Do I need a diode or a new brain?

[Tarheel Blue]

I thought that I could figure this out on my own, but I was wrong!

As many of you know, I’ve been working on the installation of a Bronco tank and electric fuel pump. I completed everything and re-installed the bed the other day.

I’m very pleased with the outcome except for one issue. I had hoped that the electric fuel pump might shorten the cranking time it takes for the engine to fire upon rotation of the key to START.

NOPE, no change. It still takes forever and it drives me nuts!

Here is how everything is wired up.

The * is hot in RUN (W/LB)and the $ is hot in START (R/LB)

Descriptions for X,Y and Z will be explained below.

Yesterday I ecided to install a momentary switch to run the pump (thus re-filling the bowl) and I’d be happy.

So, I connected the switch between Y and Z in the drawing . . . .

NOPE, when the key is in the RUN position and I press the new prime switch, the damn starter engages!

Scratched my head, had a cold one, sat around in a miserable mood all night etc.

This morning I decided to find a spot in the fuse box that would give me hot in RUN. I installed the switch between fuse location 15 and Z on my drawing. Thought I was a genius until . . . .

Key in RUN, press the switch and the damn starter engaged again.

Am I getting back feed? Is a diode needed? Where am I going wrong?

 

[Gary Lewis]

I'm sorry, but I get lost in your schematic. But why not do it as shown below? It would pull the fuel pump relay in when the key is on and the button is pushed, thereby priming the carb.

[ArdWrknTrk]

I'm not sure why you would need a leg of your momentary switch feeding into the "$tart" side of the ignition module?

The pump should be getting full power (around the resistor and oil pressure switch) with the starter engaged.

But if you're looking to prime the carb before you turn the key I would do like Gary shows and just pull in the fuel pump relay momentarily.

 

[Tarheel Blue]

I'm sorry, but I get lost in your schematic. But why not do it as shown below? It would pull the fuel pump relay in when the key is on and the button is pushed, thereby priming the carb.

Sorry about that. After looking back at the drawing that I had used, I realized that it could use a couple more labels. See if this helps

As to your suggestion, that approach is basically what I did in my first attempt. BIG difference tho, I don’t have any of those wires in my truck.

I have this;

Also, a quick reread of https://forum.garysgaragemahal.com/Definitive-way-to-wire-an-electric-fuel-pump-for-a-Pre-EFI-Bullnose-tp108879.html should refresh memories of the help provided back in December.

I took that approach and everything turned out perfect, I’m simply trying to add a manual prime feature.

[Gary Lewis]

Sorry about that. After looking back at the drawing that I had used, I realized that it could use a couple more labels. See if this helps

As to your suggestion, that approach is basically what I did in my first attempt. BIG difference tho, I don’t have any of those wires in my truck.

I have this;

Also, a quick reread of https://forum.garysgaragemahal.com/Definitive-way-to-wire-an-electric-fuel-pump-for-a-Pre-EFI-Bullnose-tp108879.html should refresh memories of the help provided back in December.

I took that approach and everything turned out perfect, I’m simply trying to add a manual prime feature.

Ok, I reread the post to which you linked and I like that diagram. And if you have wired it that way then the push button switch should prime it like you want. Also, wired that way it can't cause the other problems you are having. So I'm guessing that it really isn't wired that way.

Have you checked to see that it is exactly as shown?

[ArdWrknTrk]

Ok, I reread the post to which you linked and I like that diagram. And if you have wired it that way then the push button switch should prime it like you want. Also, wired that way it can't cause the other problems you are having. So I'm guessing that it really isn't wired that way.

Have you checked to see that it is exactly as shown?

He could just wire the switch around the relay (30 to 87)

That would leave 86 completely isolated from any chance of back feeding the starter.

[Gary Lewis]

He could just wire the switch around the relay (30 to 87)

That would leave 86 completely isolated from any chance of back feeding the starter.

Yes, that would work - if it is wired as shown in the diagram. But jumpering 85 to 86 would also work - if it is wired as shown. I think there's some error in the wiring because if it is wired the way the diagram shows then jumpering across the oil pressure switch can't power anything else.

I think there's a change in the wiring to the pump, not the trigger wire of the relay. And if I'm right, then jumpering 30 to 87 will also cause the problem.

[ArdWrknTrk]

Yes, that would work - if it is wired as shown in the diagram. But jumpering 85 to 86 would also work - if it is wired as shown. I think there's some error in the wiring because if it is wired the way the diagram shows then jumpering across the oil pressure switch can't power anything else.

I think there's a change in the wiring to the pump, not the trigger wire of the relay. And if I'm right, then jumpering 30 to 87 will also cause the problem.

I'm just not seeing anything on X of the green diagram or in the above between 87 and the fuel pump.

85 to 86 would bypass the pull-in coil, and depending on resistance, probably keep the fuel pump from ever getting power.

A diode could solve it. But it depends on where the circuit is tapped

[Gary Lewis]

I'm just not seeing anything on X of the green diagram or in the above between 87 and the fuel pump.

85 to 86 would bypass the pull-in coil, and depending on resistance, probably keep the fuel pump from ever getting power.

A diode could solve it. But it depends on where the circuit is tapped

I was wrong! I should have said to jumper around the oil pressure switch, as shown in the diagram but not across the inertia switch. NOT across 85 and 86, which will do nothing.

I think what I'd do is to temporarily install a pushbutton switch across the oil pressure switch, push it with the key on and everything clear of the fan, and see what happens. I think the starter will engage as somehow things are connected to the R/LB wire going to the starter relay. That's just a guess, but that's my guess.

If it tries to start then jumper from 30 to 87 with the same switch and see what happens when you push it. If it tries to start the issue is on that side of the relay. If it doesn't try to start the issue is on the oil pressure switch side of the relay, which I think is impossible - unless there's another wire from 86 on the relay going some place else.

[85lebaront2]

I was wrong! I should have said to jumper around the oil pressure switch, as shown in the diagram but not across the inertia switch. NOT across 85 and 86, which will do nothing.

I think what I'd do is to temporarily install a pushbutton switch across the oil pressure switch, push it with the key on and everything clear of the fan, and see what happens. I think the starter will engage as somehow things are connected to the R/LB wire going to the starter relay. That's just a guess, but that's my guess.

If it tries to start then jumper from 30 to 87 with the same switch and see what happens when you push it. If it tries to start the issue is on that side of the relay. If it doesn't try to start the issue is on the oil pressure switch side of the relay, which I think is impossible - unless there's another wire from 86 on the relay going some place else.

What I used to do on Darth, just never got around to adding a push button, was to take the blue fusible link off the starter relay's small stud and touch it to the battery side post on the relay until I heard the "hiss" from the vapor separator telling my I had filled the float bowls.

A push button connecting battery power to that point will run whichever pump (or the only pump) as long as it is held in.