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Do I need a diode or a new brain?

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Tarheel Blue

Do I need a diode or a new brain?

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?

Kurt K
'85 XLT Lariat, 4.9L, NP435, 3.08LS, DSII, 130a 3G, PMGR, '87 MC, P235/R75

Gary Lewis

Re: Do I need a diode or a new brain?

Administrator

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.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

In reply to this post by Tarheel Blue

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.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Tarheel Blue

Re: Do I need a diode or a new brain?

In reply to this post by 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.

Kurt K
'85 XLT Lariat, 4.9L, NP435, 3.08LS, DSII, 130a 3G, PMGR, '87 MC, P235/R75

Gary Lewis

Re: Do I need a diode or a new brain?

Administrator

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?

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

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.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Do I need a diode or a new brain?

Administrator

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.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

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

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Do I need a diode or a new brain?

Administrator

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.

Gary, AKA "Gary fellow": Profile

85lebaront2

Re: Do I need a diode or a new brain?

Administrator

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.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

I think the issue here is that this system (DS-II swapped AND an electric fuel delivery module in a Bronco tank) is using the (I) terminal for spark retard, and that is back feeding the (S) trigger.
I've been told the 300 never had an electric pump until EFI.

At first I had suggested the (I) terminal, but reconsidered that suggestion and deleted half my post.

There's little any of us can say without actually seeing all that's going on, as Gary is angling for.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Tarheel Blue

Re: Do I need a diode or a new brain?

In reply to this post by Gary Lewis

The last two suggestions are what I was trying to describe as my attempts in my first post. My wiring is exactly as shown in your last diagram. The oil pressure switch is a three pole. The description of its function is; Terminals P and S are normally closed, terminals P and I are normally open. When oil pressure reaches 2 - 4 psi, P and S are opened and P and I are closed Continuity testing has proven this to be true, so I’m assuming the switch is good.

I temporarily inserted the push button between P and I ( the left and right terminals in my diagram) and with the key in RUN, the pump ran but so did the starter. Thinking that I must be getting feedback to the start circuit through the oil pressure switch( terminal S), I decided to run “clean” power to the trigger of the pump relay (from battery to terminal 86). Starter still engages when pressing the prime button.

This is the point at which I thought of a diode as a fix/ bandaid, would still like to know why it seems to be needed. Something ain’t right.

Kurt K
'85 XLT Lariat, 4.9L, NP435, 3.08LS, DSII, 130a 3G, PMGR, '87 MC, P235/R75

Tarheel Blue

Re: Do I need a diode or a new brain?

This is the jumper/ splice that I made to insert the prime button.

The orange wire comes from the push button which gets its power from my unused fuse 15
The R/LB wire comes from the P terminal on the oil pressure switch
And the blue wire is the relay signal wire 86

Just did another test by disconnecting the R/LB wire from the splice and the pump runs w/o the starter engaging, so I must be getting feedback via the R/LB wire.

I know very little about diodes. If I were to install one on the R/LB wire, are there size/ amp/ ohm/ etc. considerations when purchasing?

Kurt K
'85 XLT Lariat, 4.9L, NP435, 3.08LS, DSII, 130a 3G, PMGR, '87 MC, P235/R75

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

You would want a rectifier diode, and if you're only using it to pull in the relay even 1/2 W should be okay.
You need to place it at the R/Lb wire before the splice.
The symbol for a diode appears like an arrow hitting a wall. This shows which way the current will flow.
The diode itself will likely be marked with a band close to one end to indicate 'polarity'

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Tarheel Blue

Re: Do I need a diode or a new brain?

Thanks Jim!
In a quick search for 1/2 w rectifier diode, I have two questions.
W= watts? Or W= wave?
Rectifier seems to indicate changing from AC to DC?
What does that do for me?

I guess a third question. Would you see any issue if I were to place the diode between the ignition switch and the S terminal of the oil pressure switch?

Kurt K
'85 XLT Lariat, 4.9L, NP435, 3.08LS, DSII, 130a 3G, PMGR, '87 MC, P235/R75

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

A rectifier diode as opposed to a Zener, Light Emitting, or other kind of diode.
They are somewhat optimized to minimize drop in the forward direction while not breaking down if overloaded against the gate.

Diodes by nature will only allow current to pass in one direction. To rectify alternating current you need to create a bridge of diodes. Half wave rectification will only pass the peaks of a sine wave while a full wave bridge rectifier (4 diodes) will invert the valleys giving you a constant series of peaks (kinda like whoops on a dirt track)

So a rectifier diode -in your case- will block your momentary switch from triggering the starter.

Get a diode rated at a minimum higher than your electric system should ever see. Say 18V... or more!

I'm trying to reply from the mail client on my phone. I can't see your picture ATM but I will revisit this thread when I get back from lunch.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

ArdWrknTrk

Re: Do I need a diode or a new brain?

Administrator

In reply to this post by Tarheel Blue

In this diagram?

You say P & S are normally closed, so you will be powering both if you switch I to either of them....

Like I said above you can simply run your switch across 30 & 87 of the relay.
This would power the fuel pump without affecting anything downstream on the trigger side (86 in this case)

Now that Radio Shack is dead I don't know any place locally to purchase "onesies" of any electronic component.
My suggestion would be the ubiquitous 1N400x series diode. These range from 1N4001 (@100V) to 1N4007 (@1,000V)
Any of this cheap and cheerful diode series are more than needed.

They all have a 1A rating and a forward drop of ~0.7V, which is fine with a regular Bosch style cube relay.
(In fact I can get a 12V cube relay to pull in with the stator output of my alternator that approximates 7V)

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Tarheel Blue

Re: Do I need a diode or a new brain?

Installed a 1N4001 diode today placing it in an in-line mini fuse holder for protection in the engine bay.

Key in RUN, push the momentary contact switch and the fuel pump comes on WITHOUT the starter engaging.

Tomorrow I need to run some tests to figure out how many seconds it takes to fill the bowl in the ol’ YFA so that I can get a good squirt or two out of the accelerator pump so that she starts without a lot of crank time.

Kurt K
'85 XLT Lariat, 4.9L, NP435, 3.08LS, DSII, 130a 3G, PMGR, '87 MC, P235/R75

Gary Lewis

Re: Do I need a diode or a new brain?

Administrator

Excellent!!!

Gary, AKA "Gary fellow": Profile

BigBrother-84

Re: Do I need a diode or a new brain?

In reply to this post by Tarheel Blue

Happy for you that problem solved!
This reminds me why I LOVE my mechanical pump...

Jeff / 1984 F350 Crew Cab 4x4/5.8L w351 4V/ T18/ D50 4.10 front/ 8' bed.
Restored 2019-2022.
Nicknamed «Big Brother 1984», due to its soooo-looong shape & nod to George Orwell's 1984 famous novel.