Relay for fuel pump shut off

[Ken Heaton]

I recently installed an electric fuel pump on my Series III. I think it would be wise to add a relay that would shut off the fuel pump if the engine stopped, like in an accident so it would not continue to pump fuel. Has anyone had any experience adding a relay to a Series engine for such a purpose?

[Rob P]

Adding the relay should be easy, the hard part is finding the trigger mechanism to work the relay. I would start by contacting a speed shop or somewhere like Summit racing and tell the you need a controller to shut off your fuel pump in a crash or rollover. If such a sensor outside of OEM is available they should be able to source it.

[Ken Heaton]

I was hoping to use an existing sensor, tonight I will see if I find one on the engine that will work.

[Rob P]

Summit has one here: http://www.summitracing.com/parts/SUM-890145/ but buy the socket also. Relay and socket together are around $30.

[Ken Heaton]

I called Summit Racing and talked to their tech support, they did not recommend that inertia switch for my vehicle, apparently it has to connect to a computer to shut down the fuel pump (Series III's do not have computers, ;).) What they did recommend was a Low Pressure Cutoff Switch that can be piped into the port for the original low pressure signal light, that was only $16.95 anyway, so I bought that instead. You have to install an 1/8 inch tee to connect the original low pressure signal switch and the new cut off switch.

[Rob P]

So I take it that when the oil pressure goes away while the key is in the "on" position the fuel pump will be shut off. Wondering to myself how long it takes to do so. Cranking engine requires fuel and might not makke enough pressure. Same goes for stalling on the trail, would you have to reset this thing each time?

I am glad you found something that will work though.

[siiirhd88]

The oil pressure switch has one set of contacts that are closed when oil pressure is present. If oil pressure goes away, the contacts opens and the fual pump stops. The switch has a second set of contacts that close when the starter is cranking, supplying power to the fuel pump only when the starter is turning. When the key is released after start, the contacts open... At that point there should be oil pressure.

The wire from the ignition switch to the starter soleniod is white with a red trace. You can just run a wire from the solenoid connection to the terminal on the oil pressure switch.

I would supply power to the fuel pump via a relay. To limit current on the oil pressure switch I would run the relay actuation wire to the oil pressure switch and then to the fuel pump relay. When cranking the fuel pump relay would be actuated by the wire coming from the white with red trace wire on the solenoid.

Bob

[Rob P]

Ah, I see. ( Moment of enligbtenment)

[Ken Heaton]

So I take it that when the oil pressure goes away while the key is in the "on" position the fuel pump will be shut off. Wondering to myself how long it takes to do so. Cranking engine requires fuel and might not makke enough pressure.

That is a good point, I am actually installing a bypass switch that will turn on the fuel pump and allow the engine to start and build up oil pressure. After the engine is running, then the bypass switch is turned off. This is actually recommended by Summit Racing in the instructions for the installation.:cool:

[Ken Heaton]

I would supply power to the fuel pump via a relay. To limit current on the oil pressure switch I would run the relay actuation wire to the oil pressure switch and then to the fuel pump relay. When cranking the fuel pump relay would be actuated by the wire coming from the white with red trace wire on the solenoid.

Where do you get these relays? I am having a hard time locating one.:confused:

[rvrsrvc]

I like the idea of having a low oil pressure cut off for the fuel pump- used it all the time on the race cars and it saved an engine on the Ginetta.
But I am wondering if this isn't too complicated. What if you were to integrate an inertia switch from a Discovery into the power side of the fuel pump? It's a 2 wire connection- put it inline for the 12v ignition wire currently being used to power the pump. Mount it vertically anywhere that's convienent.
I've got a few in the parts cars. I'll send you one with the check for the seat shipping and you can check it out.
Plus it would be utilising Genuine Land Rover parts!

Errgh! I can't find you business shipping address!

[Ken Heaton]

I like the idea of having a low oil pressure cut off for the fuel pump- used it all the time on the race cars and it saved an engine on the Ginetta.
But I am wondering if this isn't too complicated. What if you were to integrate an inertia switch from a Discovery into the power side of the fuel pump? It's a 2 wire connection- put it inline for the 12v ignition wire currently being used to power the pump. Mount it vertically anywhere that's convienent.


I have to admit this whole low pressure cutoff switch is getting very complicated. (But then again, I like complicated) My shipping address is:

Ken Heaton
Lehigh Cement Company
7660 Imperial Way
Allentown, PA
18195

I will mount it on the bulkhead, then I will have all kinds of protection.

I still want to get the speakers and Tuffy boxes installed once I get everything sorted out with the fuel system. I also want to look at the 95 Disco I, I like those early models. What kind of shape is it in?

Ken

[rvrsrvc]

I'd say it's in very good condition relative to the miles. I've serviced it since 2005 and the current owner has had it since 2007 when he bought it from Art Pursel. It has a new clutch last October, front pads and rotors, regular services, a new serpentine belt tensioner all within in the last few months. Current inspection good through October 2010. 147k Dark blue over tan.
It was crashed last fall and I fitted a used hood, LH fender, grille, lights after cutting away the mangled brush bar. No structural damage, just cosmetics and apanel replacement. I've heard that the son had another minor fender bender at the front and I don't recall detail but it wasn't bad. He's still driving it.
I've asked the owner to send some pix of the car for reference.

[Ken Heaton]

I need a beater, I know what body shop not to send it to!!

[Rob P]

Now I haven't looked yet but either Radio Shack (AKA the cell phone hut) or Pep Boys should stock 12volt coil single pole or double pole relays. Ask for a 12v spst relay or get fancy and give youself more options in the future by getting a 12v dpdt (double pole double throw) relay.

[Ken Heaton]

I talked to one of my electrical engineer colleagues at work and he directed me to this website: newark.com. They sell thousands of these things, I got an 80 amp normally open 12v automotive relay for $3.25.

[siiirhd88]

I usually pick up relays from the electrical rack at a generic auto parts store. They are just a 30 or 40 amp relay with four male spade connections, main power in, switch power in, main power out and ground. I've found the ones with a metal mounting tab to be more durable than the plastic mounting tab relays.

For the fuel pump, the switch power in wire would come from your bypass or the oil pressure switch.

You can mount the oil pressure switch or pressure senders on the wing or bulkhead. I use a flexible line for a grease gun to go from the oil filter housing to the wing, where it usually attaches to a brass 'T' fitting. I braze or solder a flat mount to the brass 'T' to bolt it to the wing. The flex line has 1/8" pipe thread on each end, and is rated for pressure much greater than your Rover oil pressure. The flex lines come in various lengths are are far cheaper than trying to buy a specific flex oil pressure line. Just remember that it will take just a bit longer to pressurize up to the switch or sender....

If you do use a bypass switch for startup, use a momentary pushbutton or toggle switch so it can't be left in 'bypass'.....

Bob



Where do you get these relays? I am having a hard time locating one.:confused:

[rvrsrvc]

I drove by the-body-shop-who's-name-we-do-not-speak-of and the red Caddy and the yellow Buick are still there!

[Todd138]

You could always just hook it up like a lawn mower seat and when your out of the seat it kills the fuel pump?

And hook up a switch to bypass the seat switch for when you have to leave it running when your working under the hood....

Which just means you would have to jump ship before an accident.....nevermind this is not a good idea

[Ken Heaton]

I drove by the-body-shop-who's-name-we-do-not-speak-of and the red Caddy and the yellow Buick are still there!

That does not surprise me, all things considered I am astonished that he actually got my vehicle done when he did!!:D

[CMS3900]

Alot of stationary military equipment is run this way. The hot to the fuel pump or diesel fuel cutoff solenoid relay is run from a oil pressure switch. In the case of military stuff you crank it until it builds oil pressure and then let the key go. If you let off the starter too soon it just dies. It sounds funny too, like your starting a car thats already running but it works. The downside to it is that the military equipment that had this was stationary so if it shut off it was just a pita. I would hate to think what it would be like on the highway and your a quart low and it shuts the truck off. For trucks and things they had a low oil buzzer so if you could find 2 different pressure value switches to buzzer first and shut off second it might be a idea.
Having the bypass switch would be nice. On the military stuff we called it a battle short switch. In case the sensor got fubared it would still run.

Hope this helped,
Morgan

[rvrsrvc]

I sent the inertia switch out on Wednesday. Did it make it to your desk?

[Ken Heaton]

I got the inertia switch yesterday, I wired it up last night, now all I have to do is mount it. I also have the relays ready to go, it was a struggle mounting the low oil pressure switch as the thread was different than the original OEM switch. I was able to mount it on a separate port on the oil filter housing that is bolted to the block.