Fuel Pump Failure

[Zots]

I have this in-tank fuel pump: Spectra Premium SP1138 Electric Fuel Pump (low pressure for carbureted engine.)

I have gone through 2 of them...each lasting less than 1 minute. I have 10 gallons in the tank. I have power to the fuel pump...no fuses blown.

Thanks for any Ideas...

[michael everson]

Do they just stop pumping?
What happens if you hook them directly to a battery out of the car?
Are you using a pump sock?
if not maybe debris is getting into them and locking up the pump.
Mike

[Zots]

Thanks, Mike.
Yes, they stopped pumping. I removed them and connected directly to the battery and nothing.
I installed a new pump sock so there should be no debris.
I am using a toggle switch to turn on/off the pump...spliced into the fuel pump relay control wire on the back of the fuse panel.

[michael everson]

Seems unlikely that you got 2 bad pumps but who knows. Try reversing the leads and see if it frees up. Also check to make sure you have 12 volts at the positive wire right at the pump.
Mike

[Zots]

12 volts at the pump.
Reversed leads...nothing!
Maybe I will go mechanical!

[mike223]

Are you dead heading the pump?

I see the Spectra Premium SP1138 Electric Fuel Pump is made for low pressure - but I can't tell if you can dead head it (when fuel flow stops because the float bowls are full).

I've been using a regular EFI pump with a bypass regulator for years (with carb) - no problem (excess fuel returns to the tank) - but I know for a fact that you can't deadhead those pumps (which look very similar to yours) or they die very quickly.

[Zots]

That may be it... I do not use a regulator or return line. I installed the return line but have not utilized it. I never used a return with my old external Holley and Carter fuel pumps. This is my first low-pressure in-tank fuel pump.

[Avalanche325]

Are you dead heading the pump?

Nice catch. I would bet on that.

[skidd]

I have the exact same pump in my car. Been running perfectly now for almost 2 years. Deadheaded right to my carb through the standard 5/16 F5 provided hard line. Getting a nice 5psi on the pressure gauge at my carb.
I wonder if this pump hates being wired backwards? I don't even know if it really matter.. I'm 99% sure it's a standard brushed DC motor in there. It shouldn't care one bit about being wired in reverse... but.. perhaps?
I can't seem to track down any photos of which terminals I wired to where on mine.. but.. if I do track them down, I'll post here.

[skidd]

Found it!! I remember at the time doing a bunch of research into which terminal should be +/- but.. I don't remember what I had found to go this route.
113842

[Zots]

I have it wired the same way...and that red wire connecting to the brown wire marked fuel pump on the FFR wiring harness
Thanks for the reply.

[Railroad]

Does your pump hanger put the pump to the bottom of the tank? The pump needs to stay submerged.
Is the pump pickup pressed too tightly against the bottom of the tank, overworking the pump?

[NAZ]

It appears that the failure mode is “quit running” so now you have to determine why. Three main reasons come to mind are seized (pump end or motor) or motor burnt out or motor shorted. Least invasive testing will be to test the motor with an ohm meter. Direct short will show little or no resistance. Burnt windings or other wiring issues causing an open circuit will show high resistance.

Seized will show high amp draw if motor is still OK. But if it’s seized the only way to tell for sure if it’s the motor or the pump end is to disassemble the unit.

Centrifugal pumps don’t like to be dead headed and doing so can cause damage. The typical mechanical pump found on OEM applications with carbs are not fussy about being dead headed but in tank centrifugal pumps are not the same as diaphragm pumps that have been mounted on the side of carbureted engines for the better part of the 20th century.

[Railroad]

Does your fuel pump hanger, clamp the pump excessively tight?

[Zots]

No seizures...no shorting...no amps detected.

I disassembled the first pump and found excessive carbon and wear on the commutators (...on a NEW pump with less than 1 minute of use?) I cleaned them up and reassembled (without outer case, which was cut off) and it worked.

Could dead head cause that? Seams plausible as the motor bogs down and can no longer efficiently rotate (or push/pump) fuel? I can sure see how some debris could get caught between the armature and the magnet and cause failure since fuel flows through/around it on its path.

[NAZ]

Dead heading a centrifugal pump typically does not hurt the motor -- it's hard on the pump parts (impeller, cheek plates, volute, etc.). If you find that both pumps failed the same way it may be time to go to a different manufacturer pump.

[michael everson]

You say the fuel flows through the motor windings? Wow surprised to hear that.
Mike

[Zots]

You say the fuel flows through the motor windings? Wow surprised to hear that.
Mike

Yup...in the bottom...up through the motor...and out the top! Surprised me too!!!
113863

[NAZ]

Seems crazy that a brushed electric motor is submerged in gasoline and some engineer designed it that way. In a properly designed fuel tank there is not enough oxygen (yes, even when the tank is near empty) to support combustion. The high vapor pressure of gas keeps the tank filled with fuel vapors that are too rich to burn. But with home builders making changes to fuel systems, who knows what you might find. Not such a worry with external pumps.

[mike223]

Dead heading a centrifugal pump typically does not hurt the motor -- it's hard on the pump parts (impeller, cheek plates, volute, etc.). If you find that both pumps failed the same way it may be time to go to a different manufacturer pump.

I agree - but I can't swear they're centrifugal pumps.

I always had the impression that at least the high pressure EFI pumps were rotary vane pumps (positive displacement).

I could be completely wrong on that - and I haven't taken one apart (maybe tomorrow if I've got one lying around the shop).

[CDXXVII]

Turbine Fuel Pump. Pretty interesting that fuel interacts with all the electrical internals.

[https://thefactoryfiveforum.com/attachment.php?attachmentid=113871&d=1567835079

[CraigS]

Turbine Fuel Pump. Pretty interesting that fuel interacts with all the electrical internals.

[https://thefactoryfiveforum.com/attachment.php?attachmentid=113871&d=1567835079

Yep, it's weird isn't it? But they have been doing it since the 80s. AFAIK all efi cars have intank pumps. Two huge advantages;1- the pump is as close to the bottom of the fuel as it is possible to get so virtually no chance of starvation, 2- noise is greatly reduced.
BTW I have been running a mechanical pump for 12 yrs w/ no problem. But you need two things. A front cover w/ a pump mount cast in, and an eccentric on the cam. That could be the killer on an engine built expecting an electric pump.
https://www.youtube.com/watch?v=BmjB_dJj8x8

[OVCobra]

Carbon brushes in a DC motor need to seat in and create a conductive film to ensure reasonable/long life. Your comment/observation that the brushes and comm were worn but once cleaned operated again. It would appear that the initial run did not allow the formation of the film and thus the brushes wore into the comm. The fuel running through the pump both cools it and lubricates the bearings/bushings and may also lubricate the brush/comm surface and/or be important to create the film? Spectra notes that running the pump dry will damage the pump so it may be in spite of your efforts to ensure fuel can enter the pump it is not? The repeat on a second pump, as noted above, is unlikely so suspicious. May want to go back over the pickup/screen to ensure the pump can flood once installed and submerged.
Note that these are turbine pumps and are not considered a centrifugal pump...deadheading them, while not ideal, would only cause the turbine to spin without moving fuel. Deadheading a positive displacement pump (vane or gerotor) will generate pressure and load up the pump and increase motor load and current. If left too long would likely trip a fuse.
Deadheading a centrifugal or turbine pump, as noted previously, should only impact the motor. If left absolutely deadheaded for a very long time will heat the fuel inside the pump and eventually create fuel vapour.