12v+ Power only when engine is actually running
Thread Starter
On The Tree
Joined: Sep 2009
Posts: 114
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12v+ Power only when engine is actually running Does anyone know if there is a circuit that can be used to tell when the vehicle is actually running? I am trying to wire in a safety mechanism to avoid cranking while the engine is running.
Thanks in advance!
Thanks in advance!
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TECH Apprentice
Joined: Jul 2016
Posts: 349
Likes: 19
How about using a 5 pin relay.
Fuel pump trigger wire to 85, ground to 86.
Put a 1A diode inline with pin 85 so it doesn't put a load on the PCM
wire. Starter (switch side) to pin 87a and starter output to pin 30.
87 is unused.
The starter circuit will remain connected until the fuel pump is running,
then it will be interrupted.
This is assuming the fuel pump trigger is +.
My thought is that I would probably use an oil pressure switch instead.
Because the fuel pump will power up when you turn it on for a few seconds (so you'll have to wait to start it, and the fuel pump trigger will be on while it's trying to supply fuel at startup.
So, now that I think about it, it probably won't work like you want.
My guess would be that an oil pressure switch would throw a ground, so you'd do oil pressure switch output to 85, and ignition to 86.
Only one relay should be required.
Jay
Fuel pump trigger wire to 85, ground to 86.
Put a 1A diode inline with pin 85 so it doesn't put a load on the PCM
wire. Starter (switch side) to pin 87a and starter output to pin 30.
87 is unused.
The starter circuit will remain connected until the fuel pump is running,
then it will be interrupted.
This is assuming the fuel pump trigger is +.
My thought is that I would probably use an oil pressure switch instead.
Because the fuel pump will power up when you turn it on for a few seconds (so you'll have to wait to start it, and the fuel pump trigger will be on while it's trying to supply fuel at startup.
So, now that I think about it, it probably won't work like you want.
My guess would be that an oil pressure switch would throw a ground, so you'd do oil pressure switch output to 85, and ignition to 86.
Only one relay should be required.
Jay
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TECH Addict
Joined: Oct 2016
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From: PDX-OR-USA
If you use an oil pressure switch You can get oil pressure before the engine fires,,, then it will stop cranking. Whether its really running or not.
I'd use an RPM switch set to right below idle RPM.. So once its running long enough to idle it would lock out.
I'd use an RPM switch set to right below idle RPM.. So once its running long enough to idle it would lock out.
Thread Starter
On The Tree
Joined: Sep 2009
Posts: 114
Likes: 0
How would the engine know its cranking on startup? In my mind it shouldnt start fuel until it knows its running. The two second prime on ignition is for startup.
I guess i need to find out what triggers the pcm to turn the fuel pump on after the initial prime.
I guess i need to find out what triggers the pcm to turn the fuel pump on after the initial prime.
TECH Apprentice
Joined: Jul 2016
Posts: 349
Likes: 19
When you turn the car on, it turns the pump on for a few seconds to build pressure. Then it shuts off. When you crank it, it will turn the fuel pump back on as it's starting and should remain on while it's running.
RPM switch is probably the best idea of the 3.
Jay
RPM switch is probably the best idea of the 3.
Jay