Car starter voltage drop to efi

Thread Starter

Gotf

Joined May 18, 2023
3
Hi all. I have connected my starter signal wire to my efi unit so that i am able to control fuel,timing, and air while the vehicle is cranking.

The efi supports a 12v input (single wire lead from starter) to use as a signal of sort to allow me to specify how I want it to behave. The input is considered ‘on’ if voltage is greater than 4.5 volts. I have observed that during cranking the efi input will show as off momentarily (10th of a second) randomly.
Is this something I could addres with a capacitor? What type? What size? If so, suggestions for how to wire? Thank you.
 

Hymie

Joined Mar 30, 2018
1,284
Adding a capacitor to the efi 12V supply (of suitable value) should solve the problem, but you will also need a diode in circuit to stop the capacitor being discharged by the starter motor load.

Given that it can operate correctly down to 4.5V, I’d try a 1,000µF capacitor with a 1N400X diode. To ensure a long life of the circuit, use a capacitor rating of at least 25V, and avoid the circuit being within the engine bay where elevated temperatures will shorten the life of the capacitor significantly.
 

LowQCab

Joined Nov 6, 2012
4,075
No wire, from any Fuel-Injection-Computer, should ever be connected to the Starter.
Start-Mode is determined by RPM, not a separate Voltage-Input.
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Thread Starter

Gotf

Joined May 18, 2023
3
Adding a capacitor to the efi 12V supply (of suitable value) should solve the problem, but you will also need a diode in circuit to stop the capacitor being discharged by the starter motor load.

Given that it can operate correctly down to 4.5V, I’d try a 1,000µF capacitor with a 1N400X diode. To ensure a long life of the circuit, use a capacitor rating of at least 25V, and avoid the circuit being within the engine bay where elevated temperatures will shorten the life of the capacitor significantly.
thank you so much. Would something like the following work:https://www.amazon.com/McIgIcM-1000...00+microfarad+capacitor&qid=1684420207&sr=8-5

Also, are there ‘boards’ or something I can solder the capacitor and diode to and then connect that unit to the wires to improve serviceability? I’m concerned if I connect these components in line with my wiring and have to replace them that I’ll run into issues.
 

ElectricSpidey

Joined Dec 2, 2017
2,786
This is something I would use a relay for.

Let the starter connection drive the relay coil and let the relay contacts provide a cleaner connection to the battery.
 

crutschow

Joined Mar 14, 2008
34,468
Let the starter connection drive the relay coil and let the relay contacts provide a cleaner connection to the battery.
I would think the "starter connection" is a signal derived from a switch to the starter solenoid with a direct connection to the battery, so not clear that a relay would help.
 

Thread Starter

Gotf

Joined May 18, 2023
3
No wire, from any Fuel-Injection-Computer, should ever be connected to the Starter.
Start-Mode is determined by RPM, not a separate Voltage-Input.
.
.
.
Thank you. I’m trying to manage an issue where my VR Magnetic distributor gives the efi invalid readings while cranking (low rpm). The efi is given momentarily an rpm value that the efi determines as car running. Although the rpm value does it correct the efi is already in run mode , which causes issues getting a proper start.

any ideas on how to get a more stable rpm signal at low values from a VR Magnetic distributor?
 

LowQCab

Joined Nov 6, 2012
4,075
Is this a Manufacturer-Installed Computer ?,
or an Aftermarket-Computer ?, ( Brand & Model Number ),
or a Home-Made-Computer ?

What type of Engine are You working on ?

How do You KNOW that there is a Distributor-Signal problem ?

Why are You NOT attempting to solve the Distributor-Signal problem ?
Any Distributor-Signal problem is very likely to cause other problems,
completely aside from cranking-problems.

Please describe the starting problems that You are experiencing, in detail.

Exactly
how will your "unusual-solution" solve the starting problems You are experiencing ?
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shortbus

Joined Sep 30, 2009
10,045
This has to be a home made thing. EFI is done using crank and cam positions from sensors on those things, crank and cam. The starter motor would only come into the problem if the battery volage drops very low when cranking, low enough to disable the ECM.
 
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