I'm preparing to install a 2056 dual Weber carb engine in my car and was thinking about how to control the fuel pump. I'll use the existing FI fuel pump relay as done many times before by grounding the appropriate pin on the FI ECU connector to energize the relay with ignition on.

I want to add a safety feature to power the fuel pump only when the engine is running. This is done with all FI systems in case of accident so the fuel pump doesn't keep pumping if the engine has stopped. I want the same functionality with carbs.

I'm designing a PCB to power the fuel pump like DJET systems do: Turn the key on and the fuel pump charges the system for 2 seconds then turns off. When the engine starts turning, the fuel pump will run.

I forsee 4 wires:
GND: picked up on a chassis lug near the relay board
12V switched: Picked up on the FI ECU socket
Relay: Picket up on the FI ECU socket
Coil Neg: This goes to the tach as well.

The coil negative would be the signal to indicate engine running.

Should I consider any other functionality of the fuel pump controller? Anyone interested in a PCB like this?

Does a 2 second precharge do anything for a carbed engine? I could see if the carb bowls were not full but other than that, not sure a precharge does anything.

Get a fuel pump relay for an early fuel injected VW Rabbit. Five pins with a built in fuse, relay energizes when it see's the engine cranking from the coil signal. No real need for a 2 second prime with carbs unless the float bowls are empty. The relay stays energized for a few seconds after cranking so a few blips with the key would fill the bowls without extended cranking.

Mallory (Mr. Gasket) used to make a switch that works via oil pressure. It had two contacts, NO and NC. I wired a fuel pump to it so it would cut off the pump with loss of oil pressure.

Fitting is 1/8" NPT, which would thread into the oil pressure hole on the top of the case, but you would loose your oil light unless you used a hose and tee to run all the switches.

The oil pressure idiot light is a on/off switch. You should be able to use that to control the relay ...

Get an inertia switch for a collision cut off.

What you are looking for is a pulse detector circuit that is watching the Tach signal.
What kind of dizzy & Ignition are you running?

With a Mallory optical pickup & a MSD 6AL I have a variety of signals to look at:
Clean 0-12VDC square wave from the Mallory to the MSD (I also send this into my datalogger)
0-12VDC square wave into the TachAdapt from the MSD
0-400VDC tach-like signal from the Tach Adapt to the stock Tachometer.

If you have just the stock ignition (or a pertronix) driving the coil directly then you only have the coil (tach) to trigger off of.
You can build a relatively simple circuit to hold a relay closed if this is pulsing using a filter and a transistor

VW/Audi early 80s CIS fuel pump relays used tach signal and shut down the pump if the engine stops. They also have a 2-4 second priming cycles when the key is first turned on.
They also have a rev limiter built in that cuts off the fuel pump when rpm reaches about 6500 rpm or about 8100 rpm if you used a 5 cylinder relay on a 4 cylinder engine.

Jim

Jerry,
When you figure it out count me in.

Part number 321 906 059 C

Early relays do not have a fuse, late and aftermarket relays do have a fuse.

Connections

15 = 12v key switched
31 = ground
87 = main power (direct from battery)
30 = switched power (fuel pump+, put a fuse in-line here if needed)
31b = coil negative, tach output

I agree. I think running a fuel pump without an automatic cut-off is, how should I say it, ... not smart...
Just use a relay like in this post.

http://www.914world.com/bbs2/index.php?s=&...t&p=1535731

The engine has Pertronix Ignitor so it's a classic ignition. You hit it, I'll build a circuit to monitor the tach signal. I want to make the PCB so it can be plugged into the FI ECU socket.

The goal is to add the circuit without cutting any vehicle wires and make it look good. There's only 2 wires needed including ground and the tach signal. Not sure where to pick up the tach signal other than at the coil.

The tach signal passes thru the engine compartment relay panel on the way from the coil to the tach.
Black and violet wire I believe, not sure which pin in the 12 pin connector.

Jim

I built a circuit based on the Tach pulse detector in the megasquirt.
It had a couple of large voltage zeners that would only conduct when the coil was spiking (>21V I think), then that fed an Opto circuit that fired to give me a reasonably clean signal to input to the microcontroller.

Simplest would be to just have a RC circuit that is charged when the coil is firing, but self discharges.
Then an op amp (or a singe BJT) could release the coil winding when the RC voltage drops below a threshold.
Just make the relay self-latching when the ignition is turned on and the engine is being cranked.
and the pulse detector opens the winding circuit when it is "triggered".
You could make it bleed relatively slowly to avoid false positives but it might run a few seconds after engine off.

OH and I have an arduino small enough that it would fit inside a relay module....... they cost $9 each, but you need +5V (if you want to get fancy)

Well, I ended up with an RC circuit. Actually 2 RC circuits. But it isn't very simple.

I thought I had a circuit that works then I simulated the circuit with LTspice and it failed miserably. This is 2nd circuit and it seems to work.

Whatever ICs I used I want them to be 25V+ tolerant so I don't have to create a lower voltage. So I focused on using comparators. The main timing is C1 and R3. This is a 2 second delay used for key-on and after the engine dies.

Comparator U1D senses when the starter is engaged and shorts C1 to ground turning on Relay driver Q1.

First comment is make sure your design can handle +400V spikes on the input at a rate of RPM /30 (6000 RPM = 200 Hz).

It almost looks like you built a 555 Timer circuit yourself out of discrete components.
I will take a closer look, but first glance looks like more components than necessary.
My circuit based on this kind of megasquirt circuit after I added a 555 timer IC to the output had fewer parts.
I set the timer circuit in monostable mode to stretch the short tach pulse that made it through the optocoupler for detection by a microcontroller.

The exact same "pulse stretcher" could be used to hold a relay closed such that if a pulse was not detected for ~3 seconds it would open the relay.

I have to look for the circuit and the notes.
When I changed to a Mallory with an optical module and a MSD, I didnt need the circuit anymore as I used the output of the optical sensor.
It is a nice clean 12VDC square wave.
No need to protect from 400V spikes, so I tossed it in the back of a drawer somewhere.

http://www.summitracing.com/parts/sum-890145
This is what I used on my six conversion. Easy wiring and installation.

That is on my list for the race car to shut off the FP in the case of an accident.

It wont stop the FP if the engine just stops though.

Here's a circuit with a 555. Simpler than the previous circuit even including a 10V LDO to limit the voltage to the 555.

And still, my single relay circuit does the same job but its much simpler.

If you insist in using a pulse detector using 555 or discreet comppnents, add an AC component to the power supply in your spice simulations, as well as a voltage increase/drop that is RPM dependent. This will make your simulations much more interesting.

Your power supply doesn't seem.robust enought.

Also, do you have a parasitic capacitance in the clamping diode model? Guess what that does to your circuit, especially when you have a voltage undershot from the coil.

I can't see why all this work?
Is it just to keep the relay on the board?
Again why? It's carbed so it's not like it's concours.

The relay Valy posted works on oil pressure, the the relay I posted uses a simple tach input, both could be quickly stealth installed without a single OEM wire cut...so I don't get it?

Sometimes the challenge of reinventing the wheel proves irresistible!

Keep in mind that I am an engineer and it's the engineers code to solve any problem in a manor such that the problem didn't need to be solved in the first place and to make the solution so complicated that no one can figure it out.





Yes the relay is already there and want to provide the bit of protection that shuts the pump off when the engine stops. I want to be able to switch from carbs to FI easily. This circuit will mount in the FI power connector on the relay board with one wire going to chassis and the other to the coil.



Just having fun with electronics.



Again, fun with electronics. Here's a board I just finished for my 3d printer. It is an LED ring that will fit right inside the carrier to illuminate the work. Could have bought a generic LED ring for $30 but this one is more intricate and fits beautifully on the printer. Theirs has 6 LEDs and mine has 8 LEDs so mine is better.

You're not true to your signature: "CSOB of PA"

I remember designing similar elaborate circuitry, but then I had to write documentation so our field engineers had a road map for troubleshooting. Then I had to write additional documentation allowing normal folks to operate the device(s).

Glad I'm retired now

Here's a first cut at the PCB and the FI plug. I can shrink the board a bit. Right now the entire assembly is a bit over 2 inches tall.

Here's a simpler circuit which interfaces to the oil pressure switch to sense engine running. I think I'll add an LED to indicate the pump is powered.

Here's the layout of the oil pressure fuel-pump cutoff. Should have the board back in 2 weeks. Shrunk the board to 0.6in x 0.7in. It's tiny.

Got the boards back. Gotta order a few parts then assemble and test. As I mentioned before, they are tiny.

Oh, when you said they were going to be really tiny - I was thinking like, smaller than a dime

The power FET and catch diode pretty much determined the size of the board. I used 0603 sized resistors which are best soldered when using a microscope.

Well we'll see how much this adventure costs. I like to stay true to form.

I've already got $2.10 invested for the PCB alone; That's for 3 PCBs; Including shipping.

Very nice there Jerry. I would be interested in one of these if you decide to sell them

Thanks

David

That's a Ford inertia switch. I installed one on my LS1 conversion car. Make sure it's readily accessible in case you get bumped. Ford placed them in all sorts of weird places that were difficult to get to. On my Explorer, it was high up under the right side dash, on the Supercoupe, it was in the trunk.

Andys

the whole thing has got very complicated and don't really see the point of making it to hard,bypass wired is the known method from FI to carb works is good enough,if you crash and we do ,you turn the key off......simple really.
We are looking @ a low pressure supply afterall not a biggie,cheers.

BJ's 6 conversion caught fire when the fuel pump kept running after he turned off the key. Better safe than sorry.

Got the Ford inertia switches for both my cars- installed one on the '73- didn't any instructions but luckily mounted it button up as I now see on their catalog page.

If you got that route, definitely get the wiring plug as it makes installation a snap.

Can kind of use as a theft device but pushing the button in to turn off power to the pump.

Never be complacent with what is available. I enjoy the challenge of designing and building things.

Why buy these for $5 total...

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When I can buy this for $35 and have some real fun...

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