fuel pump wiring for carb conversion

[BGman]

In the 914-6 tech section of PP- there is a section that describes what to do to hotwire the relay board to operate the new fuel pump when the ignition is turned:

"The 914-4 relay board has the fuel pump wired to be controlled by the fuel injection computer. Removing the fuel injection system and the FI brain, disables the fuel pump. In order to get the fuel to work again, you need to jumper some wires on the relay board. An electrical diagram of the relay board is shown in Figure 1. In this configuration, the fuel pump is powered by jumpering from another 'hot section' on the relay board. In order to wire the fuel pump to turn on when the ignition is on, wire pin 85 from the rear window defogger relay to pin 85 of the fuel pump. This is the ground lead. Then wire pin 30 of the rear window defogger to pin 86 of the fuel pump relay. I used bullet connectors and a short piece of wire to plug into the sockets on the relay board. This should work well."

I tried this today using two small jumper wires. As soon as I connected the battery, the pump started. I disconnected the battery and doublechecked that I had the right relays connected correctly. Again, when I connected the battery, the pump started running. For grins, I then went over and inserted/turned the key: the jumper wires fried and smoke filled the garage. Note to myself: I am a dumbass. Anyways, after removing the jumpers- I checked everything again ...and everything is still working correctly (got lucky).

I am assuming from the directions, that the relays need to stay in their respective places. True? Or am I supposed to jumper as instructed and remove these two relays from the board?

Ideas?

[velomann]

GMan,
Scan in a handwritten diagram of what you did....I would be interested to see because I have done this, and it did not work! I am at the same point you are on a conversion, and trying to figure out how to make it go properly. You seem to be a step ahead of me, and I am in the same quandry.....besides, if you put in a diagram, maybe somebody like the electrical genius 'Bowlsby" will take a look and give us the correct path!

[Dave at Pelican Parts]

I cannot find the article you quote there--can you provide a link to it?

From a look at the schematic, the article may have meant pin #86 on the fuel pump relay. #85 gets +12V from the FI Power Supply relay as soon as the ignition goes on, and the injection will supply a ground to pin #86 to turn on the fuel pump. The relays do still need to be in place for this.

I believe that you can get the pump to run any time the ignition is on by removing the fuel pump relay, and jumpering pins 85 and 87 on the socket for its relay. But jumpers like that are not necessarily that secure...

If you are going to run new wiring for the fuel pump, and if you want it on when the ignition is on, then you can remove the fuel pump relay--but leave the FI Power Supply relay in place. Then power your pump from the right-front pin of the four-pin connector at the left-rear of the relay board.

--DD

[SteveStromberg]

Run a jumper from the coil hot side to the pump. The pump is mounted in the stock location? Steve

[Dave at Pelican Parts]

Yuck. Use the relay. I believe in giving the coil as "clean" a power source as possible, without adding high-draw components on the same circuit.

--DD

[ruddyboys]

I agree with Dave, I put the fuel pump on the coil and the car would run rough, rewired it to a relayed wire and the car ran fine, must have been drawing to much voltage away from the plugs.

[chibone_914]

Do not run a wire from the coil to the fuel pump, unless you want them both to split the voltage and run like crap. Like Dave says, you'll need a clean 12V circuit to run the fuel pump. I just use the 12V lead that originally powered the FI pump.

[Jared at Pelican Parts]

Originally posted by SteveStromberg
Run a jumper from the coil hot side to the pump. The pump is mounted in the stock location? Steve

Bad idea. It will screw up the voltage going to the ignition, tach, and the pump

You want to run an independent power lead with a relay., I would tap into a switched 12V off the fuse box, then to a relay, then to the pump.

[SteveStromberg]

Well there seems to be a lot of book smarts here and not to much real world knowledge. A jumper from the coil hot lead will work fine even those who post here some are nay sayers. I have used this on more than a few of the 18 914's that I have owned.Steve

[914GT]

Steve, it might work fine - for a while... I'd be concerned that the extra current from the fuel pump would be too much for the ignition switch (without looking at the wiring diagram I think it feeds the coil directly). Maybe it can handle it , but not knowing the current ratings for these parts you take your chances. A relay switching current directly off the battery is best and you then know you're not stressing the ignition switch.

[Jared at Pelican Parts]

Exactamundo....

[SteveStromberg]

Well how many years might that be till it fails? Is 8 years and still counting long enough? Steve

[SteveStromberg]

If you are worried about it you could put a hella relay in and use the coil hot lead to trigger the relay. But I have been using the jumper lead from the hot side to the pump for years . I have yet to replace a Ingition Electrical portion of the key switch due to the failure on the ignition ciruit, the starter ciruit will fail long before the ingition side will. Steve

[914GT]

Guess you've done a good enough life test on it then. Any idea how much your + coil voltage dropped (points closed, engine off) with the extra fuel pump load? Also, isn't the pressure too high using the stock FI pump on a carburetor, or is there a way to regulate it down?

[SteveStromberg]

You need to swap out the pump for a Carb pump.The Facet pump is self-priming to 18" fuel lift. Standard 12 V models require only 1 amp at max. delivery I have hade good luck with this but usewith the stock mounts
.



Carter-Federal-Mogul P60504 fuel pump.


You should also install a Fuel pressure Regulator

[Dave at Pelican Parts]

Originally posted by SteveStromberg
If you are worried about it you could put a hella relay in and use the coil hot lead to trigger the relay.

Exactly!

Or, you could use the circuitry that is already built into the relay board that does that exact same thing. Check out how the "power supply relay" on the relay board works--the coil "hot" lead turns it on, and it sends a fused +12V source through to that right-front pin of the four-pin connector that I mentioned above.

It's there, it's free, why not use it? I figure the "cleaner" the power you can get to the coil, the better...

--DD

[SteveStromberg]

Dave he has a problem with his relay board as his jumpers went up in smoke. Steve

[chibone_914]

We offer the correct rotary fuel pump that is factory set at 3.5 lbs pressure. You won't need to spend more money on a Petrol King pressure regulator unless you purchase the wrong pump (5 lbs)

Sending 12V to two 12V components will place twice as much electrical load on the one single circuit.

The difference is doing the job right the first time versus possibly getting stranded on the freeway because the overloaded circuit fried a fuse, wire or worse yet, the overloaded ignition switch.

When doing this conversion, just use a little common sense and a little understanding of Ohm's law.

[Scott S]

My car is has the pump wired to the coil. It was donr this way by the PO so I thought is was correct. Being that I still have the relay board, can someone tell me where to re-route this wire? Can I simply spice into an existing wire that is going to the relay board? If so, which one/color?
Thanks!
Scott S

[chibone_914]

Hello Scott,

It is the Black/Red stripe wire from the relay board to the fuel pump. It is pin number 13 on the rectangular multi-plug at the top of the relay board (multi-plug closest to the firewall) Double check the circuit with a test light. It should be a switched 12V circuit.