# Car has electric fuel pump and bypasses mechanical - ok to keep or need to fix?



## screaminggoat (Jan 19, 2021)

I've got a 400 in my 67 and it has an Edelbrock 17301 at the back near the fuel tank, feeding directly into the carb. There's a mechanical pump on the engine, but it's totally disconnected. I'm looking for advice if this is ok to run for the time being (probably a year or two, might switch to EFI once I've fixed more pressing concerns) or if I need to address it soon. The car starts well and ran fine on my drive around the neighborhood, I haven't had it out on faster roads yet since I'm still working through what needs done.

Thanks in advance for any help


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## Sick467 (Oct 29, 2019)

Shouldn't hurt a thing.


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## An0maly_76 (Dec 25, 2021)

If you are planning an EFI upgrade anyway, half the work is already done for you. And no, it will not hurt anything to leave it as is. The only thing that will happen is the mechanical's internals might wear prematurely from not having fuel flow through it, but it won't hurt the engine. However, when you upgrade to EFI, you may want to verify that the electric can handle the supply volume and pressure demands of the EFI system.


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## screaminggoat (Jan 19, 2021)

Awesome, glad to hear it! Thanks guys!


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## armyadarkness (Dec 7, 2020)

bare in mind that that electric pump is only capable of producing 7 psi, so it's not going to work for any fuel injecting.

Also, its listed as being "gravity fed", so whatever you do, dont run out of fuel.


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## screaminggoat (Jan 19, 2021)

armyadarkness said:


> Also, its listed as being "gravity fed", so whatever you do, dont run out of fuel.


How come?


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## armyadarkness (Dec 7, 2020)

screaminggoat said:


> How come?


Because "gravity feed" means exactly that... It can only push fuel out of it, not suck fuel into it, or "Draw". So if you have it mounted externally on your tank, using the existing fuel line, then it needs to be primed in order for it to work.

Or if you prefer, it wont suck gas out of the tank.

Most pumps have a "draw" rating in the spec. "Gravity" is just what it says, "it" and all of it's plumbing has to be at the lowest point of your fuel supply. Whereas a mechanical pump can prime itself and suck fuel out through the top of a fuel tank.

You may get lucky and have a siphon effect, work in your favor... but anyone here who has ever tried to prime a pump, which wasn't in order, will tell you that it's futile and can easily be impossible.

So... Dont whatever you do, don't lose prime! Or... don't run out of gas!


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## armyadarkness (Dec 7, 2020)

May sound silly, but if youve ever tried to bleed brakes or a cooling system, then you understand the importance of priming and not introducing air into a closed system.


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## screaminggoat (Jan 19, 2021)

Definitely was lucky when I replaced the fuel tank then! I’ll bear that in mind when/if I mess around back there, cheers. I do have the pump mounted below the tank, but yeah the pipe goes up and then down.


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## armyadarkness (Dec 7, 2020)

Like I said, you can certainly get lucky and have a siphon thing working out in your favor, but I wouldnt want to rely on it.

The bottom line is; yeah, while it's not going to hurt anything, you have the wrong fuel pump for your carb and car. I assume you have a reason for leaving it that way, so I won't suggest changing it... but if you ever run out of fuel and can't prime, at least now you'll know why.


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## screaminggoat (Jan 19, 2021)

armyadarkness said:


> The bottom line is; yeah, while it's not going to hurt anything, you have the wrong fuel pump for your carb and car. I assume you have a reason for leaving it that way, so I won't suggest changing it... but if you ever run out of fuel and can't prime, at least now you'll know why.


My first post in this thread was asking for advice on whether to keep it like this or change it out - I’m trying to prioritize my work and spend since I’m doing this myself on a budget. It sounds like it’s a bigger issue for usability of the car than I thought from the first couple responses, but not a safety problem. Reasonable summary?

Given that, does the quality/brand of the manual fuel pump make much difference, or am I good to get any one? Given mine has been running dry for who knows how long I think it makes sense to replace it.


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## 64Original (Jun 21, 2017)

screaminggoat said:


> My first post in this thread was asking for advice on whether to keep it like this or change it out - I’m trying to prioritize my work and spend since I’m doing this myself on a budget. It sounds like it’s a bigger issue for usability of the car than I thought from the first couple responses, but not a safety problem. Reasonable summary?
> 
> Given that, does the quality/brand of the manual fuel pump make much difference, or am I good to get any one? Given mine has been running dry for who knows how long I think it makes sense to replace it.


Why not just remove the fuel pump? It only has two bolts and is easy to get at. Block off plates are inexpensive and easy to install. Nothing personal but is should only be a 30 min to an hour job if that to complete.


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## armyadarkness (Dec 7, 2020)

64Original said:


> Why not just remove the fuel pump? It only has two bolts and is easy to get at. Block off plates are inexpensive and easy to install. Nothing personal but is should only be a 30 min to an hour job if that to complete.


The whole thing is a bit subjective.

He's asking "is it okay to run it the way he is". And the general answer that we all gave is "yes".

However, when I looked into the electric pump that he's using, it's "gravity feed", which isn't designed to draw from above the fuel level. So he could run into issues if he ever gets air bound.

Without knowing any of the other specifics on the car, I left my answer as "yes it's okay", but there are better ways to do it. That being said, if he's on a budget, then probably get a new mech pump and install it.


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## screaminggoat (Jan 19, 2021)

armyadarkness said:


> The whole thing is a bit subjective.
> 
> He's asking "is it okay to run it the way he is". And the general answer that we all gave is "yes".
> 
> ...


Yeah, exactly right - I’m trying to keep on a budget while not cutting corners. Based on what you said I’m looking at getting a mechanical pump in the next couple weeks and will put it in. The car was in pretty bad shape and it’s getting a lot better but still a lot of work left to do.


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## armyadarkness (Dec 7, 2020)

screaminggoat said:


> Yeah, exactly right - I’m trying to keep on a budget while not cutting corners. Based on what you said I’m looking at getting a mechanical pump in the next couple weeks and will put it in. The car was in pretty bad shape and it’s getting a lot better but still a lot of work left to do.


It's always best to provide as much info as possible, that way youre likely to get much more accurate responses. But based on what you mentioned, yes, I'd get a new mech pump.

That Edelbrock pump that you have now is a very generic pump and not right for your application. If your car was rough, then the PO probably was trying to bandaid something with it.

If you were going to use an electric fuel pump for a carburated vehicle, then you'd use and Edelbrock 182052, which puts out 6.5 psi and could probably suck the water out of your neighbors pool.

But theres just no reason to use a $300 electric pump, for your application


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## PontiacJim (Dec 29, 2012)

screaminggoat said:


> Definitely was lucky when I replaced the fuel tank then! I’ll bear that in mind when/if I mess around back there, cheers. I do have the pump mounted below the tank, but yeah the pipe goes up and then down.


You are good, don't over think this. I have used the parts store cheap-ass electric fuel pumps on a couple cars back in my youth. They got hooked up in the engine compartment. Never knew they were "supposed" to be used closer to the tank. I guess the electric fuel pump wasn't aware of it either or the damn thing might have stopped working. Have also used the cheap-ass electric pumps hooked to a battery on the ground, inserted the "suction" end with a long hose down into a gas tank to pump gas into an unsafe and non-approved EPA/OSHA vessel so I could put gas into another vehicle.

Did have an electric cheap-ass fuel pump, mounted in the engine bay on the fender well decide to bind up in 5 o'clock traffic 25 feet from the toll booth on the George Washington Bridge in New York City. Pulled the pump apart right in the middle of the traffic jam, freed up the stuck pump piston (maybe dirt as I had no filter), put it together, and proceeded to pay the toll and drive the 3 hours to home. Never another issue with it ever again and drove the car for another good couple years before the TH-400 went south.

The pick up tube in the tank is located near the bottom of the tank so it is under gasoline all the time. The inlet has suction and the outlet has pressure. A vacuum is created in the line from the tank and gas is drawn and begins to flow to the pump because of the sucking action of the pump. Once the gas reaches the pump it is pushed to the engine/carb. It is better to have the pump located below the top of the tank or lower than the tank as It helps prevent burnout by gravity feeding the pump and keep it as close to the tank as possible as they push better then pull.

Electric fuel pumps should use a relay so its not automatically powered when key turns - SOME Fuel pumps can pull a lot of current, so it's always a good idea to run a relay when possible, but your Edelbrock pump doesn't draw much AMPs at all.

Stock Pontiac fuel pump is rated at 40 GPM, see below. They will support up to 450HP. If you go more on HP, then more GPM flow.


*Carter Fuel Pump Applications*​
'65-'66 Pontiac Part Number -M4507 GPH-40 Pressure 5.5-7.0
'67 Pontiac Part Number M4522 GPH-40 Pressure 5.5-7.0 ​Assume your fuel line is the 5/16" size which would be stock for your year. I believe '68 went to 3/8". Here is the spec on the Edlebrock Pump *- Edelbrock part #17301 *fuel pump is a gravity fed type pump with a simple 2 wire design. It requires approximately one amp average draw at maximum delivery and works on 12 Volt negative ground systems only. It features an in-line style rotor and vane pump design. 4-7 PSI, 38 GPH for most carbureted applications and is compatible with gasoline and E85. Pump has integrated 5/16 barb fittings on fuel outlet and 5/16 fitting on included fuel filter inlet.


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## 64Original (Jun 21, 2017)

armyadarkness said:


> The whole thing is a bit subjective.
> 
> He's asking "is it okay to run it the way he is". And the general answer that we all gave is "yes".
> 
> ...


Guess I missed the part where he was going to replace the mechanical pump with a new one and get rid of the electric pump. If the electric pump was working ok then I would remove the mechanical at a cost of around $30.00 in parts but if it is not performing as it should and he is going to replace it then yes leave it like it is for a couple of weeks and then replace it.


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## Baaad65 (Aug 29, 2019)

I tried a small Edelbrock electric at the tank to feed the mechanical with no regulator and no return line, it just flooded the float bowls so I took it out immediately...bad idea I guess. So I have the original Holley 110 gph that Butler put on in 2014 with a new 5/16" braided line and never have run out of gas with a 461 about 500 hp and an 850 dp carb. And some sort of safety shut off should be used on an electric pump like an oil pressure cut out because if you're in a wreck and unconscious you can't turn the ignition off therefore the fuel pump keeps pumping...then you might be cremated on the spot, saves you from buying a casket though.


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## Jlsconstructs (Dec 3, 2021)

If the pump is running and you run out of fuel you would run the risk of burning up the pump. Pumps don’t like to run with out something to pump. I’d run it until you change over to EFI then I would reevaluate the whole system and change everything out accordingly. I agree that suction and needing to bleed the fuel line could also be a problem if you run it out of gas.


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## An0maly_76 (Dec 25, 2021)

Jlsconstructs said:


> If the pump is running and you run out of fuel you would run the risk of burning up the pump. Pumps don’t like to run with out something to pump. I’d run it until you change over to EFI then I would reevaluate the whole system and change everything out accordingly. I agree that suction and needing to bleed the fuel line could also be a problem if you run it out of gas.


OP, on the off chance the existing electric cannot deliver sufficient pressure for EFI, when you upgrade, there's a good chance that a fuel tank for an 84-87 turbo Buick would work nicely. It is a trunk-mount, strap-in, bumper-fill like your OEM, and is designed for an in-tank pump to facilitate fuel injection. There is also a rather nice pump upgrade from Walbro for higher-volume needs.


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