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)

[Bulldog9]

So I've been researching how this applies to the 912E, and have come up with a couple options. Someone on the 912E board suggested to wire it directly with an oil pump cut off switch, and I found this website

http://www.how-to-build-hotrods.com/electric-fuel-pump.html

It seems like a good way to do this. Has anyone tried this? Makes sense to me, especially as it retains the pump while crank ability. Here is a schematic for the oil pressure switch.



The 912E has a double relay for the fuel pump. One side is connected to a wire harness that runs to the vehicle, the other half ran to the brain. I've managed to do most of my modifications leaving most of the stock wiring and such in tact, so I'd like to keep doing that and just jump the other side of the relay through an oil pressure switch. I'm thinking to find the pin that grounds the relay in the run position (like the jumper in this thread) run it through the OP switch and call it done. This would keep the run while starting function and the on while running with oil pressure feature, and in the case of a stall, key left on, etc. Fuel pump will not run.

But some good news, I put 5 gallons of fuel in the tank tonight and pumped about 2 quarts into a glass jar, with no filter to clean out any debris or crap in the lines and it came out clean as a whistle. After letting it sit for a few days will do it again to see if fuel in the lind=es loosened up any crud. I even poured it through a paper filter back into the gas can and there was little to no debris in the paper. Looks like I got a great tank!