Active Engine Disable
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Joined: Oct 2012
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Active Engine Disable
I'm installing a new alarm and it has something like a half mile range and a two-way remote.
I was thinking it would be cool to, in the event that I detected that the car had been entered and the engine started, be able to disable the engine once it was started.
Does anyone have a good wire in the car that I can use with a "normally on" relay that I can trigger to "turn off" from the key fob that would kill the running engine and thwart the thief?
I realize the original alarm had a "starter interrupt"... what I'm looking for is an "engine disable".
Thoughts on what circuit I should disable and the viability of my plan?
I was thinking it would be cool to, in the event that I detected that the car had been entered and the engine started, be able to disable the engine once it was started.
Does anyone have a good wire in the car that I can use with a "normally on" relay that I can trigger to "turn off" from the key fob that would kill the running engine and thwart the thief?
I realize the original alarm had a "starter interrupt"... what I'm looking for is an "engine disable".
Thoughts on what circuit I should disable and the viability of my plan?
Burning Brakes
Joined: Jul 2009
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From: ESCONDIDO CA
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My alarm shuts off the electric fuel pump. If you have a stock pump, it could probably shut down a coil wire.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
I would use the hot wire from the ignition coil to the distributor or module(not sure which one without looking). This way you could use a normally open relay. Have the coil wire T off to the relay and on the other side of the relay have a wire running to the block of the engine.
When the relay was triggered the coil energy would go to the best ground which would be the block and kill the spark to the plugs. It would require a continuous signal to the relay from the remote and a non-keyed power source however, so not sure how that would be done unless holding down a remote button could send a continuous signal.
There may be a relay that once tripped remains in the new position until tripped again and that would work really well. Might want to look around for something like that.
Seems like a normally closed relay would require the same continuous signal, plus power all the time to keep it from opening unless it was spring loaded closed. In either case this could lead to the contacts becoming fused together and when it was really needed the contacts would not open.
It's a cleaver idea. Might be worth looking into.
When the relay was triggered the coil energy would go to the best ground which would be the block and kill the spark to the plugs. It would require a continuous signal to the relay from the remote and a non-keyed power source however, so not sure how that would be done unless holding down a remote button could send a continuous signal.
There may be a relay that once tripped remains in the new position until tripped again and that would work really well. Might want to look around for something like that.
Seems like a normally closed relay would require the same continuous signal, plus power all the time to keep it from opening unless it was spring loaded closed. In either case this could lead to the contacts becoming fused together and when it was really needed the contacts would not open.
It's a cleaver idea. Might be worth looking into.
Burning Brakes
Joined: Mar 2012
Posts: 871
Likes: 73
From: Memphis Tennessee
Get a 5 pin relay like one shown above. Wire ignition coil power in at pin 30, and out to coil at pin 87a. Wire pin 85 to your ignition disable, and pin 86 to ground.
If you wire 87 back to pin 85, it'll keep the relay "latched" and kill power to the coil as long as you have power going to pin 30. In other words it'll kill the ignition till they turn the key to "off" and back on.
If that's not enough, you could run pin 87 to ground and put an inline fuse in the ignition circuit going to pin 30. When you activate your disable, it'll short the ignition circuit to ground and blow the fuse.
