givemethebighammer
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| posted on 6/5/04 at 11:21 PM |
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Would this work - fuel cut off circuit
Been thinking about how to cut the fuel off in the event of an accident came up with this:
Using a changeover relay wired in parallel with the oil pressure warning lamp. Whilst the engine is stopped and the ignition is on, the lamp is lit,
the relay is feeding power to pin 87 which is connected to nothing. When the engine is started the oil pressure lamp goes out and the relay switches
the power to pin 87a which feeds the fuel pump. Power to both the lamp and the relay are both fed from the ignition side of the fuse box (only live
when ignition is on). A bypass switch is wired in parallel to the relay to provide the ability to prime the carbs or as a "get you home
measure".
Picture below should help. Only question now is what amp rating of relay to use.
 
Rescued attachment fuel cut off.JPG
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Hasse
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| posted on 7/5/04 at 05:41 AM |
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Can´t see why not.
Any "normal " mini-type relay will do.
Don´t think the fuel pump will need more than max 10A.
Don´t use to big a relay, cause the current needed to operate the coil will be switched by the oil pressure switch, which may not be designed for very
high currents.
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givemethebighammer
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| posted on 7/5/04 at 12:46 PM |
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I have a 20A changeover relay is this too big ?
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A Badger
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| posted on 7/5/04 at 12:53 PM |
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Why not add a bypass circuit that is wired into the starter button/key, so whilst the starter motor is turning there is power to the fuel pump.
Though thinking about it this will happen anyway after a few turns cranking, so ignore me.
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blueshift
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| posted on 7/5/04 at 03:53 PM |
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you don't want to wait for the oil pressure to go high before you start your fuel pump. all the car wiring diagrams I've seen that
incorporate oil pressure switches into fuel pump control have it set up so that the fuel pump runs while the starter is running OR the oil pressure is
high.
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MikeRJ
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| posted on 7/5/04 at 08:36 PM |
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Most production cars have a timer that briefly runs the fuel pump when you turn the ignition on, just to pressurise the injection system.
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givemethebighammer
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| posted on 7/5/04 at 09:37 PM |
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I'm running carbs so I hoped that there would be enough fuel in the carb bowls to get the engine started. If not I could prime the carbs with
the manual overide switch.
The idea behind my circuit was that in the event of an accident the engine will have stopped but the ignition could well be still switched on. No
sense in pumping more fuel into an area already at risk of (if not already) on fire. The oil pressure thing seemed the obvious answer.
People seem to agree the theory looks OK however I am looking for potential problems I might experience in reality
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