After failing miserably to find anyone else who seems to have made an effort to stop their engine being lunched following loss of oil pressure - I had a go myself at a simple circuit - any comments - any pitfalls I've missed?


Oil press fuel+ign cutoff


[Edited on 15/4/04 by SteveF]

I haven't bothered following the diagram (cause i'm lazy) but .....

how do you start the engine as it won't have any oil pressure.

you will have no priming for the fuel pump, but that may not be a problem for you.
mike r, thats why he has put the diode in.
he will get a supply via the start position to the fuel pump and therefore the coil.

the other problem i see is that the diode is connected to the output of the solenoid therefore the main starter terminal, which while the engine is running will be supplied by the alternator, which means that with a loss of oil pressure the engine will still run because of the supply via the diode.

i think you should have connected the diode line to the starter switch output (ampage allowing).

Do what the racing boys do to protect their very expensive engines.
Use an exeptionally bright or large low O/P warning light in conjunction with a switch that gives you a "Low" but not a "very Low" warning that pressure is falling.
When light comes on and blinds you, stop engine, pull over, lift bonnet

Thanks for the feedback -

The pump is a facet solid state - so has no problem priming itself under normal circumstances - but one item I didn't show in the diagram is that I've also put in a 'prime button' under the bonnet which effectively just runs the fuel pump without anything else happening - so I can prime the system if its been stood for a long time

The line with the diode from the solenoid is connected to the output side of the solenoid i.e. the connection for the starter motor - so from my understanding this isn't live when the start button isn't pressed - at least that's what I've found when I've tested the circuit

BUT THE POSITIVE TERMINAL ON THE STARTER MOTOR WILL BE POWERED BY THE ALTERNATOR WHEN THE ENGINE IS RUNNING, THIS IS THE CABLE THAT CHARGES THE BATTERY.

If that was the case the starter motor would be energised all the time the engine was running - which isn't the case

My diagram doesn't show that there is another 'output' terminal on the solenoid - which is where all the other +ve feeds come from. The one from which I've taken the feed for the pump ONLY serves the starter motor

The diagram below shows a typical starter cicuit & solenoid with separate +ve feeds for the 'stock wiring' and starter - as mine has

quote:

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Originally posted by Fifer
Do what the racing boys do to protect their very expensive engines.
Use an exeptionally bright or large low O/P warning light in conjunction with a switch that gives you a "Low" but not a "very Low" warning that pressure is falling.
When light comes on and blinds you, stop engine, pull over, lift bonnet

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I invested £10 in a brand new oil pressure switch so hopefully it should be as reliable as any 'factory car' - never heard of one of those cutting out prematurely

Personally I'd be more worried about pulling out infront of a truck & locking the back end up due to the engine seizing - I reckon the pressure switch is more reliable than the oil containment on my Xflow

how about this from demon tweeks

normally there is a main battery feed cable to the stater motor(starter path) which is then connected to the alternator (charging path), the solenoid only allows the motor to operate, the power is always there on the main terminal, trust me, if not feel free to put a spanner across this terminal to the body of your car!!!!
unless im wrong this is the terminal you where going to connect to.
note i was only trying to help.

i think i have just realised the confusion, you mean the short cable (normally braided) between solenoid and starter.
if i had looked at you drawing properly i would have noticed first time. sorry.

Brooky - that's the sort of thing I have - but on a Tee with the oil pressure guage sender

Elite - finally we're on the same page (of the drawing ) - if its any consolation I may have to move the 'ignition relay' out of the main pump feed line, and put it in parallel with the pump rather than in series - as I'm only getting 11.5 v at the pump - which doesn't seem to be enough to run it

Ho-hum back to the drawing board ...

OK - final version - fitted and working
Note the use of a NC oil pressure switch rather than a NO - because that was the one I had (NO switch needed to come off a metro turbo - not held in stock at local motro factors)


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Agree with James et al. seems well dodgy to cut engine on low oil pressure. I intend to fit some type of buzzer (possible using same one I intend to use to remind me my indicator is on) - oil pressure drops buzzer goes off - drop revs, pull over at earliest possibility.

Speaking from experience of being in the outside lane of A52 in Mk 2 Golf when the very situation occurred - wouldn't have fancied being stucjk there in rush hour traffic.

I've got a buzzer on my indicators - can't hear it when I've got a helmet on - on track - which is probably the most likely time for something to blow - when it's being caned