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

[Gary Lewis]

It would be lots better than trying to keep it running. I think it is a good idea.

[Les Kerf]

I added an inline electric fuel pump to my 74 F-350 farm truck (AKA The White Ox) because it sometimes sits for several months, then gets used frequently, then sits again. It would require a LOT of cranking to get the fuel back up to the carburetor.

I wired it to only run during cranking, then the mechanical pump takes over, pulling through the electric pump.

I contemplated installing a 'prime' circuit, then decided against it because I feel that it can't hurt to let the oil get circulating a bit before actually firing up.

It only needs to crank 4, maybe 5 seconds at the most before it is running, even after sitting for extended periods.

[Tarheel Blue]

After thinking about all that has been said so far, I felt good enough to order the timer. So now I’m at the stage that has confused me for quite some time, where to tap into my existing harnesses.

Before getting into my areas of confusion I’d like to start with something that I’m guessing might play into the solution.

My truck came from the factory with EEC and I converted it to Duraspark maybe 6 years ago. The EVTM for EEC shows a 3 pole starter relay and that is what is currently installed on the truck, however, the EVTM for Duraspark indicates a 4 pole starter relay with the “extra” pole going to an “electric fuel pump control”

As I see it right now, I have three needs;

A - Hot in RUN
Prior to START for a “X” seconds pause (physically a driver action, pause the rotation of the key at RUN) to trigger the timer which then sends a signal to a relay which runs pump for “x” seconds.

B - Hot in START (after RUN pause) to allow the oil pressure switch to connect ‘S’ to ‘P’ . ‘P’ triggers a relay to power the pump.

C - Hot in RUN (after key spring returns from start) and engine oil pressure is up via the oil pressure switch which connects ‘I’ to ‘P’ until ignition switch is turned off.

I’ve looked at EVTMs for a number of years, including mine of course, and the wiring diagram in the search of which wire/ connector/ fuse to tap into for each of the above needs and I’m as confused as a squirrel in the middle of the road.

Thanks in advance,
Cheers

[Gary Lewis]

I'm confused about the way you are going to wire it.  I thought in Start you were sending power to the pump w/o going through the oil pressure switch.  The switch is only used in Run.  And the timer bypasses the oil pressure switch.  Right?

As for your needs, I think A & C are the same - Hot in Run.  So you really have only two needs.  And in the schematic below you can see where I think you can tap in for those:

Hot In Run: The green arrow shows where I'd get the Hot In Run signal, and that's on the white/light blue wire just before the connector going to the ignition module.  (After the connector the wire is red, but you don't want to connect there as it would make swapping ignition modules hard later.)

Hot In Start: The red arrow shows where I'd get the Hot In Start signal, which is right at the starter relay.  I picked that spot because it is after the neutral start or clutch switch.  But you could also pick the same wire up at the ignition module.

[Tarheel Blue]

What?

You can’t read my mind?


I guess my current train of thought is that I should treat the electrical side of things as two separate entities.


When I first started this project I had a couple of goals to achieve in switching to an electric fuel pump. One was to set things up to be able to run the Sniper TBI in the near future yet still run the YFA until then. The other was that while running the current YFA I could perhaps eliminate or at least greatly reduce the amount of cranking time that it takes to refill the bowl and fire the engine.


So if I were to forget about the whole notion of needing to have a timed priming feature for the moment and just focus on how to wire the fuel pump, I’m faced with two more personal goals.


Whatever connections that I make to the existing harnesses I’d like for them to be as non invasive and as “stock” looking as possible. So your suggestion of tapping into the harness just before or at the C321 connector is much appreciated. Thank you for taking the time to edit a file. Im a visual kind of guy and seeing drawings helps me a bunch.


It seems that your green arrow should then be my green arrow in this diagram.





What I don’t completely understand is from where on this diagram do I connect back to C321 on the truck.  Once I know that, I believe that the truck will run just fine and I would be done with this project.


What I don’t know, and probably won’t until I’ve tried to start the truck a few times after long periods of sitting, is whether or not I even need to add the timed prime feature. Maybe the new electric fuel pump is fast enough to get the bowl filled to where I’m satisfied with how much shorter the crank before firing duration. Maybe because the FDM has check valves in it ( a thought that Pete brought up) the crank duration will be non existent. I just don’t know.

[Gary Lewis]

LOL!  My wife says reading minds is easy, changing them is hard.  But, if you don't change your mind frequently it gets dirty.  

Anyway, I think your wiring diagram will work.  In Start power will connect through the NC contacts on the oil pressure switch, and when the pressure comes up it'll connect through the NO contacts.

As for the question about C321, I think you want to connect the wire going to the inertia switch to the white/light blue wire at C321, as shown below.  That will give you power in Run.

[Les Kerf]

I am confident that your electric fuel pump will get fuel to the carburetor quickly even after sitting for extended periods of time; mine can sit for several months and only requires 4-5 seconds of cranking whereas the stock mechanical fuel pump would run the battery dead before getting fuel up to the carburetor.

Adding a timer circuit creates more complexity than it is worth IMHO.

[Tarheel Blue]

Thanks for that Les.
That is exactly what I'm hoping to experience also and why I've decided to wait a bit on the timer circuit.

So, a couple of last questions,

When Gary says to "connect the wire going to the inertia switch to the white/light blue wire at C321" does that mean that I should do a tap connection to the wire somewhere between the ignition switch and C321 by baring a bit of the W/LB wire and soldering my new wire to it? If so, then where does the wire from the "S" terminal of the OPS (oil pressure switch) terminate?

OR

Cut the W/LB wire somewhere between the ignition switch and C321, connect the switch side of the wire to OPS "I" terminal and then run a wire from the "S" terminal to the DSII side of the previously cut W/LB wire?

[Gary Lewis]

Yes, you want to connect before C321. But I would cut the existing wire at some point where you have slack. Strip both ends of it as well as your wire, twist your wire onto one end of the cut wire, and slip adhesive-lined shrink tubing over that. Solder everything together, pull the tubing down, and heat it up.

The other wire goes to the R/LB wire that goes to both the starter relay and the ignition module. So you can pick it up just ahead of C321 as well, and connect the same way.

[Tarheel Blue]

Thanks Gary, but just to be sure before I start cutting the harness;

How I’m understanding your description would therefore leave both the W/LB and the R/LB wires on the DSII side of C321 not connected to anything?

If that is the case, couldn’t I attach a new C321 male pigtail to the “I” and “S” terminals of the OPS and plug it into the ignition switch side (female) of C321?

[Gary Lewis]

The engine would never fire that way.  You have to have power to the ignition module.

What I'm trying to say is to tap in at the points shown below, in this method:

[Tarheel Blue]

Got it!

Thanks for the help. It might be a couple of weeks, but I will definitely report back once I receive all of my parts orders and get a chance to hook everything up.

[Gary Lewis]