remote fuel shutoff
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=95788
Printed Date: May 14, 2024 at 8:04 PM
Topic: remote fuel shutoff
Posted By: angelars
Subject: remote fuel shutoff
Date Posted: July 20, 2007 at 6:40 PM
The car we're working on ( 2004 Ford Taurus) has a switch located in the trunk for fuel shutoff. The purpose of this switch is to turn off the fuel supply in the event of an accident. The fuel shutoff switch is a simple two wire switch, cut either of those two wires and the fuel would be shut off. The customer wants to use this switch to turn off the fuel supply while the alarm is on. The alarm that he has is a Viper 791XV. Channel 4 of the alarm seems to have a latched output. Is that the best way to add a relay to this switch, or should we use another method? Thanks 
Replies:
Posted By: angelars
Date Posted: July 20, 2007 at 6:56 PM
I should probably also add that he wants this to be completely SEPARATE from the alarms on/off (armed/unarmed) state. That's why we figured channel 4 would be best...
Posted By: angelars
Date Posted: July 23, 2007 at 10:43 AM
Anyone? 
Posted By: KarTuneMan
Date Posted: July 23, 2007 at 10:59 AM
The fuel pump wire is pink/black (POS)+ located in the drivers kick.
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Posted By: angelars
Date Posted: July 23, 2007 at 11:15 AM
Yes we know that, infact BOTH wires are pink/black. How do we know which one goes to the fuel pump and which one goes to the front of the car? They both seem to show voltage when the plug is unpluged. We'd like to avoid having to go under the car, pull the gas tank out, and do a continuity check between the pump and the plug at the shutoff switch...
Posted By: KPierson
Date Posted: July 23, 2007 at 1:33 PM
If there are only two wires at the switch most likely either of them will work (a switch simply breaks a signal). If the customer wants it to be completely isolated from the arm/disarm of the alarm then you would want to use the AUX channel. However, you will run in to problems with battery life doing this, as you will have to use a relay. A better method then 'having the fuel pump shut off when the alarm is armed' is to set it up so that the fuel pump is shut off when the alarm is armed (or aux channel is latched) AND the ignition is on. The car won't start without the ignition being energized, so the system is still secure. Hook the (-) coil to the AUX channel and the (+) coil to the switched ignition signal. Then use contacts 30 and 87A to brake the fuel pump signal. ------------- Kevin Pierson
Posted By: Mad Scientists
Date Posted: July 23, 2007 at 2:09 PM
I'd think about wiring the fuel pump to disable when the alarm is sounding.. I'm not sure if that's what you meant by 'on'. It sounds like you're using a voltmeter to see which wire is hot at the inertia switch - use either a 12v test light (something that'll load the circuit) or use an ampmeter to see which direction current flow is going. Something to consider.. investigate the legal aspects of installing something that can shut down the car like that. A failure in the alarm system might cause the car to shut off, even if it's in the middle of the interstate. I've installed oil level monitoring systems before for large stationary engines.. they caution in the instructions about using in an application that might cause an accident if the engine dies unexpectedly. Jim
Posted By: angelars
Date Posted: July 23, 2007 at 4:14 PM
KPierson wrote:
Then use contacts 30 and 87A to brake the fuel pump signal.
Yes that's what we were planning on doing and then the alarm trigger would be negative latched and the positive of the coil would go to the ignition ( run) circuit. I never understood why people run constant to the fuel cutoff relay because while the car is not running it simply doesn't need the fuel to be stopped. You only need it to work while the engine is running.
I was mostly wondering if using the 'latched' output was the best way to set it up...
Mad Scientists wrote:
A failure in the alarm system might cause the car to shut off, even if it's in the middle of the interstate.
Yes I understand this but the same could also be said if the inertia switch went bad, or if you ran out of gas. I am going to be setting up a similar set up in my car and I am not concerned with protecting someone that wants to do something deliberately illegal against me. There is only around 2-3 minutes worth of gas in the line anyway, and they wouldn't even be able to make it to the freeway. Besides, the car wouldn't just stop in its tracks, the car would studder and then coast and they should be able to get it off the road IF that's their true concern. The gas gauge will also be set up to read empty, so I'm not worried about pampering a thief stealing my car. The car also has 3 separate kill switches so the odds of them getting it are slim to begin with. If anyone was to run into this situation it would most likely be me anyway, as I'll probably forget to turn it off until I get into the habit of checking the fuel gauge ( which will tell me that it's on).
Posted By: Mad Scientists
Date Posted: July 24, 2007 at 8:11 AM
angelars wrote:
Mad Scientists wrote:
A failure in the alarm system might cause the car to shut off, even if it's in the middle of the interstate.
Yes I understand this but the same could also be said if the inertia switch went bad, or if you ran out of gas. I am going to be setting up a similar set up in my car and I am not concerned with protecting someone that wants to do something deliberately illegal against me.
I'm not interested in protecting the thief, I'm interested in protecting myself against legal action.. let me explain it this way. You install this custom modification, the owner of the car goes out driving, the car shuts off and the owner gets into an accident. Because you did this modification yourself, you're legally responsible. Even if it turns out you it wasn't anything you did, you'll still have to defend yourself. Having said all that, if I was interested in doing a fuel cutoff, I'd design it to allow the car to be driven for 5 minutes, then shut down and sound all the lights/horns. Now the thief is in the middle of the road, and is less likely to hang around trying to get the car running again. Jim
Posted By: angelars
Date Posted: July 24, 2007 at 12:11 PM
Mad Scientists wrote:
Because you did this modification yourself, you're legally responsible.
Oh I understand that but I think you missed part of my post  I will be doing this to my car too and the flashing empty fuel gauge will remind me that it's 'on'. The customer is also signing a release form written by our attorney. Plus I forgot to mention yesterday that the car has at least 3 factory relays and fuses that control the same fuel pump. We're in accordance with everything that we can think of :)
Mad Scientists wrote:
I'd design it to allow the car to be driven for 5 minutes, then shut down and sound all the lights/horns. Now the thief is in the middle of the road, and is less likely to hang around trying to get the car running again.
That could scare them and cause an accident too. GPS tracking is the way to handle that. The car will naturally shut down in a few minutes anyway, as there is only that much gas left in the fuel line at the time that it's started. We don't want the theif to think that we wired the car this way, because they could become angry and do deliberate damage to the car. That's why we have the gas gauge read empty with a flashing LED, it will make the thief 'think' that he was just unlucky to steal a car that belonged to someone who was too cheap to fill up  His next instinct will be to get away from the car as quickly as possible when he realizes that the police will be told that the car ' had no gas' in it.
While thinking about wiring the car to ignition I realized that it's not as good an idea as first thought because it will only work IF you turn it on while the car is running. I'm working on a way around this WITHOUT using a constant battery wire.
Posted By: KPierson
Date Posted: July 24, 2007 at 12:26 PM
angelars wrote:
While thinking about wiring the car to ignition I realized that it's not as good an idea as first thought because it will only work IF you turn it on while the car is running. I'm working on a way around this WITHOUT using a constant battery wire.
That is incorrect. If you turn it on while the car is not running the (-) output will turn on, but the relay won't energize. When someone goes to steal the car they HAVE to power up the ignition system, otherwise it won't run. As soon as they power up the ignition system the relay is provided the (+) to go along with the (-) and the relay will energize. ------------- Kevin Pierson
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