Fuel Pump Cut off / Safety if Engine dies

In another thread it was mentioned that with mechanical pumps it is a fact that when the engine stops so to does the pumping of fuel. With electric pumps you get less cranking at start up (fuel evaporated) but if the engine dies the fuel can still be getting pumped out at a high rate.

I will be running Efi with 2 pumps and cross over valve - when selector switch is clicked over right to left the only fuel gauge will pick up from the other tank.

So how could this setup work if I wanted it to "die" with the engine? Presumably on the oil pressure switch through a relay (to allow for current required for 2 pumps)

BUT hod do I get the thing to start as wothout electricity no fuel pump, end up cranking engine to get oil pressure to activate the fuel pump but by then the battery will be dying! (possibly need a press button t prime the pumps before cranking???)

Can anyone do a wiring diagram that could cope with this? Or am i worrying unnecessicarily for nothing?

thanks
Ian

Ian

Get Paul to look at the wiring diagram of the Rover that I gave him it also had a low oil pressure fuel cut off.

Hope it helps

Geoff

Geoff

thanks for that I'll have a look - I just can't figure how the pump would be primed / run before oil pressure builds up

Thanks
Ian

Wire up a manual over-ride?

Ian, if the engine dies on a crank fired electronic ignition the injectors won't be injecting fuel per the ECU's instructions. The fuel pump might run, but it'll simply be returning the fuel to the tank, so nothing to be concerned about.

You might want to fit an inertia switch that will cut the fuel in case of an accident where the motor is still running, for a short time, but the fuel lines are ruptured. This would keep fuel from spraying all over. These are OEM type switches and are on all modern FI cars, thus easily obtainable.

They also, in my experience, don't go off on track days with normal track driving unless positioned wrong. Even with an off - it takes a good high g shock to trip them like you get in a crash.

Chris
Yes a manual overeride is good but will it create havock with the Efi circuit / put electricity where it should not be? It will obvoiusly turn off the Oil pressure light and then "energise" other parts of the circuit / s / blow ecu etc.
I am not a sparky and cannot see the electrons so don't know what will happen! My logic says the override will end up feeding all the circuits and avoid the need for a key - yes the override button neds to remain pressed to keep the engine running but it could be wedged in to on position by a thief! (I adnit to robably not thinking it through straight)

Ron
Yes the safety / accident cut off sounds good and will probably get fitted after SVA - I am more worried about the HP fuel line spraying fuel - engine dying but the pump still running because the ignition is on. 40GPH on low pressure and 100\LitresPM quickly makes a big puddle of fuel!

Ian

Ian, if the injectors aren't energized by the ECU to fire they won't spray fuel, even if the pump is on. So, if you have your car on ideling away, and I come over and pull the plug wires, the pump will run but there won't be fuel puddling anywhere.

A cut off switch will solve the issue of an accident in which your HP line is cut. The switch in an accident will turn the pump off.

Ron

Hi Ian

If your HP pump(s) are fitted with non return valves on their output, the system will require virtually no priming at all. I have had systems hold 45 Psi for quite some time after switching off. (beware if you need to 'open' the fuel rail for maintenance). You could possibly use a feed from the starter solenoid exciter to power the pumps relay. Fitted with an approriate diode, there would be no reverse feed either.

BUT - before you do any of these do you know for sure you need to?? - 'most' electronic EFi systems power the HP pump(s) for a short period to prime and then switch off. As you crank, the pump(s) start again and IF the motor should die, for whatever reason, the pump(s) are dutifully turned OFF by the ECU. On a MOTEC system, all these time parameters are programmable, but I would think most systems would do something similar by default. I wired a Cosworth Turbo powered track car for Ray Christopher last year and whilst someone had already wired pumps to dash mounted switches, I rewired it accordingly with the Weber Marelli ECU, using the appropriate output to control the pumps as detailed above. Much Much safer in the event of a 'heavy off'. ANYONE and EVERYONE running EFI with fuel pressures of 45Psi or more should take the time to see how much fuel these high pressure pumps flow if the output is left open to 'free flow', believe me it's like a hose-pipe!! /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/blush.gif

I don’t know how your ignition/starter switch is wired, but you can energize the fuel pump relay, bypassing the oil switch, from a connection to the starter switch or button. The relay isolates the starter solenoid from the fuel pump.
John

Ian
I don't know if this would help, but I have seen a valve that is actuated by engine vacuum, commonly used on forklifts with LPG. It is used to stop fuel flowing if there is no engine vacuum present. Just an idea that I thought was good.
Cheers
Phil /ubbthreads/images/graemlins/twocents.gif

Guys

thanks for the info - a pile more reading for me.

Paul I think i'll start by checking the Range Rove loom / ecu set up as you say this may already be built in

thanks again

Ian