Lotus Elan

Oil Pressure Cut off for electric fuel pump

PostPost by: nwbaxter66 » Tue Feb 06, 2018 3:22 pm

I am in the process of installing an electric fuel pump along with the cut off switch designed to stop the pump when engine stops.
Does this oil pressure sender replace the existing sender that is feeding the oil pressure gauge or is an additional sensor?
is there one brand of sensor that people have had success with?
If it is additional, where does one normally install it?
Thanks for your assistance.
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PostPost by: oldelanman » Tue Feb 06, 2018 4:19 pm

Have a look at the description for this switch - it may answer your questions ......
https://www.demon-tweeks.co.uk/Product. ... es&gclid=C
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PostPost by: prezoom » Tue Feb 06, 2018 5:05 pm

You may need a bypass switch to prime the carbs if the engine has not run in a while. Otherwise you will have to crank the engine to get oil pressure to energize fuel pump.
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PostPost by: Chancer » Tue Feb 06, 2018 6:27 pm

I prefer to use a type that is triggered by the HT pulses of a running or cranking engine, to be exact its a relay that is triggered by the resultant voltage transients on the LT circuit, many early fuel injected cars had them as standard, the Ford Escort XR3i being the one I know of and whose relay I have used.

You get the safety without a seperate over-ride switch which may inadvertently be left on.
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PostPost by: nwbaxter66 » Tue Feb 06, 2018 6:31 pm

Very helpful.
The alternative might be to run a crash sensor/relay to the pump?
Two solutions to similar but not identical scenarios.
thank you for the suggestions and advice
N
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PostPost by: nmauduit » Tue Feb 06, 2018 7:14 pm

nwbaxter66 wrote:Very helpful.
The alternative might be to run a crash sensor/relay to the pump?
Two solutions to similar but not identical scenarios.
thank you for the suggestions and advice
N


yes, I have put one of these in series when I recently installed an electric pump in my road elan : in case of a crash but with the engine still running (hence oil pressure) the fuel stops being pushed to the bay 30 gallons per hour (the cutoff via a relay from low oil pressure signal has not been wired in yet).
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PostPost by: billwill » Tue Feb 06, 2018 7:51 pm

I drew a suggested circuit in this topic:
lotus-carbs-f40/electric-fuel-pump-noisy-idle-t20354-15.html#p117904

Image

It uses the existing oil pressure warning switch (ON when no oil pressure) with a relay to operate the fuel pump, it will make the fuel pump stop if there is no oil pressure, so there is a push button for priming the initial fuel to the carbs). Push buttons can't get left on by forgetfulness.
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PostPost by: mbell » Tue Feb 06, 2018 8:10 pm

I've also fitted a fuel cutoff switch on my car and have the elec fuel pump and electronic ignition powered via it. So if it's triggered by an impact it will kill the engine instantly and fuel supply. I also plan to add a fuel cut off solenoid at some point to prevent any fuel flow from the tank.

The only advantage I can see to having it triggered by oil pressure rather than fuel cutoff switch is it will prevent the pump running when the key is left at run but the engine isn't running. Which for me isn't a concern as shouldn't be leaving the car key run with engine not running due to risk of over heating coil and electronic ignition module.

Personally if the concern is to kill the engine if the oil pressure drops I just fit a loud buzzer in the cabin. Stopping the fuel pump won't kill the engine instantly as engine has to burn the fuel in the carbs. It could leave you unable to stop in a safe location thou, which could put yourself and the car in serious danger. A loud buzzer makes sure you are aware and leaves you the choice in how to handle the situation should it arise.
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PostPost by: rgh0 » Thu Feb 08, 2018 10:55 am

In a Plus 2, even one with a mechanical fuel pump, a fuel cut off solenoid valve at the tank outlet is a good idea. The high mounted tank with bottom off take will continue to flow if the carbs, pump or line into the engine bay have a problem and feed a fire. Dont ask me how I know :evil:

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PostPost by: Quart Meg Miles » Thu Feb 08, 2018 11:22 pm

A drawback of the oil pressure method is that the Elan can lose oil pressure on sharp right hand turns if the oil level is low. Then you have to press the pump-start button again, once the pressure has restored itself, assuming that you noticed the flashing warning lamp (which early Elans don't have as standard).
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PostPost by: billwill » Fri Feb 09, 2018 12:25 am

Quart Meg Miles wrote:A drawback of the oil pressure method is that the Elan can lose oil pressure on sharp right hand turns if the oil level is low. Then you have to press the pump-start button again, once the pressure has restored itself, assuming that you noticed the flashing warning lamp (which early Elans don't have as standard).


No I don't think so, with my circuit above, a momentary loss of oil pressure has a momentary stop of fuel pumping, but there should be enough fuel in the carb bowls to survive until the oil pressure is back and the pump electricity is back on automatically.
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PostPost by: Quart Meg Miles » Sat Feb 10, 2018 10:25 pm

billwill wrote:
Quart Meg Miles wrote:A drawback of the oil pressure method is that the Elan can lose oil pressure on sharp right hand turns if the oil level is low. Then you have to press the pump-start button again, once the pressure has restored itself, assuming that you noticed the flashing warning lamp (which early Elans don't have as standard).


No I don't think so, with my circuit above, a momentary loss of oil pressure has a momentary stop of fuel pumping, but there should be enough fuel in the carb bowls to survive until the oil pressure is back and the pump electricity is back on automatically.

You are right, of course! I had been thinking that once the pressure dropped it would latch the fuel pump off permamently, but a running engine will simply restore it. I was confusing it with my own design, not yet implemented, which would latch the priming button until the oil pressure rose and then de-activate it. From a few weeks standing it takes a while for my pump to fill the carbs.
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