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Electric Fuel Pump Questions

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Red20 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Red20 Quote  Post ReplyReply Direct Link To This Post Topic: Electric Fuel Pump Questions
    Posted: Aug/24/2017 at 2:28am
It really seems like there are issues external to the mechanical fuel pump itself assuming it's in good working order. But if you do use an electric pump, why not just block off the mechanical pump altogether and run the electric pump. If you're concerned about failure, carry a cheap spare to get you home.

In any case, I run a 3 pole oil pressure switch. Power out terminal (P) connects to fuel pump or fuel pump relay (preferred), normally open (I) terminal connects to ignition switch ignition circuit, normally closed (S) terminal connects to the starter solenoid for power when cranking. When power is applied during cranking, the power goes through the closed switch to the fuel pump. When running, the oil pressure closes the normally open switch sending power from the ignition switch to the fuel pump. If the engine dies for any reason or oil pressure gets dangerously low, the fuel pump will shut off. An inertia switch inline to the fuel pump relay or pump itself could be an additional fail safe.
1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bobsterfl Quote  Post ReplyReply Direct Link To This Post Posted: Aug/22/2017 at 3:59pm
My car sits for extended periods of time and it always took a lot of cranking to get it started.  When I first built the engine, I sourced an electric oil pump from Mallory to pre-lube the engine.  I have also now added a Carter electric fuel pump spliced into the fuel line at the tank.  I mounted the pump outside of the passenger compartment in case of any leaks. It's mounted to the floor pan where it kicks up behind the rear seat. It's a little noisy, but I only need it to prime the fuel system or for engaging in authorized speed contests. LOL.  Carter is a good brand, been around as long as I can remember and is trouble free.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/16/2017 at 7:58pm

Thanks for the tip, Keith. Just yesterday I put some pieces of rubber hose over parts of the metal fuel line that run close to the engine, but too early to know if it helped or not.  I'll check out "Cool Tube".

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Jul/16/2017 at 7:42pm
IMO I would start insulating the lines before installing another pump. I have a feeling that's not going to cure your problem if you really do have vapor lock in the lines. Try insulating the lines where it's closest to heat sources like the exhaust and the line that runs from the pump to the carb since it's close to the block and heads. If you notice an improvement, keep going and you'll probably fix it. I've used "Cool Tube" from Boom Mat on several cars with very good results.
In order for that pump to overcome vapor lock, the pressure will have to a lot higher than you needle valve and float can handle.
As for a return, believe it or not, you'll add more heat to the fuel than cool it which will make the problem worse. That's one of the reason the OEM's did away with it on FI systems.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote rons Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 6:29pm
I have a '78 Concord "6". So, there are many more lines under the hood. The line from the tank to the charcoal canister in your car is a vapor line. The fuel tank vapors are purged from a vacuum port on the carb base. I wonder if you could run a second 1/4" fuel line back to the tank. I did that in my Hudson. The fuel is returned in a circulating path cooling it off and eliminating " bubbles" in the fuel line. That required me to make a hole in the fuel filler pipe, and add a .030 restrictor fitting in line, to maintain fuel pressure. I also wrapped the lines in mylar  ( obtained at Jegs).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 4:49pm

Duane, thanks for your diagram. It explains why you have the check valve.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 4:47pm
Originally posted by rons rons wrote:

First, why is your car vapor locking? I live in Tucson, so we have similar temps. Does the '72 have a feedback system. That is, is there a 1/4 fuel line going back to the tank from the gas filter. The fuel filter will have two outlets ... 5/16" to the carb  & 1/4" to the gas tank. This is there to prohibit vapor lock/starvation. The later nipple must be in the top position. Have you checked the fuel pump outlet pressure? When Fpumps get weak from age they lose efficiency... hence fuel starvation, especially under load. I believe that the Professional 10700 is a pump that is designed to  replace the mechanical pump entirely(AKA geroter pump) . I would advise after verifying that the system is up to par, then add an Airtex 8012. It is a full flow style, meaning that fuel will have very little , if any, resistance, passing from the tank to the mech pump. Solenoid style( like this one) are made to be installed in line. They can be turned off whenever you wish to run on the mech pump alone.  They are good for priming when the car sits for more than week or so. There are some issues running any electric pump full time through the mech pump. Collision is one. Oil pressure two pole switches are made for that. When oil pressure drops to below 15psi the current is halted to the EPump.  2nd. running gas pushed by an Epump through the mech pump depends on the mech pumps diaphrams not leaking, but if they do fuel can enter the crankcase. Keep this in mind. Best of luck. Ron

There is a second line going back to the tank, but I believe that this is just a vent line.  It goes to a small rollover valve on the driver's side above the tank.  In the engine bay it connects to the vacuum canister, not the fuel filter or pump.

I changed the fuel pump when the problem first started. The new mechanical pump is a NAPA B-0107-P.  I also just picked up an electric pump from Napa, but I haven't installed it yet. 

Good thought on the diaphragm. If I have to run a wire to the oil pressure switch anyway I  might as well just run it to a toggle under the dash instead and turn on the electric pump only when I need it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rockAMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 4:30pm
There is also the consideration that the electric fuel pump must be mounted above the bottom of the gas tank and the outlet side (pointed towards the front of the car) mounted at a 45 degree angle upward. That places a heavy limitation on the size and style of electric pump to use. I bought the Airtex pump - it is cheap and easily available - but it was too big to meet the mounting requirements. I never run the electric pump while the engine is running.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rockAMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 4:06pm
The pump I use is self-priming. Not sure about Airtex which is a much bigger physical size. Below is a diagram of what I did. It has worked well for me. I would not install an electric pump inline with the mechanical pump. The mechanical pump will have trouble drawing fuel through the electric pump if the electric pump is switched off.


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Post Options Post Options   Thanks (1) Thanks(1)   Quote rons Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 3:59pm
First, why is your car vapor locking? I live in Tucson, so we have similar temps. Does the '72 have a feedback system. That is, is there a 1/4 fuel line going back to the tank from the gas filter. The fuel filter will have two outlets ... 5/16" to the carb  & 1/4" to the gas tank. This is there to prohibit vapor lock/starvation. The later nipple must be in the top position. Have you checked the fuel pump outlet pressure? When Fpumps get weak from age they lose efficiency... hence fuel starvation, especially under load. I believe that the Professional 10700 is a pump that is designed to  replace the mechanical pump entirely(AKA geroter pump) . I would advise after verifying that the system is up to par, then add an Airtex 8012. It is a full flow style, meaning that fuel will have very little , if any, resistance, passing from the tank to the mech pump. Solenoid style( like this one) are made to be installed in line. They can be turned off whenever you wish to run on the mech pump alone.  They are good for priming when the car sits for more than week or so. There are some issues running any electric pump full time through the mech pump. Collision is one. Oil pressure two pole switches are made for that. When oil pressure drops to below 15psi the current is halted to the EPump.  2nd. running gas pushed by an Epump through the mech pump depends on the mech pumps diaphrams not leaking, but if they do fuel can enter the crankcase. Keep this in mind. Best of luck. Ron

Edited by rons - Jul/15/2017 at 4:07pm
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