Power source for an electric fuel pump...

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ecksrash
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Power source for an electric fuel pump...

Post by ecksrash » Fri Sep 16, 2016 10:57 am

I have a '66 squareback that I'll be converting to fuel injection. Where would be an acceptable place to source the power for the pump? The pump I'll be using is a Walbro GSL392 and it requires a 20amp fuse. Where would be the best place to install the fuse? Thanks for your insight...

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Marc
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Re: Power source for an electric fuel pump...

Post by Marc » Fri Sep 16, 2016 11:47 am

You should have a safety circuit to turn off the pump should the engine stall. A Hobbs switch that only closes when the oil pressure is above a certain setpoint is the most common way of doing this on racecars, but I know of none that can be set low enough to keep the pump running at hot-idle on an ACVW.
Another way is to use a relay that's controlled by the Term 61 (charging system warning light) voltage. You'll need to also rig a temporary-on (like a horn button or spring-return toggle) within reach so you can override the safety feature to bring up pressure for startup; there are fancier ways to do this but this is simple and also allows you to drive in the event of generator failure:
http://www.speedyjim.net/schem/pump.gif
Note that this setup gets its source power via the ignition switch (Term 15). Considering how rare & expensive that switch is for an early Type III, I wouldn't do that. The relay must be energized for the pump to receive power, and that can't happen unless the engine's running and the generator's putting out, so there's really no reason to not just tap off unswitched Term 30 power upstream of the ignition switch.
I've seen some variations in early Type III wiring layouts (between US-and non-US-market cars) but I believe they're all the same so far as the Term 30 wiring...a 6mm wire to the lighting switch, and two 4mm wires from there to the fusepanel and to the ignition switch feed. The one to the fusepanel should only be carrying current for a few minor loads (horn, radio, domelight) so it shouldn't have any problem in carrying another ~10A - I'd be inclined to tap off of it where it goes to the fusepanel for an inline fuse going to Term 30 of the fuel pump relay.
http://www.vintagebus.com/wiring/t3-66-euro.jpg

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Marc
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Re: Power source for an electric fuel pump...

Post by Marc » Fri Sep 16, 2016 1:38 pm

Some folks prefer to use a fuelpump relay from an FI Rabbit/Golf instead - they sense that the engine's running via a connection to Term 1 on the coil, and also run the pump for a second or two when you first turn on the key. Works well, but I've seen too many of those relays fail to trust them (carry a spare or a jumper wire with male spade ends).
http://www.glenn-ring.com/temp/fuel_pump_relay.jpg

Note that problems have been reported when using these with an MSD ignition.

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Re: Power source for an electric fuel pump...

Post by ecksrash » Fri Sep 16, 2016 4:23 pm

Thanks Marc...

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Piledriver
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Re: Power source for an electric fuel pump...

Post by Piledriver » Mon Sep 19, 2016 1:21 pm

Given the current draw of that monster, it will need its own 12 ga line from the battery at least.
(I do this on my square for the AC fans, the 044 pump and gas heater)

Any modern ECU will have a fuel pump relay control line, use that to control the fuel pump via a near load relay and fuse. The CIS relay works on carb'd cars well, as long as it stays dry---early golfs had issues with that.

Another method is to run a large bus wire up to a second fuse box to run everything that draws serious power like headlights etc via relays... Makes a huge difference in lighting power, and keeps the large loads off the ign switch and old fuse box/wiring. The original wirting (headlights etc) can be used to control the relays.

I'm looking at that for the coming weekend, replacing multiple 12ga feeds with a single 6-8 ga feed.
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Re: Power source for an electric fuel pump...

Post by Marc » Mon Sep 19, 2016 2:38 pm

You didn't mention what F.I. system you'll be employing and I was thinking in terms of D-Jet. What will your operating pressure be? That determines the running current draw. Up to about 40 psi a 15A fuse and 14GA wire (if under ~15') would be sufficient (which shouldn't overtax the stock 6.0mm B+ wire or the 4.0mm wire to the fusepanel) but if it needs to be higher than that by all means give it a dedicated supply wire and fuse of higher capacity. Starting surge shouldn't be high enough to warrant a fuse rating greater than ~twice the normal running current. Fuse it near the source (not the most convenient place but it'll protect the wire in the event of a short).
http://autoperformanceengineering.com/html/fpspecs.html

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Piledriver
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Re: Power source for an electric fuel pump...

Post by Piledriver » Tue Sep 20, 2016 2:40 am

`66 model ~Equivalent to an 044 Bosch.... Not Djet i'd bet.
At least it isn't the huge E85 twin screw pump Chip runs. (Slightly smaller version of the Veyron pumps)

I run a 25A fuse on my 044, it draws 13A dead headed at ~180PSI. Fuse still gets warm when running at ~8A continuous.
(One of the things I'm looking to move out of the stock fusebox RSN)
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Chip Birks
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Re: Power source for an electric fuel pump...

Post by Chip Birks » Tue Sep 20, 2016 8:16 am

Piledriver wrote:`66 model ~Equivalent to an 044 Bosch.... Not Djet i'd bet.
At least it isn't the huge E85 twin screw pump Chip runs. (Slightly smaller version of the Veyron pumps)

I run a 25A fuse on my 044, it draws 13A dead headed at ~180PSI. Fuse still gets warm when running at ~8A continuous.
(One of the things I'm looking to move out of the stock fusebox RSN)
He's just running the standard inline Walbro 255. Nothing special. Make sure it's nice and rubber mounted/isolated from anything metal. Mine drove me crazy. It was louder than my unmuffled turbo exhaust. My new pump mounted in tank is whisper quiet. I'll never go inline again.

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