Oil pressure switch based ignition cut out

[Vertigo]

Hiya. Thinking about doing this. Seems like a relay triggered by an aftermarket oil pressure switch would work, but then I realized that there is no oil pressure when the engine isnt running. But there should be at least some during cranking - would it be enough? This is a 4AGZE that produces about 30-50psi when running cold, about 10-20psi when running hot. Id like it set to cut out when pressure drops below 5psi.

[tortron]

Vn/vp Commodores had this set up. (But poorly executed)

The oil pressure switch is in the fuel pump circuit, the idea being that if the car rolls the no oil pressure will cut off the fuel.

The ign on position also runs the fuel pump so you can prime the system to start and is tied into the ECU. It seems most of them weren't wired correctly from factory, but it works on paper/the wiring diagram

 

[tortron]

An improvement may be to have the fuel pump relay to operate on a 20 second? Timer when ign is switched to on. And then the oil pressure circuit can take over while the engine is running

[M.H.]

Does the ECU not turn on the fuel pump? If it does then if the engine stalls the fuel pump will stop

[Vertigo]

Id prefer it to be an ignition cut, as its more immediate. Its more about preventing as much engine damage a possible, than anything else.

[tortron]

Same deal then, have the oil pressure switch earth the ign. Timer relay to get it going (could even run that off the door light circuit)3

[M.H.]

Just now, Vertigo said:

Id prefer it to be an ignition cut, as its more immediate. Its more about preventing as much engine damage a possible, than anything else.

Why bother, just have a warning buzzer/light for low pressure. Last thing you want is the engine being cut out mid corner

[cletus]

15 minutes ago, Vertigo said:

Hiya. Thinking about doing this. Seems like a relay triggered by an aftermarket oil pressure switch would work, but then I realized that there is no oil pressure when the engine isnt running. But there should be at least some during cranking - would it be enough? This is a 4AGZE that produces about 30-50psi when running cold, about 10-20psi when running hot. Id like it set to cut out when pressure drops below 5psi.

would it be any real advantage if it doesn't take RPM into consideration?  ie if its doing 7000rpm, and its got 7psi oil pressure for some reason, its not going to cut out, and its still going to get damaged?

 

[mfordy]

I use a bypass switch for startup.

[kpr]

If engine has no oil pressure its generally broken already.   but if running on an aftermarket ecu i'd be using that to control it via a pressure sensor

[Yowzer]

Yup, with a decent after market ECU you can map pressure against RPM / temp etc and get a warning when it drops out of normal range, hopefully before it is catastrophically low. You could also build a standalone device, Arduino based perhaps, to do the same thing. Is this a track car, or just a road car? If a track car, you're going to be hard pressed to catch an oil pressure issue before it causes damage, unless it's simply temperature related. Prevention is better in this case, make sure your oil pump is up to the task, you have an oil cooler with secure lines, engine can return the oil to the sump fast enough, and you have a suitable oil grade to begin with. If it's just a road car, just ensure everything is well maintained and you're going to be fine. A buzzer hooked to the lamp circuit would be better, after all you still have to chop the engine out of drive anyway. 

10-20psi hot, is that at idle? Coz that seems pretty low already.

[M_C]

Perhaps an Accusump may work better?

link it into a warning/shutdown if it is triggered?

I managed to kill the Escort engine on the Hampton sweeper with lack of oil and a mate did the same thing, same corner, same day. To be fair mine probably had more to do my lack of talent flogging and old inappropriate engine (the mighty Essex V6) while he lost a sump baffle trapdoor. I didn’t even notice my BIG red LED oil warning light on the dash. Expensive day and double shuffle on my trailer to get both cars home.

https://www.merlinmotorsport.co.uk/knowledge_base_articles/view/accusump-oil-accumulators-how-do-they-work-281
https://cardwells.co.nz/oil-systems-2/accusumps/canton-accusump.html

 

[RUNAMUCK]

You can buy relays that go open circuit when energized. 

So just wire one of those in off the oil light sender.

[Vertigo]

On 27/04/2020 at 02:27, Yowzer said:

10-20psi hot, is that at idle? Coz that seems pretty low already.

Yea, at idle. With revs it goes up to 40's or so. Heard its fine for a 4AGE. Also, running a turbo on it with no restricter, and Im reading the pressure at the oil filter after a relocation. I should move it to the stock location on the side of the block, tbh.

Heres what the service manual states.