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Fuel delivery in a 312

Posted By joey 2 Weeks Ago
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joey
Posted 2 Weeks Ago
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Hello gentlemen

Here is the situation: fuel pump on 56 TBird (about 25K miles since new) was working fine but leaking oil through weep hole. Ethanol, thinks I. Figured I’d replace it. Also replaced the short flex line on the input side. New fuel pump (Carter 73063) worked fine for about 10 mi. Then fuel pressure fell to zero on pressure gauge on fuel rail. Engine would idle but would not carry any kind of load. Figured pump was faulty, replaced it with another. Experienced identical results—started up fine, showed steady 5 lb pressure, drove perfectly for about 10 mi, then began to run rough and ultimately died on side of road, presumably of fuel starvation. Pressure gauge at zero again. Barely idled. Limped home.

Retreived original fuel pump from trash bin and saw it was an Airtex 4406. Compared Carter and Airtex side by side, noticed Airtex had a slightly shorter pump arm travel. Significant? Maybe. Bought a new Airtex 4406 and installed it. Also replaced new flex line (tiny i.d. about 1/8” on brass fittings) with flex line with larger diameter fittings. Excellent steady fuel pressure initially, but after 7-8 miles of driving (engine up to temp) fuel presssure at idle drops to zero but recovers to 3 lb or so upon rpm increase. So i disconnected line to fuel tank and drew gas from a jerry can—gauge still read zero, although i only ran it that way about 30 sec. I blew compressed air backward into hard fuel line and heard gas in tank bubbling immediately. Tried replacing gas cap with a new one, then put the old one back then tried no cap at all. No difference. Fuel line filter element was clean, replaced it anyway.

My understanding is that fuel line assy from tank was replaced about 25000 miles ago. Car is always garaged, never sees weather, so I doubt the hard fuel line is rusted. I haven’t had it up on a lift yet, but am assuming there must be a rubber section of fuel line somewhere after the tank. Could that be the trouble? Tank is original to the best of my knowledge.

But its odd to me that there was never a problem until old pump was pulled off.

I will replace the line from the tank forward if i have to....Never done one on a bird but I’ve done shorter lines and brake lines.

Anyway, any suggestions or advice? Thank you.
DryLakesRacer
Posted 3 Weeks Ago
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Not sure if this helps but I run 1oz of Marine fuel stabilizer with every tank hoping it will slow down/stop any ethanol damage. So far in 8 years and 10k miles good.
I would open the fuel pump and see what’s failed. A high percentage of the diaphragms are the same and you may be able to get one that will be ethanol friendly and not fail by a tear. Good luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.
joey
Posted 3 Weeks Ago
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Thanks DryLakesRacer. Yes, I opened the first one up and it looked perfect. The others I sent back for refund.
DryLakesRacer
Posted 3 Weeks Ago
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Try Www.classicpreservation.com The guy advertises fuel pump kits for ethanol. You can always give them a call. Just another shot...

56 Vic, B'Ville 200 MPH Club Member, So Cal.
paul2748
Posted 2 Weeks Ago
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Any chance there may be some gunk in the tank?  Sometimes something in the tank will get sucked into the outlet and clog it up.  Once the pressure is off, it falls away until the pump starts to suck again.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Dobie
Posted 2 Weeks Ago
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I had that happen on a '53 I had. It would sometimes run out of gas with a full tank; drove me bat shit crazy. After replacing everything in the fuel system except the carb and tank I pulled the the fuel sender and had a look inside with a bore scope. I found the culprit was a seal from a bottle of additive a previous owner must have dropped in accidentally. It would make it's way to the tank outlet and stop fuel flow. I managed to get it out with a shop vac and never had another problem. 
miker
Posted 2 Weeks Ago
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FWIW. My 55 has an access plate in the trunk to allow removing the fuel gauge sender and you can look in the tank. Exercise caution, it's full of fumes. My bird had a handful of raffle tickets in it. 1/4 tank or less they cut the fuel off. No telling what you might find. I also replaced the hard line from the tank forward. We had to cut and splice it in front of the rear wheel on the outside of the frame. If there's a way to replace it with the body on the frame I never figured it out. That was on a hoist with nothing in the way.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ
joey
Posted 3 Weeks Ago
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Thank you gentlemen. I guess my next step will be to access the tank and check forgunk.

Couple questions.
Is some fluctuation of pressure in the fuel line outlet normal? Mine varies between 1 - 5 psi depending on rpm.

Is it normal to retain pressure after shutdown, even for a couple hours? And if engine is hot at shutdown for pressure to rise slightly, maybe 1 - 2 psi for awhile?

Do any of these symptoms point to some kind of flow obstruction?
joey
Posted 3 Weeks Ago
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Is some fluctuation in the fuel rail normal? Mine varies depending upon load.

Is it.normal to retain pressure after shutdown for a few hours? And if engine is hot at shutdown, for pressure to rise slightly, like 1 - 2 lb?

do any of these symptoms point to some kind of flow obstruction?


Ted
Posted 3 Weeks Ago
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At a steady state rpm, the fuel pressure is expected to be constant.  Under a load versus idle conditions, the fuel pressure will be less simply due to the engine taking in more fuel.
 
It’s not unusual for the line from the fuel pump to the carb to remain under pressure for extended periods of time after stopping the engine.  I would be concerned if it did not stay under pressure for awhile after shutting off the engine as that would be an indicator of a poor needle seat in the carburetor or weak check valve at the fuel pump.

Lorena, Texas (South of Waco)




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