complex wiring issue(not model specific)

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Thu 15 Mar 2007 20:30
complex wiring issue(not model specific) - track
heres one to tax peoples brains, I nedd to make up a simple circuit that is live when the ignition is on and engine running but will go dead if either the key is turned off or the engine stalls. Im sure there is a way to do it and Im almost certain its something to do using some sort of circuit that is live until and earth is created elsewhere to complete another part of it, thus enabling the simple use of an oil pressure switch. Does anyone know how to do this?

The basis for this is an engine that runs on carbs and single point coil with dizzy. I need to cut the fuel pump in the case of engine stalling etc.
I tried using a relay triggered by the coil's negative but this didnt switch off when the engine cut out, it appears the negative is still live.
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Thu 15 Mar 2007 20:54
complex wiring issue(not model specific) - jc2
On "K" jetronic's made by Bosch the fuel pump was controlled by a relay wired to the distributor;look at a wiring diagram for a vehicle using this system.
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Thu 15 Mar 2007 21:05
complex wiring issue(not model specific) - topbloke
it is called a tachometric relay and was used on mk1 cavalier engines basicaly its a seven pin relay (maybe five its been a long time since i saw one) that needed a trigger from the coil to keep it alive, soon as coil stops fireing, ie stalls, it cuts the fuel pump
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Thu 15 Mar 2007 21:13
complex wiring issue(not model specific) - Screwloose
track

You need a Rover fuel-cutting oil pressure switch. The three pin ones [Lucas SOB 812; fitted to Rover SDi '76-on] have a feed-through circuit that is only connected when there's oil pressure. Run the feed wire to the pump through it.

If you want instant starting before any oil pressure builds [they switch on at only around 7psi] then use a straightforward ballast ignition circuit without a resistor in it as well. A starter-feed switched relay will do.
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Thu 15 Mar 2007 22:55
complex wiring issue(not model specific) - 659FBE
You need to energise the coil of your fuel pump relay from the alternator warning lamp terminal. This will be at about 14V when the machine is charging and at a low or zero volts at other times. The downside of this scheme is that the fuel pump will stop if the alternator drive belt fails.

Do not draw more than about 100mA from this terminal, otherwise the initial excitation and charging performance of the machine will be adversely affected.

659.
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Fri 16 Mar 2007 15:26
complex wiring issue(not model specific) - track
It was previously on a tachy relay, problem was finding another live with engine running to replkace the one that the ecu previously fired up.
Anyway Ive sorted it now, using the oil pressure warning light, when the circuit completes for the warning light, IE no oil pressure or engine stalls the circuit will now activate a relay pulling the power to an open terminal effectively killing the fuel pump.
Thanks for all the advice though.
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Sat 17 Mar 2007 13:49
complex wiring issue(not model specific) - mfarrow
If you want instant starting before any oil pressure builds


With a carb, there should be enough fuel in the float chamber for this not to be a problem. Or pump the accelerator.

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Mike Farrow
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Sat 17 Mar 2007 16:22
complex wiring issue(not model specific) - eastenddoy
ues a five pin relay and use the oil switch as an switch earth and wire the relay contacts back to front ie: turm 30 to fuel pump 37a and 86 to feed 37 to starter and 85 to oil switch
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