# Electric Fuel Pump Prime Switch

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#### Deve

Joined Dec 28, 2015
95
I just posted this article and it explains what I am trying to do in detail:
http://forums.devestechnet.com/foru.../1845-tip-of-the-week-53-for-october-2-8-2016

The idea is that on vintage vehicles, the carbs fuel evaporates (or drains backwards) after a few days or weeks of sitting there and makes you have to crank the starter longer to get it started. To eliminate this problem, an electric fuel pump behind the mechanical one (for redundancy) and a momentary switch in the cabin for the operator to depress for a few seconds before starting. Now, I am thinking is there a way we can make that 5 second priming action happen without the operator having to depress the switch? Before you call me a dummy, understand the electric pump goes through an oil sensor switch to prevent it from spewing fuel all over the place during an accident. So no oil pressure, no workie. Solutions anyone?

#### tcmtech

Joined Nov 4, 2013
2,867
Personally, I have never wired an add on electric fuel pump for a carbureted system to anything but direct ignition so that it was always on when the key was on.

The way I see it is if you're in a wreck that was so bad the carb gets busted off or fuel lines are cut there is probably a whole lot more damage that has been done to the fuel and electrical systems anyway that negates the point of the oil pressure interlock needing to shut the pump power off. Also if it upside down the fuel is probably going to drain the tank fill line and the pump itself can't draw off the bottom of the tank since the fuel is no longer there either.

The only thing I use oil pressure interlock for is ignition cutoff to shut the engine down in the event of low oil pressure which is a multiple magnitudes of order more likely event to happen to an older engine that being in firey crash where fuel system shutdown is of value.

BTW. I read your link and ethanol is not the problem with our fuels. Its designed to rot regardless of whether ethanol is int or not.

Here's a link to a thread in another forum where I elaborate on the real problem and what needs to be done to get around it. http://www.redpowermagazine.com/forums/topic/103557-another-reminder-on-todays-gasoline/

I know were the real problems come from and have adapted to those issues so I run E30 or higher blends in everything now and have no problems with it and by everything I literally mean every vehicle and engine powered device or machine from my string trimmers and chainsaws up and I have no better or worse issues than everyone else who does not.

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#### #12

Joined Nov 30, 2010
18,210
Modern cars turn the pump on with the ignition switch, therefore, they don't depend on having oil pressure.
The whole, "flaming wreck" scenario is handled with a g-force switch.
Bump a grocery cart in the parking lot and the fuel pump shuts off.

#### wayneh

Joined Sep 9, 2010
16,402
Bump a grocery cart in the parking lot and the fuel pump shuts off.
Really? I had no idea. Any idea when this became common, if it is? It actually does make sense to turn the fuel pump off after an airbag deployment. Why not?

#### shortbus

Joined Sep 30, 2009
8,057
Another solution looking for a problem thread. If you want a vehicle that works like a new one, buy a new one. The guy's that want old/antique vehicles today for "status symbols" and don't want to or don't know how to keep them in running condition are a joke. * Rant over.*

#### Deve

Joined Dec 28, 2015
95
Always someone isn't there? Some of us drive these old vintage trucks as our daily drivers. Making them more reliable is what it is all about. So far there has been ONE helpful post. Can we do better or is this just a social site and helping someone figure out an electronic solution is something we just talk about?

So far, the inertia switch makes sense and was a great suggestion. I am looking for discussion about solutions here folks. Solutions are all that matters. Idiotic banter is a waste of time. Can we get on the same page here? The only problem with the inertia switch solution is the price. Rockauto is my main source for parts like this because usually they are the cheapest. For repeatability, we need a source that stays up over time and the switches need to be new. $60 for the switch is a bit pricey. I am hopeful for a 10-20$ max solution. Cheaper if possible.

So once again, is there a small circuit we could build cheaply that runs the electric pump for X seconds then goes back to the oil pressure switch on startup? I mean this is unreal folks! Have we fallen so far as a society that all we can do is either criticize others work or just muck up the threads with nonsensical crap that serves no-one? Where are the moderators when an intelligent question is asked and an intelligent answer is expected? I mean REALLY? This forum is THE premier forum for this sort of thing... or WAS it?

#### #12

Joined Nov 30, 2010
18,210
* Rant over.*
Yeah, that was a bit of a rant, and a little severe in my opinion.
What we have here is a person who set himself up on the Internet as some kind of guru.
So he comes up with this modification and doesn't know how to make it do all the things he wants it to do.
But it's already published in half-baked form.
My opinion is, if you want a primer pump, use a momentary push button so it only runs when the driver presses the button.
"But I want it fully automatic with all the safety features of modern cars."
Then design it like a modern car. Use a G-force switch for the safety shut-off function.
There is no amount of 555 timers, PIC microprocessors, or Arduinos that can beat the G-force switch for simplicity or reliability.
If you want people to bet their life on your design, use parts that are certified for that purpose, not some cobbled together hobby project.

#### Deve

Joined Dec 28, 2015
95
Nothing 'Guru' about me.. just a person interested in providing solutions. You know, that thing that happens when people collaborate and work together to find just the right answer? Inertia switches are 1990s technology and not the be-all, end-all. If I wanted a way on a vintage carbureted vehicle that turned on the electric (non standard, yet OEM) pump for 5 seconds, then shut off to rely on a much more stable oil pressure sensor, how would we do that? It's not rocket science and it does not require a bunch of discussion about half baked, cobbled together, or half baked anything. What we DO need is a discussion on the original post and how to go about it. Is there anyone left here that is interested in the subject or are we just going to talk it to death? If I knew so much as to be a GURU, I wouldn't be asking for help! HELLO?

#### djsfantasi

Joined Apr 11, 2010
6,975
An 8 bit PIC. Thats your answer. More than that we might have to get into details.

#### tcmtech

Joined Nov 4, 2013
2,867
It's not rocket science and it does not require a bunch of discussion about half baked, cobbled together, or half baked anything. What we DO need is a discussion on the original post and how to go about it.
Okay so a homemade discombobulated timer circuit based on oil pressure control retrofitted to an older vehicle is okay yet the totally passive inertia switch that has been standard issue on every fuel injected vehicle for 30+ years now that at worst needs its reset button pushed to make it go again is an unreliable impractical concept?

Yea I see how we are mistaken on how the design problem is in fact on our end.

You came here for help with something you don't quite know how to implement. The problem is when you have access to the brains and life experiences of many people who are knowledgeable in the subject matter you're not the odds are that they are going have far different ideas and reasonings on how to approach the issue than you and your limited knowledge and reasoning has came up with.

#### Deve

Joined Dec 28, 2015
95
As far as I know if you pull it yourself a inertia switch might be free at auto salvage yard being it one item they never pull to recycle being they typically never fail. If not one would probably be under $10 if the pulled it for you. Maybe thinking OUTSIDE of the box would help? I can't get into anyone else's head, but seems to me going to the easy, already tried solution leaves out the possibility there is something better for this particular application? Okay? #12's idea was out of the box. What more do you want and why? It's a cheap, easy to work with, reliable, passive device that's built to do exactly what you need. There's nothing more to say. Solution found. #### inwo Joined Nov 7, 2013 2,419 Connect the fuel pump thru o.p. switch as it was. Add a line thru a diode to fuel pump from starter circuit. #### inwo Joined Nov 7, 2013 2,419 Or from aux. contact on starter solenoid if present. "I" terminal. Thread Starter #### Deve Joined Dec 28, 2015 95 Thanks inwo.. is there a particular diode that would be better for that? I was thinking timer circuit, relay, etc but don't know enough on how to go about it. If anything fails, I want it to fail to where nothing happens until the oil pressure sensor takes over for safety. The reason the inertia switch is not ideal is twofold: We are talking about 1940's through early 1960's vehicles. Since the carburetors are designed so primitively and the carb's float shutoff valve is fragile at best, we do not want constant pressure on it. We want it only to be stressed when it has to be, just like GM designed them when they put in the mechanical pump. You can get away with running it all the time, maybe. I do not come up with this stuff alone, I do research and call my expert friends who advise me what works and what doesn't. Like I wouldn't put an electronic circuit together without asking the experts here, I wouldn't propose a change to the fuel system without asking the experts there. The other reason it isn't ideal is because when you put kits together for people, you do not want to estimate the cost to them every time you make a kit. One week Ebay will have them used for$10. The next week someone else purchased all the cheap ones and now they are \$40 or more. That is all moot anyway due to #1 above.

Please try to stay focused. Research has been done, decisions are made based on research and science. It has been common practice to use oil sensor switches on these vintage vehicles when changing over to electric or augmenting with electric because they are reliable. I was just thinking that having an automatic circuit for priming might be nice. Others thought so too, so here we are. Now, my hope is we can bring THIS forum back to the way it used to be when you asked about a solution, and several guys chimed in with HELP.

http://www.devestechnet.com/Images/Projects/ElectricFuelPump/FuelPumpSchematiclg.jpg

#### inwo

Joined Nov 7, 2013
2,419
How much current does fuel pump require?
If a couple 100ma then 1N4000 series 1amp diode. If more use 1 diode from a common common 25a bridge.
Or try running thru the 1N4000 and see if it gets hot. It's only "on" a minute during cranking til oil pressure comes up.

#### inwo

Joined Nov 7, 2013
2,419
Just looked at attachment now.
If you use low side control of fuel pump and high side signal from cranking circuit, you will need to add a transistor to the circuit.
Then B+ will pull fuel pump neg. to B- while cranking.