Ignition switch power interruption from run to start

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CHARLES FEARNEYHOUGH

CHARLES FEARNEYHOUGH

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Hi fellow Moparians!

I've been running a Sniper EFI on a 1972 LA 360 in a 1967 Dart GT Conv. for the last few years. When I turn the key from start to run there is an interruption of power on the ignition wires. Not a big deal and has been like this forever but it does cause the EFI to reboot. Doesn't cause the engine not to start but I would rather the power remained on during the transition. I have install an ignition relay to reduce the current on the start run circuit and the bulkhead connectors. I have also bought but have yet to install a Hella Time delay off relay that will eliminate the issue but I was wondering if an ignition switch is made for this application that does not drop ignition juice during the transition from run to start. Is there such a beast?

Thank you!
Charlie
 
Stock ignition switch has a make before - brake contacts on the IGN1 and IGN 2.

that should not allow your relay to disengage when going from start to run.

You said your EFI "reboots", doesn't it require a dedicated power source that is supposed to be live 24/7?
 
I was curious if that was not the case. I'll pick up a new switch and see if that does not solve the problem. Yes, the Sniper has dedicated power and ground lines going straight to the battery. The "ign" wire on the Sniper is an enable input to the FI ECU and provides power for the display. Thank you for confirmation on the proper operation of the ignition switch! I do have IGN1 and IGN2 tied together to operate the ignition relay. I didn't mention this before. The ignition relay also enables the MSD.

Charlie
 
It may be your switch is a bit "looser" than others. Lots of us have been doing this with a factory type ignition switch and they work fine, generally.
 
Thank you for your help. I've ordered a new switch. Lets hope the tumbler fits so I don't have to use a different key for the ignition and doors. I guess it really doesn't matter as I never lock this car anyway or leave anything of value in it. I'd rather if someone wants in they just open the door instead of cutting the top.
 
A reverse biased diode, in parallel with relay coil, will freewheel coil current, resulting in slow opening of relay contacts. This is often enough to avoid interruption. Some relays have a built-in diode. It is important to observe correct wiring polarity of coil.

If you have a scope, it is possible to trigger on crank, and observe relay output in capture, with time base set to low frequency.
 
KitCarlson said:
A reverse biased diode, in parallel with relay coil, will freewheel coil current, resulting in slow opening of relay contacts. This is often enough to avoid interruption. Some relays have a built-in diode. It is important to observe correct wiring polarity of coil.

If you have a scope, it is possible to trigger on crank, and observe relay output in capture, with time base set to low frequency.
Click to expand...
Sometimes you can use a cap to "hold" a relay for short period. Use some resistance in series with the relay, and put the cap across the coil. You have to experiment
 
A cap may help, but needs charge time. A quick startup might not provide enough time.

I have a feature to in my ecu to run fuel pump couple seconds, and then shutdown if no engine crank. It purges fuel system. I can tell by sound of fuel pump. If haven't driven for months, will give second prime.

It might be fuel related. That is one reason to use scope for trouble shooting.
 
KitCarlson said:
A cap may help, but needs charge time. A quick startup might not provide enough time
Click to expand...
I just picked these numbers. (If they are close the charge time is negligible)
Screenshot_20220904-065803.png
 
Bosch cube relay relay current is typically 0.11A at 12V that's about 1.3W. A Joule is a Watt second. A guess for required hold time is likely 50 to 150 ms. Using 100ms, requires at least 0.13J. Calculated number above in post 9 is much smaller.

Joule calculation is energy based, assuming discharge to 0V, but more is required to hold relay, perhaps 7V.
 
New switch came today. Quite a challenge to install the tumblers as the tumbler retaining clip would move forward and reposition the clip pivot pin in the wrong place.
I ended up removing the chrome cap from the tumbler and tapping it in with a small drift positioned on the clip pivot. This worked and now the ignition circuit does not drop out! The latch pin on this tumbler does not retract fully into the tumbler. Latch pin and spring are both in their correct positions. It's just real tight. Anyway all is well no need for the time off relay. Vroom Vroom! Opening up the original switch now to see what it looks like inside! :)
 
You can see how worn the contact pads are. The one closest is very worn. Everything was covered in a thick sticky black paste. I didn't bother measuring it for conductivity. I think it actually looks pretty good for its age.

20220904_175103.jpg


20220904_175110.jpg
 
I think you found your problem. That warnout contact was probably making contact intermittently.

Would you post photos of the other side of each part.
 
Maybe the MSD is producing a voltage spike, that shuts down the EFI. MSD make a filter for that, #8830.
 
When I went to EFI on mine, I eliminated the ballast resistor and tied the IGN 1 and IGN 2 wires (blue and green maybe, I can't remember?) together where the connector comes out of the column. I've been running it this way for 7 years with no issues, nothing is getting back fed while it is running.
 
I did the same thing years ago when I went with an MSD CD ignition and distributor. The only difference is the ignition circuits from the key now go to an interposing relay. The ignition switch was the issue. Now if I can only find a driver to tighten the nut on the ignition switch!
 
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