# Electric Fuel Pump Prime Switch

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#### inwo

Joined Nov 7, 2013
2,419
IMO it will prime fast enough while cranking if fuel pump comes on before oil pressure.
The simplicity makes it worth 5 sec of cranking?

#### inwo

Joined Nov 7, 2013
2,419

#### inwo

Joined Nov 7, 2013
2,419

Might get a little more time with this by hitting crank momentarily before starting.

#### GopherT

Joined Nov 23, 2012
8,012
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.
It's a joke. That's what, "" means.
What do you mean "it's a joke"?

All vehicles with electric fuel pumps have had cut-off switches for a long time. The reset switch is generally located inside the trunk or hatch just foreword of the fuel filler door. Remove the trim piece or access panel and the switch is directly screwed to the support steel.

For added fun, the Explorer's reset button resets the radio presets and clock as well.

#12

#### tcmtech

Joined Nov 4, 2013
2,867
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.
<impolite language removed by moderator>

I too work with engines of that erra as well and I disagree all way around. If the electric fuel pump put out the same PSI as the old mechanical one the carburetor has no way of knowing how or what is producing the pressure.

Also if there is now an electric fuel pump in the system then the mechanical one is redundant and not needed. Get rid of it. It's serving no purpose.

Just because a bunch of people think alike does not make them smart or right unless they have actual scientific and technical proof to back their claims up and from what I can see so far everything you are talking about sounds like standard issue tinkerers cobbling things together work not properly analyzed and engineered concepts.

The way I see it.

1. Many of those old mechanical fuel pumps rant at 3 - 6 PSI so if the electric pump is in the system and it puts out the same range of pressure they carburetor is seeing exactly what it needs.

2. The system now has two fuel pumps making one redundant. Being you want auto prime and the electric one dies that whereas the mechanical one does not, getting rid of the mechanical one seems pretty obvious.

3. Cost issues. BS. A decent quality electric fuel pump costs about $40. A good use inertia switch is under$20 and there are thousands of them available online at anytime making the possible 'limited availability and price 'excuse void.

4. I don't know of anyone who drive a 1940's - 1960 vehicle as a daily driver unless either they are dirt ass poor which I doubt being keeping vehicles of that age running is not cheap or they are well of and it's fully restored and modernized to properly and safely handle daily driving in modern traffic conditions.

5. As I pointed out before in an earlier post, any vehicle of tht era that is in a a bad enough crash to warrant needing full fuel system shutdown has already taken on enough damage that there is far greater issues to be dealt with. One being the driver most likely being dead or mangled for life.

6. If the accident is that bad then maybe tieing the inertia switch in to shut the whole electrical systems down would be a added bonus as well.

7. Kit cost. BS. If a person can afford to run and maintain such a vehicle they can obviously afford to buy the parts new not second hand.

My take is more than likely you want this designed for one of your own vehicles and the are no others who do.

My practical experience with people who collect vehicles that era strongly says you're trying to BS us to get someone to design something for you which if you are planing to make them into saleable kits means you are now liable for an malfunctions that may happen with your homemade DIY systems which for one if the timer circuit fails and keep the pump on all the time will have both the electrical and mechanical running in series which could either push the float valve off its seat lead into at minimal flooding the engine or pumping raw gasoline out of the carburetor all over the engine leaving a high potential for a fire.
Also there is just as much likelihood that the added inlet pressure could rupture the mechanical fuel pumps internal diaphragm and seals thus flooding the engines oil with gasoline leading to catastrophic engine damage.

Just because this is an electronics forum does not mean no one here has any practical experience in anything else in life. Many of us are highly diversified and educated in fields far beyond just hobby level electronics work. I for one am very experienced in mechanical service and troubleshooting work which included first hand knowledge and experience dealing with fuel systems of all forms including do ign fuel pump refits an all out fuel systems redesigns for old equipment not just of my own but for others who both collect and use their stuff as regular daily work machines.

You came her for advice and we give it. The down side is most of use see things in a larger view and can easily see where there are or there is the potential for one thing to negatively affect something else. That and we are not stupid or inexperienced in reading between the lines regarding what other say they want and why either and when someone takes given advice and questions defensively and give what can easily be seen as weak excuses that raises red flags for many of us that whats being presented id no where near the truth and thus that why you're getting hassled.

#### Deve

Joined Dec 28, 2015
95
Please stop. I stopped reading your idiotic tirade at about the first BS. Are you providing solutions or are you just flapping your yapper? Go ahead and answer, we all know. Meanwhile, the idea is to get immediate starting so priming needs to happen before cranking. Does anyone here know how to make SW-1 in the diagram happen at hitting the IGN switch for just a few seconds before cranking? Some of the guys have 6 volt systems and cranking is limited in the first place. We could just mount a momentary on the dash, but that is why I came here. To see if THE PREMIERE forum for all things electronics had someone who knows. Thanks inwo for trying, but I really want to prime the system prior to cranking. Any ideas?

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

#### inwo

Joined Nov 7, 2013
2,419
If you need activation for a set time from "ignition on" use an off the shelf interval timer.
Anyone on here could help design one. I don't know why the reluctance. It wasn't always this way.

#### Deve

Joined Dec 28, 2015
95
I know. I have been here for a long time and never seen anything like it. No-where did I ask for help in designing the fuel system. The entire issue is stated in the original post. We have gone from people calling other people dirt poor to coming up with all sorts of excuses as to why a lot of people who have collaborated on this design is stupid. The system is not up for discussion. That has already been hashed and rehashed to death on other forums who specialize in automotive fuel systems among many other things. THIS forum is for how to accomplish the electronic portion of the puzzle. I am absolutely flabbergasted at the unbelievable resistance there is here in just helping others solve these supposedly fun problems.

Since nobody on the other forums mentioned an inertia switch, turns out for good reason, but I didn't know, I was happy someone helped at least try to make a difference. That is two people who have made any effort to help. Everyone else? Special place for you my friends. Wasting everyones precious time and I have NO idea what you are getting out it, but it needs to stop. I would hope the moderators could come up with some rules for this sort of thing. On MY forums you get by with this kind of crap for about 1 jet second. Shame on you.

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

#### inwo

Joined Nov 7, 2013
2,419
To make your own circuit, use a 555 timer.
It would need to be inverted differentiated input from ign. switch driving a transistor to fuel pump.
Look up "inverted monostable".

#### inwo

Joined Nov 7, 2013
2,419

#### #12

Joined Nov 30, 2010
18,210
What do you mean "it's a joke"?
The "parking lot with a shopping cart line" is a joke. Isn't it?
See post #3.

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#### GopherT

Joined Nov 23, 2012
8,012
The "parking lot with a shopping cart line" is a joke.
See post #3.
I thought you meant the idea of a g-force triggered cutoff switch was the joke.

#12

#### wayneh

Joined Sep 9, 2010
16,401
Me too. That's what I asked about, not the shopping cart comment. I honestly didn't know about g-force switches involved in power to the fuel pump. I wonder when they came into common use.

#12

#### Deve

Joined Dec 28, 2015
95
Prior to 1995 I can't find any reference to them, so about then. I had no idea either. Meanwhile, I am looking at using a relay to make break the power line on IGN so that in its relaxed state it always defers to the condition of the oil pressure sensor. It's probably not that easy, but that is the rabbit hole I am checking out right now.

#### GopherT

Joined Nov 23, 2012
8,012
The inertial switches came in with fuel injection and electric fuel pumps. Filling a float bowl was easy with a few psi of fuel, fuel injection needs 35 to 55 psi (typical) so the electric motors were added and the issues were addressed essentially as EFI was rolled out.

#### inwo

Joined Nov 7, 2013
2,419
Prior to 1995 I can't find any reference to them, so about then. I had no idea either. Meanwhile, I am looking at using a relay to make break the power line on IGN so that in its relaxed state it always defers to the condition of the oil pressure sensor. It's probably not that easy, but that is the rabbit hole I am checking out right now.
Then it would always bypass oil switch when ign. is on.
Unless it's an interval timer relay.

#### Deve

Joined Dec 28, 2015
95
Yes, very useful information. Thank you. I am thinking if I use a relay and a timer circuit it should work as planned. The book you referenced is very helpful. I have never built a timer circuit before so it's all new to me. Ebay circuits are cheap, but I like to build these things myself so I have more control over the supply chain. I need to make sure the design is such that if it fails, the behaviour of the fuel pump is that it only comes on when oil pressure is present.

#### inwo

Joined Nov 7, 2013
2,419
The inverted mono 555 circuit (from book) has a timed output pulse to fuel pump only once. When ign. is first turned on. It then stays off until ign. circuit is turned on.
It only fires with a change from low to high.
The output is enough to drive a tx or small relay.
I would buy a 555 timer/relay kit on Ebay and modify it.

#### inwo

Joined Nov 7, 2013
2,419
For fail-safe a td undersized fuse from timer to PS. bypass will blow after xx seconds.

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