Mechanical fuel pump after a long sit: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Jan. 8, 2012 9:05 p.m. Keith SuperDork

So, I'm trying to get the Caddy running again. It's had a good long rest. And it appears I'm not getting any fuel out of the mechanical pump. I have a glass bowl on the filter so I can see nothing's coming through.

Is there some way to prime these or ensure it's getting fuel from the tank so far away? On my old Land Rover, there's a lever on the bottom I can use to run the pump by hand. I don't see one on the Caddy 429 pump.

I'm mostly used to fuel injection and electric pumps. Who can give some suggestions?
Jan. 8, 2012 9:26 p.m. stuart in mn SuperDork

If it's been sitting a real long time, the diaphragm in the pump may have failed. To test the pump by hand you'll have to take if off the car, and try moving the arm that sticks into the timing cover.

Some old GM pumps can be disassembled, and you may be able to find a rebuild kit, but chances are the easiest thing will be to just get a new pump.
Jan. 9, 2012 7:16 a.m. 44Dwarf Dork

Easyest way to prime it is to take off the inlet hose and hook up an IV bottle http://www.motionpro.com/motorcycle/partno/08-0032 Or something like it...say soda bottle with 3/8 hole drilled in the cap and 5/16 line stuffed it to it.
Jan. 9, 2012 9:18 a.m. DavidinDurango Reader

I think Stuart hit it - I've always heard that a fuel pump diaphram will disintigrate if you let it dry out.

As mentioned, you may have some luck rigging an alternate fuel supply and praying the pump will work after a while. ???

How could anyone let such a fine automobile sit for so long?
Jan. 9, 2012 9:39 a.m. MadScientistMatt SuperDork

Agree with Stuart - probably a failed diaphragm.
Jan. 9, 2012 10:08 a.m. Keith SuperDork

So, if the pump is good and 100% functional, it should start working after enough cranking to get the oil pressure up?
Jan. 9, 2012 10:14 a.m. BoxheadTim SuperDork

Probably, if it creates a strong enough vacuum to suck gas through from the tank - I'd guess that the line is dry if it has stood for quite a while.
Jan. 9, 2012 10:26 a.m. AngryCorvair SuperDork

if you know there's fuel in the tank, you can sacrifice a gas cap to the gods of internal combustion and drill it for a standard wheel valve stem, then use that to blow a few psi into the tank. i've done it with good result.
Jan. 9, 2012 10:45 a.m. stuart in mn SuperDork

Keith wrote:

So, if the pump is good and 100% functional, it should start working after enough cranking to get the oil pressure up?

I think so. If the pump is good you shouldn't have to prime it - it will have enough power to suck the gas from the tank.

This does raise the question about the gas - are you working from a dry tank and dry lines, or is there still old gas in them? If it's a year or two old I wouldn't worry about it too much, but if the gas is older than that it should be drained and replaced with fresh gas.
Jan. 9, 2012 11:03 a.m. iceracer SuperDork

A blow gun and a rag around the filler neck will work to prime the pump.
Jan. 9, 2012 11:17 a.m. 44Dwarf Dork

pumps have a few small plastic spring loaded disks in side as check valve they'll offten gum up and unless you get a solvent (gas to them thay will not pop open or closed. If you feel safe prime it as above with rag and blow gun or soda bottle.