HOW TO: run the fuel pump for carb conversions, the easy solution! Options

[SirAndy]

Back by popular demand, Sir Andy's "HOW TO" series presents:

HOW TO: Run the fuel pump for carb conversions

There are numerous tech. articles out there that cover this issue.
When you switch from the stock FI to carburetors, you have to install a low pressure carb fuel-pump.
But, since the FI fuel pump is controlled by the FI brain, removing the brain means the wires to the fuel pump won't give you 12V ...

There are a lot of "band-aid" solutions out there, some people remove the pump relay and add a jumper there, others even run the pump off the coil!
While all those solutions work (more or less) they all lack one thing, you're now running the pump without a relay! (and in case of the coil, without fuse as well)

The best (and also easiest!) solution is to trick the relayboard into believing that the FI-Brain is still connected ...

And it's as simple as connecting one wire from the 4-prong FI connector to ground.
You keep the stock fuel pump relay and fuse and you use the stock wires to power the new fuel pump.
Below you'll see 2 pictures showing how to attach the wire. on the pump side, simple make 2 more extension wires with "male" connectors on one end and plug them into the stock (roundish) plug for the stock fuel pump.
No need to hack into the original harness!!!

This install is clean and simple! (and cheap!)

In the pics below the thick red wired replaces the FI-Brain ...
(IMG:style_emoticons/default/smash.gif) Andy

(IMG:http://www.914world.com/bbs2/uploads/post-11-1109378319.jpg)

(IMG:http://www.914world.com/bbs2/uploads/post-11-1109378417.jpg)

[Jonathan Livesay]

HOW TO: Run the fuel pump for carb conversions

I tried this on my '74 with carbs which had been running the fuel pump off the coil. No luck, checked the black/red wire at pin 13 for continuity to the original fuel pump plug and that was good , double checked that my ground on the 4 tab connector was good, but still nothing. I traced the black/red wire from pin 12 which used to go to the aux. air regulator in the FI harness but was now cut off near the distributor, and had continuity all the way back to the fuel pump plug. Get everything but volts when I turn on the key. Fuel pump turns on with key when I plug it into the other tab on the 4 tab connector. Any ideas what I am missing here? Or what else I can try? Any guidance would be greatly appreciated. (IMG:style_emoticons/default/idea.gif)

[SirAndy]

I tried this on my '74 with carbs which had been running the fuel pump off the coil. No luck, checked the black/red wire at pin 13 for continuity to the original fuel pump plug and that was good , double checked that my ground on the 4 tab connector was good, but still nothing. I traced the black/red wire from pin 12 which used to go to the aux. air regulator in the FI harness but was now cut off near the distributor, and had continuity all the way back to the fuel pump plug. Get everything but volts when I turn on the key. Fuel pump turns on with key when I plug it into the other tab on the 4 tab connector. Any ideas what I am missing here? Or what else I can try? Any guidance would be greatly appreciated. (IMG:style_emoticons/default/idea.gif)

Are all the relays in place and working properly?
(IMG:style_emoticons/default/idea.gif)

[Jonathan Livesay]

I tried this on my '74 with carbs which had been running the fuel pump off the coil. No luck, checked the black/red wire at pin 13 for continuity to the original fuel pump plug and that was good , double checked that my ground on the 4 tab connector was good, but still nothing. I traced the black/red wire from pin 12 which used to go to the aux. air regulator in the FI harness but was now cut off near the distributor, and had continuity all the way back to the fuel pump plug. Get everything but volts when I turn on the key. Fuel pump turns on with key when I plug it into the other tab on the 4 tab connector. Any ideas what I am missing here? Or what else I can try? Any guidance would be greatly appreciated. (IMG:style_emoticons/default/idea.gif)

Are all the relays in place and working properly?
(IMG:style_emoticons/default/idea.gif)

Yes sir. I even put all 4 relays and both fuses in and tried the relays in every conceivable variation in case one was bad. I realize that some of the relays don't do anything, but just in case I misunderstood which were the power and fuel pump relays. The 12 volts to the tab on the 4 tab connector comes through the power relay doesn't it?

[SirAndy]

Yes sir. I even put all 4 relays and both fuses in and tried the relays in every conceivable variation in case one was bad. I realize that some of the relays don't do anything, but just in case I misunderstood which were the power and fuel pump relays. The 12 volts to the tab on the 4 tab connector comes through the power relay doesn't it?

The *ground* wire on the 4-tab connector grounds the relay so it can provide 12V to the fuel pump.
Normally, that ground switching is done by the FI brain.

In hindsight, i probably should not have used a red wire for ground.
(IMG:style_emoticons/default/rolleyes.gif)

[Jonathan Livesay]

Yes sir. I even put all 4 relays and both fuses in and tried the relays in every conceivable variation in case one was bad. I realize that some of the relays don't do anything, but just in case I misunderstood which were the power and fuel pump relays. The 12 volts to the tab on the 4 tab connector comes through the power relay doesn't it?

The *ground* wire on the 4-tab connector grounds the relay so it can provide 12V to the fuel pump.
Normally, that ground switching is done by the FI brain.

In hindsight, i probably should not have used a red wire for ground.
(IMG:style_emoticons/default/rolleyes.gif)

Oops sorry the other tab, the "last ditch" nonfused power for fuel pump tab (the one opposite the ground tab. The one that Elliot Cannon pictured in post 11 on this thread. I am just wondering if the fact that that one runs the pump means that the power relay is OK. Could my relay board have an issue?

[SirAndy]

Oops sorry the other tab, the "last ditch" nonfused power for fuel pump tab (the one opposite the ground tab. The one that Elliot Cannon pictured in post 11 on this thread. I am just wondering if the fact that that one runs the pump means that the power relay is OK. Could my relay board have an issue?

Yes, yes and yes.

That one comes off the power relay and should have 12V .
And yes, the relay board can certainly be kaputt, the solder connections can come lose. Have you checked the underside?


The whole reason i did this writeup was to show people that you can use all the existing wiring and relays to run your carb fuel-pump without any hacks.

And yes, i consider pumping 12V from a different relay into the fuel pump feed wire a "hack".
(IMG:style_emoticons/default/shades.gif)

[Jonathan Livesay]

Oops sorry the other tab, the "last ditch" nonfused power for fuel pump tab (the one opposite the ground tab. The one that Elliot Cannon pictured in post 11 on this thread. I am just wondering if the fact that that one runs the pump means that the power relay is OK. Could my relay board have an issue?

Yes, yes and yes.

That one comes off the power relay and should have 12V .
And yes, the relay board can certainly be kaputt, the solder connections can come lose. Have you checked the underside?


The whole reason i did this writeup was to show people that you can use all the existing wiring and relays to run your carb fuel-pump without any hacks.

And yes, i consider pumping 12V from a different relay into the fuel pump feed wire a "hack".
(IMG:style_emoticons/default/shades.gif)

So if all else fails I could run off the 12V side of the 4 tab connector through an in line fuse under the relay board cover to the fuel pump and no one but me (and you I guess) would ever know. Would that still be a hack? (IMG:style_emoticons/default/smile.gif)