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Ecu hold power


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On my vehicle the ignition circuit (power on) drops out when key turned to activate starter cranking.  I assumed that this would cause ecu to turn off so i have wired ecu to seperate switch and constant power source.  Ideally i would like to trigger through ignition switch. 

My query - would the ecu hold power function accommodate for this and hold the ecu on whilst cranking and then simply drop back to being "on" when key released from cranking activation. 

Appreciate thoughts and or options

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Thats not really the idea behind hold power. Its supposed to be so you can reset idle solenoids and the like back to zero position. Trying to use it to avoid something like this runs a big risk that if you crank it for too long, the hold power timer expires, and the ECU turns off while its still cranking and you probably wouldnt even notice. 

Better bet would be to re-wire your key output in this case so that the main relay is triggered by IGN1 key pos *and* by start key pos (ie run a wire from the key start position output to the main relay trigger).

Are you sure your ignition circuit drops out entirely when key is at start pos? Ive heard of accessory power dropping out, and in some cases there are 2 IGN feeds off the key and 1 will drop out (for heater, aircon, wipers etc), but in most cases where people think they have this behaviour its actually just voltage drop due to the load being drawn by the starter. 

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What vehicle have you got, and what ecu ?  I am a big fan of hold power from a setup and tuning perspective as the ecu doesn't disconnect eveytime you cycle the ignition (most cars have a one shot crank ignition switch). 

It should work in your application if you set the hold timer to about 10 seconds 




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