Definitive way to wire an electric fuel pump for a Pre EFI Bullnose

[Tarheel Blue]

I’ve spent the last 4-5 days/ nights reading every possible method and thought on the subject. I ultimately pulled the trigger on purchasing the Carter A68301 oil pressure switch, a Hella 5 pole relay and pulled an inertia switch from a ‘95 F150 at the local yard.

I’m very confident in these selections, so if we can, I’d like to not get into the whole “better options” discussions.

Where I’m looking for advice from the people I I trust, is in the “definitive” way to run the wires.

Let’s start with what I’m attaching to;

‘85 F150 4.9L converted to duraspark many years ago.

I’ve installed a 33 gal Bronco tank in the rear and have a Bosch 6700 FDM that will supply fuel to either my existing YFA or, in the near future, a Sniper TBI unit.

I’m good on the fluid side of things but would like to hear opinions on the electric side. And if you do respond with your suggested way of wiring, PLEASE tell me WHY you like your way AND what it is about the other suggestions that you don’t like.

I’ve kinda zeroed in on this schematic and will probably be following it to the T. However there are a number of variations that could be made.

First is where to place the inertia switch. Some folks want it before the relay and others say to place it after. Even Ford changed their mind at some point around ‘91-‘92 and this is probably my biggest hang up. The inertia switch that I pulled from a ‘95 has what I’m guessing are 14ga wires coming from it. While everything I read about the wires to the pump suggest 12-10ga wires. Seams like a problem to me. However the EVTM for an ‘85 shows the switch just before the pump.

The other area that has me conflicted is the suggestions of the inertia switch affecting ground as opposed to power. I’m clueless on this one.

Another place I’ve read something about having the inertia switch control the 87a tab on the relay. I completely don’t understand what they’re trying to do there.

There are probably a couple of other ideas out there, but you get why I’m asking for advice.

Thanks in advance and Cheers!

[RenoHuskerDu]

We sidestepped all that thought process because our Bullies are diesel. Less fire risk. We just wire the pump to the ignition On position.

I admire your thoroughness. We have one gasser Bully but it's a stock block pump.

[Gary Lewis]

For reference I've included the schematic from the '85 EVTM, below. And I would wire it exactly the way it shows, which is essentially the way you've diagramed, with one exception - your priming switch. Your diagram indicates you plan to use a toggle switch, and I would NOT do that. Instead I'd use a push button. A toggle could be accidentally switched on to bypass the inertia switch in an accident, which could be a major problem. A push button switch probably wouldn't.

Also, tell me more about the FDM. Is this an EFI FDM from the later trucks? If so I need to tell you about the issue I had when doing the same thing - way too much fuel pressure. I put a return-style regulator in the engine compartment and fired it up, only to find the pressure gauge oscillating, and spiking too high. I had to put a dead-head style regulator after the other one to get steady fuel pressure at the proper level.

You can read about it, and see my video, here.

[Tarheel Blue]

For reference I've included the schematic from the '85 EVTM, below. And I would wire it exactly the way it shows, which is essentially the way you've diagramed, with one exception - your priming switch. Your diagram indicates you plan to use a toggle switch, and I would NOT do that. Instead I'd use a push button. A toggle could be accidentally switched on to bypass the inertia switch in an accident, which could be a major problem. A push button switch probably wouldn't.

Also, tell me more about the FDM. Is this an EFI FDM from the later trucks? If so I need to tell you about the issue I had when doing the same thing - way too much fuel pressure. I put a return-style regulator in the engine compartment and fired it up, only to find the pressure gauge oscillating, and spiking too high. I had to put a dead-head style regulator after the other one to get steady fuel pressure at the proper level.

You can read about it, and see my video, here.

I completely agree that the switch should be momentary, just not sure if I’ll need it or not. In theory, the three pole oil pressure switch should provide a prime function, but we’ll see how it works.

The Bosch 6700 FDM is a stock replacement for the Bronco tank. It is running through a Holley 12-880 by-pass regulator that can be adjusted as low as 2 psi, so the 4-6 psi for the YFA should be no problem. I have been cautioned to be alert for possible pulsations but there are modulators that easily handle that if needed.

 

[Gary Lewis]

I completely agree that the switch should be momentary, just not sure if I’ll need it or not. In theory, the three pole oil pressure switch should provide a prime function, but we’ll see how it works.

The Bosch 6700 FDM is a stock replacement for the Bronco tank. It is running through a Holley 12-880 by-pass regulator that can be adjusted as low as 2 psi, so the 4-6 psi for the YFA should be no problem. I have been cautioned to be alert for possible pulsations but there are modulators that easily handle that if needed.

I don't see how the oil pressure switch can provide a prime function. With no pressure P & S will be connected and the light will be on. With pressure P & I will be connected and the pump will run.

I think you might like the push button for priming.

As for the regulator, that's the one I am using and I had the pulsing problems. I didn't know about modulators, but the 2nd regulator was on hand, so I used it.

[FuzzFace2]

I don't see how the oil pressure switch can provide a prime function. With no pressure P & S will be connected and the light will be on. With pressure P & I will be connected and the pump will run.

I think you might like the push button for priming.

As for the regulator, that's the one I am using and I had the pulsing problems. I didn't know about modulators, but the 2nd regulator was on hand, so I used it.

As for priming what dose it on our year EFI trucks?

I thought it was getting a signal from the computer when the key was turned on and that cant happen with you (yet?).

Why not pick up the power when cranking at the solenoid / relay on the fender?

It would be getting power as soon and you started turning the motor over where the PSI switch would not send power to it till the oil PSI came up to close the switch.

Now I said yet? do we know how the after market EFI system deals with this?

Dose it's computer do this like the factory one does?

Have you looked into how that system gets wired and maybe you can use most of it with a jumper or 2 to work with the carb till then? Then pull the jumpers and wire it like the EFI system wants?

Sorry if I am throwing a wrench into the gears

Dave ----

[Gary Lewis]

As for priming what dose it on our year EFI trucks?

I thought it was getting a signal from the computer when the key was turned on and that cant happen with you (yet?).

Why not pick up the power when cranking at the solenoid / relay on the fender?

It would be getting power as soon and you started turning the motor over where the PSI switch would not send power to it till the oil PSI came up to close the switch.

Now I said yet? do we know how the after market EFI system deals with this?

Dose it's computer do this like the factory one does?

Have you looked into how that system gets wired and maybe you can use most of it with a jumper or 2 to work with the carb till then? Then pull the jumpers and wire it like the EFI system wants?

Sorry if I am throwing a wrench into the gears

Dave ----

Only the EFI trucks prime. The rest of us just crank until we have gas as the e-pump gets full power in Start.

[Tarheel Blue]

Only the EFI trucks prime. The rest of us just crank until we have gas as the e-pump gets full power in Start.

You have both hit on one of the biggest hurdles that I’m trying to understand (there will be more questions later about other areas), and again, I’ve been reading for days and can’t seem to figure out the best way to go about getting a short ( 3-4 second) prime activity prior the the starter actually engaging. I want the bowl of the YFA full of fuel prior to the engagement of the starter.

In my thinking, the simple action of turning the key to run, pausing a second or two and then turning the key further to start. If I’ve wired it correctly, there would be power to the pump in run ( Duh!, the pump has to have power any time the key is at RUN ) and of course in start.

What am I missing?

[Gary Lewis]

You have both hit on one of the biggest hurdles that I’m trying to understand (there will be more questions later about other areas), and again, I’ve been reading for days and can’t seem to figure out the best way to go about getting a short ( 3-4 second) prime activity prior the the starter actually engaging. I want the bowl of the YFA full of fuel prior to the engagement of the starter.

In my thinking, the simple action of turning the key to run, pausing a second or two and then turning the key further to start. If I’ve wired it correctly, there would be power to the pump in run ( Duh!, the pump has to have power any time the key is at RUN ) and of course in start.

What am I missing?

The oil pressure switch will only close the contacts when the engine is running. So just turning the key to Run won't prime the carb.

And you do NOT want to bypass that permanently. When I got Big Blue the sump was FULL of gas because someone bypassed it and the PO left the key in Run. I drained 6 quarts of oil and 7 quarts of gas out.

If you want to prime it put a pushbutton switch in to temporally bypass the oil pressure switch. Turn the key to Run, push the button, let up, and crank.

[Pete Whitstone]

You have both hit on one of the biggest hurdles that I’m trying to understand (there will be more questions later about other areas), and again, I’ve been reading for days and can’t seem to figure out the best way to go about getting a short ( 3-4 second) prime activity prior the the starter actually engaging. I want the bowl of the YFA full of fuel prior to the engagement of the starter.

In my thinking, the simple action of turning the key to run, pausing a second or two and then turning the key further to start. If I’ve wired it correctly, there would be power to the pump in run ( Duh!, the pump has to have power any time the key is at RUN ) and of course in start.

What am I missing?

I think most EFI systems have some type of check valve that holds pressure in the system in between engine runs, so priming is not really a concern. I don't really have part numbers to refer to or anything, but I think that's supposed to be how it works. Most of my experience with EFI is with foreign stuff though, maybe the domestic manufacturers don't do that.