Looks like my mechanical fuel pump is on it's way out so decided that an electric fuel pump is in the SJ's future.
Being an off road toy I wanted to make sure that the fuel pump will only run when the engine is running as a safety feature in the event of a topple over. Came up with this as an idea using a 5pin relay and the stock single wire oil pressure switch.
The pump will only run when the oil pressure dash light is off but I have made provision for a "carb prime" bypass.
Haven't fitted it as yet (job for the weekend) but thought it might be useful to someone else.
Cheers
W
Last edited by Wooky on Fri Sep 28, 2018 8:35 am, edited 1 time in total.
On the race cars that I built and maintained we always had a fuel pump cut-off system fitted. I found it worked best using a RPM signal instead of oil pressure for the switching. The MicroTech system I use on the Toyota 4 AGE motor in my Lotus 7 runs the pumps to prime the system at power up and then cuts the power to them and the ignition system. Only when you crank the motor and RPM signal is detected is power restored to the pumps. On a vehicle with a standard ignition system, I'm sure you can tap off the rev-counter input for your signal. This type of system might be easier to use than an additional oil pressure pick-up system.
The humble person makes room for progress; the arrogant person believes they’re already there.
2004 Disco 2 Td5
I looked at doing something with an RPM pick up but then came up with this idea as a simpler option.
The oil pressure switch is already switching the dash light so all that is needed is the 5pin relay and a push button bypass switch.
Also easy to bypass on the trail if it gives problems
Haven't tested it yet so might well end up going back to an RPM sensing system
There are a few ways of doing this and even a simple angle sensitive mercury switch would do the trick.
I think a lot of the newer fuel injected cars have a g-force sensor included to cut the pump in an accident.
Think you have a problem in your circuit diagram. Your prime switch needs to be after the oil pressure switch. Once your engine starts and the oil pressure switch contact opens you lost the earth connection on your relay and it will shut the pump. You need a pressure switch with a n/o contact that closes on pressure with a prime switch or timer as override start on up.
The 5pin relay has a "Normally closed" and a "normally open" output pin.
The pump runs on the "normally closed" pin on the relay so the relay actually energises to kill the pump.
The prime switch just drops the relay allowing the pump to run.
I run Holley high flow pumps on my three v8 4x4`s with Holley fuel regulators ans rpm engine cut outs. Have bypass circuit to run the pump without interference if needed.
