Complete Kit - Wiring Harness and MSD EFI question

[Rodster]

I have a Coupe but most parts are the same fro the Roadster. Question: My engine has EFI (MSD Atomic) - the external electric fuel pump is powered/regulated by the EFI computer. (It is a PWM signal, not just "12 volts."

In the Ron Francis wiring harness, there is a pair of wires for fuel pump.

Do I un-plug the tan wire from the RF fuse block/Main harness, and plug the EFI fuel pump wire into there? I do not want to bypass the inertia switch. I have removed the 15A fuse going to the fuel pump.

Is this correct? Any thoughts?

I suppose the "easy" way would be to just not use the RF fuel pump wires and run the MSD EFI fuel pump wires out to the back. . . .

This is what it looks like, the manual does not show this connector. . . .

Thanks.

014.JPG

[phileas_fogg]

I have no experience with the MSD Atomic system, but...

That's exactly what I did with my Holley Terminator EFI; I unplugged the weatherpak & connected it to Holley's fuel pump feed.

With the RF harness Rev N, the inertia switch is wired to the ground leg of the fuel pump relay. Once you unplug the weatherpak, the inertia switch is no longer in the fuel pump circuit. On the Holley system, it was very easy to move the inertia switch to the positive side of the Holley fuel pump relay. I also reconnected the RF ground leg so that I could re-purpose the RF fuel pump circuit.


John

[CDXXVII]

PWM

Pulse width modulation.

You need to run your own wiring. Check your msd manual for suggested wire size. I'm pretty sure what is included in the RF harness will not be adequate.

[GTR750EVO]

Rodster,

I just finished installing the Atomic EFI on my Mustang utilizing a PWM returnless fuel pump which is what I think you are looking at doing. The PWM fuel pump connects to the large orange wire from the MSD Power Module. You should be able to find this on Page 9 of your installation manual if it's the same as mine. Here are links to some (not all, lol) helpful videos that might be worth watching if you haven't seen them already, http://www.maddawards.stream/search/msd-atomic. If you have any more ??, post away and I might be able to help you out.

[phileas_fogg]

PWM

Pulse width modulation.

You need to run your own wiring. Check your msd manual for suggested wire size. I'm pretty sure what is included in the RF harness will not be adequate.

Agree; you need to check the recommended wire gauge. A quick scan of MSD's documentation provides neither a minimum wire size nor a max current specification, so I'd call MSD. Also, make sure that it doesn't matter that the non-powered leg will share a ground with other circuits, or better yet, add a ground at the rear of the car and ground the fuel pump circuit to that.

But I don't _think_ PWM makes the Atomic EFI incompatible with the RF harness in and of itself. At it's most basic, PWM just means the EFI computer turns the pump on and off really quickly so that you don't need a return fuel line (or if you have a return line runs the fuel pump at a reduced duty cycle at idle).


John

[edwardb]

I have a Coupe but most parts are the same fro the Roadster. Question: My engine has EFI (MSD Atomic) - the external electric fuel pump is powered/regulated by the EFI computer. (It is a PWM signal, not just "12 volts."

In the Ron Francis wiring harness, there is a pair of wires for fuel pump.

Do I un-plug the tan wire from the RF fuse block/Main harness, and plug the EFI fuel pump wire into there? I do not want to bypass the inertia switch. I have removed the 15A fuse going to the fuel pump.

Is this correct? Any thoughts?

I suppose the "easy" way would be to just not use the RF fuel pump wires and run the MSD EFI fuel pump wires out to the back. . . .

This is what it looks like, the manual does not show this connector. . . .

Thanks.

I don't have any experience with the MSD EFI, so can't help you there. Including proper wire gauge sizes, etc. But I have used the RF fuel pump wiring for a Coyote install. So can offer this. If you cut the wire shown in this screen grab from the FF Coyote install manual (an older version) and attach your MSD power wire there, the inertia switch relay and fuel pump wires will be connected.



But, since the relay coil and fuel pump power are using the same power source, I'm not sure if the relay is going to like the PWM signal from your MSD setup. My inclination would be to not wire it that way, but (important disclaimer!) I'm no EE. Something to check further I guess. If you disconnect the single pin weatherpack and apply power there, the RF wiring to the fuel pump is used but you'd be on the other side of the relay, so the relay and inertia switch are no longer in the circuit.

[Rodster]

edwardb - YES, this is what I was looking for, and I was thinking of cutting exactly where you did. The connector is in a dumb place, don't you think?

By removing the 15A fuse - this would take care of the battery 12V coming in -- but the diagram in the manual shows the grounds being switched by the relay. I will use an ohmmeter and poke around this weekend.

I need to call MSD and RF next week if I am not able to figure this out.

[Rodster]

John -
Thanks. The PWM signal does not need too much current. . . the MSD fuel pump wire is about 18 gauge. . . so that is OK. I think edwardb and I are on the same track, see below.
-wayne

[Rodster]

GTR75EVO - thanks! I saw some install articles in 4-wheeler magazine, so same info. I will poke around the harness with my meter to see what's what. I may reach out to you later. . . My 302 was built by Engine Factory so it looks like a good performer for my needs (so far)...

[Rodster]

Thanks for the quick reply John!