Fuel Pump Cutoff For Carbs Options

[Spoke]

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.

[stugray]

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

[Spoke]

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

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.

[stugray]

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.

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)