[CCCC]

OK - my disbelief was justified - it was NOT a pump problem. After a temp electric pump wouldn't work either, I started at the tank and worked forward checking for air leaks, All rubber hose sections are new - so not that - but found that two of the three connector joints (steel line to hose) would not quite tighten.

Took them apart - the PO went fancy and used compression fittings on the steel line - not well done and not good. They had worked loose and were letting air into the line. Fixed those spots and the pump now goes full bore - happy 327.

Those comp fittings do not look like a good idea for fuel line. I always have used a double flare type fitting where needed - and otherwise simply slip the fuel hose over the steel line and use a clamp - many. many trouble free miles that way.

Anyone else agree on the comp fittings? Don't most guys use the hose over steel line, with clamp, method?

[cdowns]

i'd check the filter inside of the quadrajet carb to see if it is clogged with crap

[Fitz]

Originally Posted by CCCC

while merely sitting. 68 Suburban w 327 started/ran great a few weeks ago. Today - no start - no fuel to carb. Pump has no more than 200 miles on it, but 3 years old. Plenty of gas in tank, fuel lines from tank to pump and pump to carb are clear (air test), and the pump PULLS 12" of vac and holds it static. But, no push on the output side.

Have never been inside one of these mech pumps. What beside the diaphragm is in there to go wrong? Can't believe it would pull/hold 12" vac if the diaphragm were leaky. Maybe a check valve setup in there? If such a valve were malfunctioning, seems like the pump could pull vac yet push nothing. No?

I have an identical new pump here to install - would rather not use same type pump if it is likely to go bad while just sitting (am suspecting ethanol as a factor). Would you go with an electrical pump back by the tank? If so, what make/type?

Thanks for any insights.

Looks like you've solved it. I do agree with you, compression fittings are not a good idea for gas lines. Double flares or AN fittings are the way to go. I relocated my tank to the back of the truck so it just made sense to install an electric pump back there.