Electric Fuel Pump to Prime carb after car sits for period of time

Remember if you expect to run a quiet in-tank pump, pick one that fits thru the existing hole for the sender, or maybe the tank vent (smaller). As for the riveted tank vent, I drilled out the rivets, found the tank holes already euro-threaded, so it was simple to replace the stock vent with Hall's economical anti-roll-over valve assembly (now mandatory for passenger cars & light trucks world wide).

DeTomaso supplied roll-over valves on the '80-up wide-body cars and probably on Longchamps etc made after '80. But factory parts today are unbelievably expensive and mostly unobtainium. I've never, in many million miles, rolled a car or truck. But if the worst happens, I don't want to be bathing in 91-octane along with a smoking-hot engine, for want of a $50 part.

Hi Folks, was out of town for a number of weeks so electric pump installation was delayed. I have installed high near the fuel line coming out of the top of the fuel tank leading into mechanical pump. The pump is rated max PSI of 4.5. I have not yet secured the pump to the firewall to ensure it’s operating correctly….. doesn’t seem so? I’ve checked the wiring and confirm it has 12v leading to the pump and pump is making noise and can feel it’s operating when when toggle switch is activated. In my mind doesn’t seem to be pulling/pushing fuel to carb when turned on. It is a flow through pump not sure if high enough psi to get fuel to carb. Questions: is max 4.5 psi high enough to get fuel to carb for boost and is mounting correct position on fuel line out of tank to mechanical pump? Or, should it be installed on output side of mechanical pump leading to carb?

Thanks for your thoughts, Ron

Check for any small possible fuel  line joint air leaks between the pump and the fuel tank. As the fuel tank is lower any trace leak will defeat the ability of the pump to work effectively by destroying its suction.

4.5 psi is PLENTY of capacity. Electric pumps like to be mounted as LOW as possible to use the syphon effect to help the fuel flow out of the tank. They are not great at raising fuel on the intake side of the pump. With the pump down low in the car, once it has fuel to the pump, it will keep the syphon as long as fuel is available in the lines and tank. You may have to blow air into the filler neck to start a flow of fuel to the pump on initial installation.

First things first. Verify that you have the lines correctly installed, i.e., input and output and not reversed.

Also, the original hard tube fuel line that is welded into the tank itself, has a nasty habit of holing through right at the fuel level line you mostly keep.

In other words if you normally store the car with 1/2 a tank, that will be the area of the tube that is most likely to hole through AND THEY WILL.

Once you have a hole there, you have lost the siphoning ability below the hole.

I had this issue where the car would run out of fuel at 1/2 a tank level. It's a Pantera unique issue so it was a brain stumper for any of my friends to envision.

Thanks Percy and DWR46, Thanks for the input. As you know the fuel line to the Mechanical fuel pump comes out of the top of fuel tank. The current position of electric pump is close to the top of the firewall a bit below the fuel line coming out of the tank. I just checked the line connections and all are tight and no apparent leaks. I've seen some pics of the electric pump mounted high from other forum members and was easiest spot for me. I did start the engine about 5 days ago after letting it set for days but only started after my usual cold start procedure of cranking the engine for 20-30 seconds then couple pumps on the gas pedal.  The electric fuel pump did not help with cold start. I tried again yesterday and also did nothing to help with starting. I know choke is set correctly as the engine starts immediately if it sets for only 1-3 days. The pump s/b primed as I've run the engine with it connected. Just doesnt seem to be getting the suction to pull/push to the carb... Maybe a bad pump?

Hi Pantera Doug, Thanks for your input. I have the pump installed correctly; input from the fuel tank line, output headed to mechanical pump. I've run the fuel tank to below 1/4 level and never a problem with engine running. I'm still perplexed on how the electric pump pulls fuel from tank line then pushes through the mechanical pump up to carb...? Max 4.5 PSI doesn't seem enough to do that when actual output is probably only couple pound. I have not put a fuel pressure gauge on the system to test.. Thanks again, Ron

@ronwitt posted:

Hi Pantera Doug, Thanks for your input. I have the pump installed correctly; input from the fuel tank line, output headed to mechanical pump. I've run the fuel tank to below 1/4 level and never a problem with engine running. I'm still perplexed on how the electric pump pulls fuel from tank line then pushes through the mechanical pump up to carb...? Max 4.5 PSI doesn't seem enough to do that when actual output is probably only couple pound. I have not put a fuel pressure gauge on the system to test.. Thanks again, Ron

The porous fuel tube isn't that simple to diagnose. It might have been ok last week but today...

I've been through this. It isn't denial, it's just so ridiculous of a situation it becomes invisible but the symptoms persist.

Best of luck in solving but looking under the wrong rocks won't fix it.

Fill the tank completely...to the brim. If that solves the issue, it's the tube. If it persists, it's something else.

The internal pick up tube is steel. It rusts out.

Hi Doug, I also should have mentioned I replaced the fuel sending unit with fuel pickup about 2 years ago. I guess it's a possibility that the fuel pickup has failed? The one I took out had failed on the electrical side for sending to fuel gauge. I kept the old unit and just checked...fuel pickup looked good after maybe 48 years...

Thanks, Ron

There are two version of the fuel gauge sender unit. The original one has no pickup, it's just a sender. With that one the banjo on top of the tank is connected to a steel tube that goes to within an 1/8" or so of the bottom of the tank in an indented well.

That is the tube that rusts out and is not replaceable.

There is a second type, which is currently serviced that has the pickup as part of the fuel gauge sender/float assembly. It's unlikely that a recent one will rust out so fast.

I had a dead sender assembly so I replaced the float assembly with one currently serviced by Wilkinson. That tube is steel and as I remember was just yellow cad plated.

That float also had to be "adjusted" quite a bit to have the gauge read anywhere near accurately, but that's a different story.

IF you have gone to the pickup integral to the float/sender unit, scientifically you need to eliminate a tube failure as a possibility, pull it out, and vacuum/pressure test it on the bench.

In the attached illustration, the tank on the left has the original design showing #1 as the fuel banjo. Below that, not shown in the diagram is the steel pickup tube.

The second fuel pickup illustration in the center of the diagram is the replacement sender/pickup with the integral pick up.

Doug, thanks again. The old sending unit that I took out had the fuel pick up so must not have been original. Of course the one I installed did have the fuel pick up. I will pull out and vacuum test. Installing the new sending unit was not an easy task, at least not for me. After removing the fuel tank top cover I ended up taking out the side window which again was not easy. After the unit was installed my fuel gauge issue was corrected. Putting back in the side window even with soapy water around the rubber seals took some time. I’m starting to think that a simple installation of an electric fuel pump booster is getting to be a headache. Thanks again, Ron

It is a real PITA thing. " I feel your pain."

For the fuel pump, mounting height isn't going to matter because the height of the fuel connection coming out of the tank calls the shot. It's already high and the pump has to lift fuel out of the tank just to get over that hump.

My EFP is mounted low actually below the bottom of the tank on the chassis cross member and it doesn't matter a hill of beans.

SOME have gone to using the tank drain plug as the fuel line attachment point. It can be problematic as well because first you have to get the plug out without destroying the tank.

The tank has a threaded insert attached to the sheetmetal of the tank and a few have torn the tank itself trying to get the plug out.

The other thing is that the plug is SO LOW that you need to use a very tight fitting 90° fitting which MAY be subject to road hazards that originally you wouldn't need to worry about.

It's also a not very common metric size. I think from memory that it is a M22-1.0? That has VERY limited alternatives to use. In fact maybe even one or two that you may have to get from someone like Pegasus Racing?

BEFORE you pull out the sender AGAIN, you could try taking a small can of gas, disconnecting the fuel line from the tank and using that as a test to see if everything works then? If it does, it points even more so to the in tank pickup. If it has the same issues, don't even bother taking the sender out again. The problem is highly likely elsewhere.

Hi Doug, yes pain for sure. Your suggestion on testing the line disconnected for the fuel tank in another gas can is a good one. Will try that first. Don't want to go the route of line feed from drain plug at the bottom of tank, although an option, but way down the list. I'll let you know how it goes. I assume you feel that 4.5 PSI is also good to get the job done as a boost prime pump? I wonder, but not sure if a 10-14 PSI boost or lower 7 PSI would cause any issues with my Motorcraft 4300D carb...and make a difference on pull. Not sure of your carb setup or if FI. What PSI are you running for EFP. Thanks for taking the time to respond to each of my questions/comments...much appreciated! Ron

@ronwitt posted:

Hi Doug, yes pain for sure. Your suggestion on testing the line disconnected for the fuel tank in another gas can is a good one. Will try that first. Don't want to go the route of line feed from drain plug at the bottom of tank, although an option, but way down the list. I'll let you know how it goes. I assume you feel that 4.5 PSI is also good to get the job done as a boost prime pump? I wonder, but not sure if a 10-14 PSI boost or lower 7 PSI would cause any issues with my Motorcraft 4300D carb...and make a difference on pull. Not sure of your carb setup or if FI. What PSI are you running for EFP. Thanks for taking the time to respond to each of my questions/comments...much appreciated! Ron

The pressure that you get out of a stock mechanical fuel pump is plenty.

On carburetored engines you need to be concerned about the needle & seat and floats to consistently be able to handle pressures higher.

The 7psi that you read about in "Hot Rod" magazines is completely wrong for a street car. You might need that at the dragstrip on cars that really "lock up" because of the g-forces pulling fuel away from the transfer slots in the carbs but other then that it is in fact a little dangerous.

The Webers that I am running are running on 3.5psi of pressure. It supplies them with sufficient volume.

As an aside, it took a long time to get some details on some of the Shelby and Ford mid '60s race cars like the Cobras and the GT40's running Webers but guess what? They didn't even run pressure regulators, just plumbed directly from the mechanical pumps which put out....ta ta da! You guessed it! 3.5 to 4.5 psi. The EFP was there to PRIME the system, since they were constantly being torn down in between races and otherwise would need to start dry.

Anyone who has problems with not enough pressure has issues elsewhere and is confused about where to look.

The electric pump you are installing is for PRIMING the system when it is dry...and MAYBE breaking vapor lock BUT if you have vapor lock, there is an issue elsewhere, like the fuel lines are getting cooked somewhere.

Use the Holley Mighty Mite from amazon we've used dozens and dozens of them. Mount it where the fuel outlet pipe comes out of the tank. Their both small & powerful.

Ron,

Leave the pump connected to the fuel tank.  Disconnect the outlet hose or tubing and extend to a bucket or container.  Power the fuel pump and see what you get in the bucket.  

John

Thanks to all for your comments/suggestions. All very good points and tips. I'll leave the 4.5 PSI pump alone for now. Will do what John suggests first as it's the easiest for me to get access and test. If there is no fuel after testing pump into a bucket, I will know it's either a bad pump or something in the tank fuel line. The electrical connection at the pump is testing at 11.87 volts. I will let you know how it goes..... Thanks again to All, Ron

Not one of us got it right? The question I answered was 'what pump do guys use or recommend' asking for 'tips' so anybody that answered that question got it right.  Answer A uses blablabla, answer B uses blablabla He asked for opinions. Not to get into an arguement over semantics but I did answer the question. How is that considered 'wrong' to you my friend.

Pantea fuel tanks are vented... the vent hose leads to a charcoal type canister on the opposite side engine bay from fuel tank, as does mine. Very good points by all. This is what I enjoy about the Pantera Forum, most have gone through the issues of repairing or installing parts / components and are very helpful with advice / tips. I Thank you All, Ron

Yea whatever. My fuel pump suggestion IS and WAS very useful.

MJ, you are wrong about the canister, it is vented back to the air cleaner so open to atmosphere, not closed system... The fuel tank is Vented! end of story...

All, I'm checking out of this sting of comments, has turned non-productive at this point. Thanks for all the good comments and input on trouble shooting. Take care, Ron

Thanks for the suggested fuel pump type to use Sharkey- most appreciated.