Installing an electric fuel pump as a booster pump

[John76]

19 hours ago, Mike Self said:

I want to install an electric pump simply as a booster pump--controlled by a dash switch

Mike,

I've been toying with this idea for a while. So far I have installed a check valve near the fuel sender to keep at least some fuel in the line between the tank and pump. I also routed my fuel filter between the pump and carb, and kept it in the air stream from the fan.

My last effort was to install reflective aluminum HVAC tape to the underside of the air cleaner to help keep heat from the float bowl. The above "fixes" have kept fuel in the bowl a bit longer than about a week of sitting after a hot shut-off. 

But I still have to squirt fuel into the float bowl if the car sits for several weeks. 

My next project is to follow you with a "booster" electric pump with a momentary "prime" button and/or a continuous switch if the reliable mechanical pump decides to go south at an inopportune time.

Hope this gives you some food for thought.

John

 

[M3M3]

Why bother with complications from multiple pump systems?  Install electric pump in trunk, delete mechanical pump.  Done.

 

Electric pumps can be quiet and reliable.  And they are simple to replace and readily available at practically any parts store on the road.... Unlike mechanical pumps. 

[Dick R]

Your reasoning for using just the electric pump is sound on each point you raised. 

One of the reasons I chose to continue using the mechanical pump as the primary pump was to have a tried and true, factory-installed safety feature - when the engine stops turning, the fuel pump stops pumping gas.  Of course an inertia switch can be added to shut off the electric pump in case of a crash, but not every incident that happens where you don't want fuel continuing to be pumped is the result of a crash. I guess you could turn that around and say the same thing about the engine turning, but my choice was to keep the mechanical pump as the primary and just use the electric pump as the auxiliary carb filler.  

[Mike Self]

Gentlemen (and ladies, if one responded 😁).  Thanks for all your input. 

 

It seems there are small electric pumps without an anti-backflow valve that can be installed in series with the mechanical pump.   Methinks the easiest location would be between the sender unit's pickup nipple and the beginning of the translucent fuel line that runs through the passenger compartment.  I have a small paddle switch that's momentary in one direction and on in the other (a Renault Dauphine windshield wiper switch!) so the electric pump could serve either as a primer pump or full-time backup in case of mechanical pump failure.  

 

The most difficult part of the install is pulling out seats and carpet to run the wire from pump to dashboard.  There's already an unused connector just above the turn signal relay, meant to power the electric pump on a tii; it's switched power from fuse 11 on roundies.  

 

I still want to retain the mechanical pump due to its simplicity, longevity and ease of swapping out in case of failure (I carry a spare in my on-board spares kit).  But the electric booster would be a real time saver. 

 

As it stands now I prime the Weber with a little bottle of gas and an ear syringe, squirting the gas into the float chamber vent just forward of the carb throat.  As many times as I've had to do this over the years, having an auxiliary pump would be a real time saver.  Too bad the Germans didn't think to put a hand primer on the fuel pump like my Renaults and Sprite.  

 

Thanks again for all your comments and suggestions.  

 

mike

[John76]

47 minutes ago, Mike Self said:

There's already an unused connector just above the turn signal relay, meant to power the electric pump on a tii; it's switched power from fuse 11 on roundies.  

That Green/white fused connector tap under the dash should be used for the signal to the fuel pump relay (tab #86).  The wire is too small and connected to too many other things to be used as a power source for an electric pump.

 

56 minutes ago, Mike Self said:

The most difficult part of the install is pulling out seats and carpet to run the wire from pump to dashboard. 

Do you still have/use the plastic fuel and vent lines running from the trunk to the engine bay? If so, consider using one as a conduit for a 12 AWG power wire from the #87 relay tab (in engine bay) to the electric pump + (in the trunk). No need to pull seats or carpets ... it will fish right through. Ground the pump locally.

If the electric pump can be installed in series with the mechanical pump, then you can install it in the hose between the sender and the plastic self-sealing line. 

[John76]

12 hours ago, Mike Self said:

It seems there are small electric pumps without an anti-backflow valve that can be installed in series with the mechanical pump. 

It's been a while since I first sketched out a plan for a booster pump. This is a "work in progress" so here's a different approach for a pump that can be installed in series (Rev.2).

If the electric pump without an anti-backflow valve is used, then a bypass hose may be necessary to avoid the built-in check valve and any other resistance in the mechanical pump.

Anxious for others to chime in with their solutions. I'm in the camp of those preferring the mechanical pump as primary.

 

 

[jimk]

I would call the pump a priming pump, not a booster pump.   No need to boost pressure when the mechanical pump is there.

[TobyB]

Hey, thinking agriculturally-

 

my Case trencher has a small lever that you use to do exactly this.

You pull the lever, and it mechanically moves the pump to fill the 

settling bowl and the carb bowl. 

Just open the hood, and give it a few tugs.

It looks like the latest offering from FCP Gropeon and Autohauz have a plate

ready- made for a little 'farmering up'

 

t

 

 

 

[John76]

1 hour ago, TobyB said:

Hey, thinking agriculturally-

That is pretty corny. 😁

[tech71]

On 5/7/2023 at 4:03 PM, M3M3M3 said:

Install electric pump in trunk, delete mechanical pump.  Done.

That is the most elegant install but also the most expensive unless you can scrounge a complete pump/hangar and sender for a decent price. The sender( E30) is pretty big bucks.

Been looking, need(want ) one for Franzi

Edited May 10, 2023 by tech71

[M3M3]

14 hours ago, tech71 said:

That is the most elegant install but also the most expensive unless you can scrounge a complete pump/hangar and sender for a decent price. The sender( E30) is pretty big bucks.

Been looking, need(want ) one for Franzi

nope. none of that needed.  stock 02 sender/pickup.  inexpensive low pressure fuel pump.  mount under trunk boards or inside right quarter panel area.  it is the least expensive solution.

[tech71]

16 minutes ago, M3M3M3 said:

nope. none of that needed.  stock 02 sender/pickup.  inexpensive low pressure fuel pump.  mount under trunk boards or inside right quarter panel area.  it is the least expensive solution.

Mistakenly thought you were referring to an in tank set up, my bad.

Franzi's replacement engine has an E21 2.0 head from a 320 i so have to decide on a fuel pump set up.

[TobyB]

For some reason, I read that as 'in tank' as well.

 

t

 

[tech71]

I like the "in tank" set up but as I understand it, the hangar assembly doesn't extend quite to the tank bottom on later, larger fuel tanks.

That could be remedied with a bit of fabrication but the sender will still sit a little high so there will aways be a bit more fuel in there than indicated. Not necessarily a bad thing I guess.

Thanks @AceAndrew

Edited May 10, 2023 by tech71

[M3M3]

2 hours ago, TobyB said:

For some reason, I read that as 'in tank' as well.

 

t

 

lol..."in trunk" vs "in tank".....