Hi All,

I am currently in the process of wiring my car and it occurred to me that it would be a good idea if the petrol pump only ran when the engine was running. So if the engine ran low on oil pressure the fuel pump would stop and the engine would stop as a form of protection. Has anyone heard of this solution before? Is it a viable solution? A normal oil pressure switch goes open circuit when the pressure builds which is the opposite to what is required. Can you get a pressure switch that works the other way around to standard? I understand that a separate switch to be able to bypass this mechanism may be required to prime the system.

Has anyone any thoughts on this suggestion?

Regards

Paul

Hi there,
Just a thought at the moment, maybe a relay in series with the switch power, that opens when the pressure drops, say below 10psi.

Not sure if this is feasible though.
I'll think on it a little and if I come up with something I will let you know.

Good Luck RobG.

Hi Robert, Thanks for the feedback. I was thinking of a couple of solutions:
1) using a brake light switch as these are normal open circuit until the pressure rises. So when the engine is running then there would be power to the circuit like pressing the brake pedal which would provide power to the fuel pump. The problem is the pressure needed to operate the switch is unknown, so the oil pressure may not be enough.

2) Using a relay that is normally closed circuit until there is power to it. This would mean that a normal pressure switch could be used like the oil warning light which comes on below about 5 PSI.....Above 5 psi there would be no power so the relay would revert to the normally closed position and if the pressure dropped below 5 psi there would be power which would switch the relay to the open circuit position.

I was told that there was something like this on some MGs but I haven't managed to find anything yet. I can't believe this is the first time this has been thought of as it seems like a logical way of protecting the engine should something go wrong oil pressure wise.

Sounds like overkill to me but then I love old cars for thier simplicity and the requirement of being in tune!
You would require two relays, one switched by the oil ppressure switch (1) and one switched by the cranking/starter (2)
Ignition feed through normally closed relay 1 in parallel with normally open relay two. If required I can email a drawing to you.

Hi Steve, I believe this system was fitted to SD1 and the old original Range Rover. It would be overkill if the system was like some of the Audis that work off of cam belt tension and a host of CPUs to support it. I strongly believe in keeping things as simple as possible but this seemed like a simple neat solution that could protect the engine and save an awful lots of money if something went wrong.

Regards

Paul

Hi Paul - strikes me as being a bit paranoid.
Oil pressure warning light and a pair of eyes would do for most people.
Also there may be occasions where you would need to risk driving on to a place of safety. I wouldn't fancy an instantaneous fuel cut-off while tanking it up the outside lane of a motorway(way to scary for me thanks !!)
regards - Chris

Hi Chris, An interesting and seat gripping scenarion you have painted there. Hadn't thought of it in those terms so definately food for thought. Would be a scary situation while travelling at the maximum legal limit in the outside lane and the oil light comes on. A risk either way and definately buttock clenching. Thanks to all for their thoughts. This system was fitted to Range Rovers and SD1's I believe. Regards Paul

Hi everyone who has posted on this subject.

After reading all the previous posts I think the route I favour is to see if it is possible to have the oil pressure light come on at slightly higher (10/15) psi and fit a separate manual OFF Switch to the fuel pump (perhaps with a "Doomsday Cover") so it cannot be accidently operated.

Cheers Rob