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Mar 18, 2021 18:36:55 GMT
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I've bought a longacre oil pressure switch to turn my fuel pump on or off if I lose pressure. It has 2 terminals but I'm assuming it's a live feed in and a wire out to my fuel pump relay. Has anyone used one? Am I right with that? I don't want to short anything out.  |
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1966 Ford Cortina GT
2018 Ford Fiesta ST
Full time engineer, part time waffler on Youtube - see Jim_Builds
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Mar 18, 2021 19:55:06 GMT
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Is it NO or NC?
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j0hn
Part of things
Posts: 58
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Mar 18, 2021 23:58:11 GMT
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Last Edit: Mar 19, 2021 0:03:35 GMT by j0hn
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If it's NO you'll need a momentary bypass to start the car - just to bridge the gap between zero oil pressure and the switch making.
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j0hn
Part of things
Posts: 58
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If it's NO you'll need a momentary bypass to start the car - just to bridge the gap between zero oil pressure and the switch making. Longacre also recommend a bypass for starting in their instructions... This is a 2 terminal switch that is not closed (current flowing) until it senses pressure above 12 psi. Install it somewhere in the oil pressure system and route the power for the ignition system (NOT start function) through this switch. When the oil pressure drops below 12 psi it will shut off the ignition. This is also true for starting. As the starter motor turns over the motor it will not fire until the oil pressure reaches 12 psi (this usually only takes a few seconds). Optionally a user can install a momentary switch across the #43600 shutoff switch terminals (see Longacre #45460 or #45462). To start the motor before it reaches 12 psi simply activate this switch to bypass the shutoff switch. |
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Mar 19, 2021 10:39:05 GMT
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If it's NO you'll need a momentary bypass to start the car - just to bridge the gap between zero oil pressure and the switch making. You could do this by running a feed to the fuel pump that's run off the starter solenoid so it'll run the pump directly so long as the starter is cranking. Depending on how long it takes for oil to get up to pressure there might be a lag between starting and the oil pressure switch coming on though. I know on old Triumph I6s it can take quite a while for them to build pressure. I’ve found that a Golf MK1 GTi fuel pump relay is a great way to solve retrofitting electric fuel pumps and making them safe. It will pulse the pump for 2 seconds (to putting the carb) when the ignition is turned on. After that it requires a constant pulse from the coil (same as a tacho wire) to hold the relay closed and the pump running. If you stall/crash etc. and the engine dies then the pump shuts off automatically. www.heritagepartscentre.com/uk/ac127219-electric-fuel-pump-safety-relay.htmlThese are also called tachometric relays. I've got one in my X1/9 and it works well. |
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melle
South West
It'll come out in the wash.
Posts: 1,983
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Mar 19, 2021 13:56:29 GMT
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For my Saab 96 V4 I've used a brand new OEM Saab 900 fuel pump relay (Saab p/n 9550948) from Saabits, which was a fraction of the price of the Golf one linked above. I've installed a second-hand Jaguar/ Ford inertia switch too for good measure (£5 posted off eBay). |
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www.saabv4.com'70 Saab 96 V4 "The Devil's Own V4" '77 Saab 95 V4 van conversion project '88 Saab 900i 8V
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Mar 19, 2021 15:03:44 GMT
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Thank you all for the advice, I've used an oil pressure switch because I have an oil pressure gauge but no warning light so it's better to cut fuel if I lose pressure to mitigate damage.
I'll try to run a live feed to it, I was worried about it arcing because the switch is mounted to the engine which I'd naturally earthed. I have a no push button to build pressure for cranking but as its a carburettor fed engine there's usually fuel in the bowl? I just found thr long acre instructions a little difficult to understand
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1966 Ford Cortina GT
2018 Ford Fiesta ST
Full time engineer, part time waffler on Youtube - see Jim_Builds
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jamesd1972
Club Retro Rides Member
Posts: 2,835 
Club RR Member Number: 40
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Oil pressure fuel switch jamesd1972
@jamesd1972
Club Retro Rides Member 40
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Mar 19, 2021 21:54:45 GMT
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Ideally you want a couple of seconds to prime the bowl - one of the big advantages of an electric pump over a manual one. On the LR and my old Skoda the fuel vaporises from the bowl on a hot engine making hot starting difficult, electric pump gets rid of this problem.
How about a push switch to prime - horn type just before starting.
James
Oh and push switch to prime would just go to the pump and not the engine.
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Last Edit: Mar 19, 2021 21:56:17 GMT by jamesd1972
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