[1986cj]

Ok I am trying to understand how the oil pressure kill switch works on a junk yard tbi set up. I have seen some good pictures on how to but I realy dont understand. For one I guess if you loose oil pressure it will kill the lead to the fuel pump but how does it know when you trun on the key on not started (you would have no oil pressure yet) how does it power the pump? I guess I am not realy good with the electronics but Jeephammer and I think John Streak (sorry if i butcherd your name) have had some great write ups on realys and now I understand the need and how they work. Realy very simple. So if you have any ideas that will help me to understand the kill swich Please chim in. Thanks

[JeepHammer]

John Strenk will surely have some good information on this, and I'd welcome his comments, images, ect. if he's got time to post up on this stuff!
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It depends on what you are trying to do...

FIRST,

The 'Low Oil Pressure' kill has to be overridden when you are trying to start the vehicle, or it will never start up...
OR,
You will have to 'Dry Crank' on the engine until the oil pressure comes up and activates the pressure switch.

SO!
You need an 'OverRide' circuit to make the system work seamlessly.
This circuit can be manual (a button you push while starting the vehicle) or you can wire it into the circuit...
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TWO.

All I've posted about are common 'Instant On, Instant Off' relays.
Latching relays, timed relays, delay relays, ect. I haven't written about because less than 1% of the readership would follow the conversation.

There is such a thing as a 'Timed Relay', in fuel systems, it's often called a '2 Second Relay'...

The idea is, when you turn the key switch to 'Start' or 'Crank' and the engine fires right up, the relay to the fuel pump will stay engaged 2 to 5 seconds to keep the engine running while the oil pressure comes up.

If the oil pressure DOESN'T come up in the allotted time frame, the relay opens, and the fuel pump stops getting power.

This is NOT to save your engine from low oil pressure, although it has that added bonus!

It's a safety switch to keep your fuel pump from running on if you have an accident or roll over, or anything else that would stop oil pressure.

In an accident where the key is left 'ON' the fuel pump would continue to deliver fuel even if the fuel lines were broken, or the fuel was on fire!
As long as there is battery current getting to the fuel pump, the pump could deliver fuel to a fire, or pour it on your face in an accident, And I'm SURE I wouldn't want that!

Have an accident and the engine dies, or roll over and the engine is starved for oil,
The 'Save Me' switch triggers and you don't get raw fuel being pumped anymore!
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THREE.

There are a couple of ways to wire a 'Save Me' switch, and depending on which 'Junk Yard' fuel injection set up you have, will determine which switch you will need...

What I normally use is a three terminal switch rated for around 10 PSI.

One terminal is NORMALLY CLOSED CIRCUIT TO GROUND, and that circuit opens when the oil pressure reaches 10 PSI.

Two terminals are NORMALLY OPEN, and the circuit CLOSES at about 10 PSI of oil pressure to transfer current to a relay or whatever...
They ARE NOT connected to ground in any way, so they are safe for power connections.



In this picture, the power comes into one side of the swtich, and when the oil pressure reaches about 10 PSI, the swtich closes the circuit, and directs the power up to my accessories relays,
That in turn powers up accessories, like air compressor, heater fan motor, stuff like that.

(Virtually all things in my jeep are powered from relays instead of directly though the switches, since the lower current required to trigger a relay means my switches will all last longer...)

The Unused terminal in this image now has an 'Idiot Light' attached to it so if I loose oil pressure, a buzzer and warning light go off on the dash to alert me there is a problem.

http://www.junkyardgenius.com/wiring/Images/idiotlights01.gif
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This might help you out for basic relay function, but DOES NOT cover latching relays (Relays that stay closed once activated)
And it doesn't cover timed/delay relays.

Timed relay is like the one used in most fuel injection systems,
Once the signal power is cut to the relay, the relay stays engaged a preset amount of time. With fuel injection systems, it's usually 2 to 5 seconds.

Delay Relays don't activate immediately when the signal power is applied.
They will take anywhere from 2 seconds to 5 minutes to activate.
They are commonly used in applications where things have to sequence on start up.
Like activation pressure pumps before spray nozzles activate,
Or in automotive applications, allowing the oil pressure to come up before the 'Safety Switch' activates.

Anyway, here are some relay basics.



And this will tell you about some of the common relays available for high drain electrical appliances,



Publish pictures of your relay(s) and give close ups of the schematics on the relays and I'll decipher your wiring for you and post diagrams when I get time...