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Fuel flow

Jack73

New Member
Joined
Sep 18, 2017
Messages
2
Got a 73. Previous owner installed an EFP under the hood. I belief it was a generic Mr. Gasket pump. I knew I was goimg to have problems with it but rest of the fuel system is sound (new lines and new tanks). It worked for awhile while I was working on other things like installing disc brakes and the such. Now the pump want stay primed, I have to diconnect the hose after the pump hold my thumb over the hose until the pump primes. Would run the dqy like that nd even the next day start up. Eventually pump started not pumping while on incline. Changed the pump out to a hollie mini but put it back in the same spot (hoping for a quick fix to hold me over) even that cut out on incline. Looking for permnent fix solutions. Would like to stay with electric with emergency shut off options, best fuel pump placement location. I am running duel tanks.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Hey Jack. Welcome to classicbroncos!
I can't say with 100% certainty of course, but at least part of your trouble is likely the location of the pump. As it sounds like you're leaning towards.

Electric pumps (especially basic ones) don't like to pull. They much prefer pushing and are much better at it. Over the last 40 years or so I have only heard of a handful (or less) of people who've had even remotely decent luck with a pump mounted in the front of the truck. The only way to really do it right is to mount it towards the tanks.
With dual tanks, the "easiest" if that's possible, would be to put it right in front of the valve under the seat. But mo betta still would be to mount the pump somewhere in-between the two tanks, then run the valve outlet hose back to the pump, then back to the engine. Short of using two pumps, one per tank, this would be the best.

The only other thing that comes to mind is what some do with two pumps. That's to use only the main tank with the electric feed pump, then another small cheap pump used to transfer fuel from the side tank to the rear tank.
Some do that when their selector valves fail, but most that are doing the transfer method are running EFI with a single high-pressure (and more expensive) pump on the frame rail back by the main tank.

But no matter what, get the pump back as far as you feel you can. It can only help the pump stay primed. If all you do is get it down to the level of the tanks, you're on the right path. But if you can get it down low AND back as far as you can, better still.

If you don't drive the truck much it would be entirely possible that the first pump was just getting weaker from the new modern gas and sitting. Only new EFI pumps seem to be able to handle that for very long. But since you changed the pump to a new one and it's acting the same, then I'd have to say it's all about location, location, location...

Good luck.
And again, welcome. Post up some pics of your rig sometime if you can too.

Paul
 

ntsqd

heratic car camper
Joined
Jan 30, 2005
Messages
3,225
Loc.
Upper SoKA
Don't let that its possible to have junk from a bad fill plugging a new pick-up sock in a new tank slip past you. I'm not leaning towards that being the problem, but keep it on the shelf should other, more likely causes prove to not be a problem.

Modern fuel doesn't need much of a lowered pressure (vacuum from fuel pump) to reach the lower end of its boiling temperature range. A moderately warm day coupled with a strong pump is enough to do it. "Vapor lock" on a day & situation that otherwise shouldn't produce it.

Not all fuel hoses are created equal and modern fuels are hard on rubber hoses. If you've got a hose that went soft on the suction side it could be collapsing under pump vacuum. That itself may not be enough to cause fuel to not flow, but if it creates enough of a restriction to reduce the pressure on the fuel allowing it to boil you will have vapor lock (see above). Be wary of kinks in the suction side hoses. Suggest that "Emissions Barrier" hose, in particular the EFI rated but perhaps all of it, may be less prone to collapsing under vacuum due to its construction. It is not inexpensive.
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
I bet you have an air leak in your fuel feed line to the pump.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
I bet you have an air leak in your fuel feed line to the pump.

Yes, you should test for a leak in the suction line. It will allow air in and break the pump's prime. Has your car got dual tanks? The selector valve would be my first suspect.

You can test for the suction line leak by putting air pressure into the gas tank with an air hose. Just a bit of pressure is needed. Any leak will show up.
 

SHX669

Bronco Guru
Joined
Jan 9, 2009
Messages
1,997
Every "rotary vane" electric pump I've installed the instructions have said " install as close to the tank as possible AND below the fuel level of the tank " .
When I bought the '76 it had two " diaphragm " style pumps ; one for each tank that were operated/ changed with the fuel gage switch on the dash . That setup seemed to work fairly well. Both those pumps were mounted close to their respective fuel tanks
 
OP
OP
J

Jack73

New Member
Joined
Sep 18, 2017
Messages
2
Hey Jack. Welcome to classicbroncos!
I can't say with 100% certainty of course, but at least part of your trouble is likely the location of the pump. As it sounds like you're leaning towards.

Electric pumps (especially basic ones) don't like to pull. They much prefer pushing and are much better at it. Over the last 40 years or so I have only heard of a handful (or less) of people who've had even remotely decent luck with a pump mounted in the front of the truck. The only way to really do it right is to mount it towards the tanks.
With dual tanks, the "easiest" if that's possible, would be to put it right in front of the valve under the seat. But mo betta still would be to mount the pump somewhere in-between the two tanks, then run the valve outlet hose back to the pump, then back to the engine. Short of using two pumps, one per tank, this would be the best.

The only other thing that comes to mind is what some do with two pumps. That's to use only the main tank with the electric feed pump, then another small cheap pump used to transfer fuel from the side tank to the rear tank.
Some do that when their selector valves fail, but most that are doing the transfer method are running EFI with a single high-pressure (and more expensive) pump on the frame rail back by the main tank.

But no matter what, get the pump back as far as you feel you can. It can only help the pump stay primed. If all you do is get it down to the level of the tanks, you're on the right path. But if you can get it down low AND back as far as you can, better still.

If you don't drive the truck much it would be entirely possible that the first pump was just getting weaker from the new modern gas and sitting. Only new EFI pumps seem to be able to handle that for very long. But since you changed the pump to a new one and it's acting the same, then I'd have to say it's all about location, location, location...

Good luck.
And again, welcome. Post up some pics of your rig sometime if you can too.

Paul
Thanks for the info. My plan is to relocate the pump near the aux tank . I had reran a combo of hard an soft lines already and should have taken the the time then to relocate the pump then but wasnt having problems with the pump at that time. Any suggestions on pumps? Oh, put a pick in the garage but dont know where else to post photos, still trying to figure his forum out.
 

KeithKinPhx

Sr. Member
Joined
Jan 8, 2017
Messages
444
For years I had mine positioned on the frame rail by the aux tank. It pulled directly from the valve tank selector under the drivers seat. Never had an issue.

Recently bit the bullet and went FiTech EFI. Put a 23 gallon main in with an in-the-tank pump. Can't seem to get my self the throw the old pump away. Bought it Pep Boys in the 90's.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Jack,
There is absolutely nothing wrong with a mechanical pump like your car came from the factory with. I actually went back to a mechanical because doing an electric pump right has too much safety equipment that needs to be wired in.
But, if you do need to run an electric pump, with dual tanks, the best way is to get rid of the manual selector valve. Then mount both the pump and electric selector valve back on the frame between the two tanks. That way the suction lines to both tanks are as short as possble.
 

metal1

Full Member
Joined
May 2, 2016
Messages
259
Loc.
hidesert ,socal
X2 on the stock mechanical pump ,they work great and it is what they came with ,but maybe there is some other reason for an electric pump and as others have posted it needs to be as close to the tanks as possible or practical ;) good luck
 

ntsqd

heratic car camper
Joined
Jan 30, 2005
Messages
3,225
Loc.
Upper SoKA
I use only a oil pressure kill switch on my various electric pump installs. Used to use the switch from a Chevy Vega, but those are hard to find these days. Now can get them from Summit. They have 3 terminals: pump, running power supply, & cranking power supply. That switch, a couple of wires, and a relay is all that it takes. No big deal to me.
 
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