SteveF
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| posted on 15/4/04 at 07:09 PM |
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Wiring for low oil press ignition / fuel pump cutout
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]
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MikeR
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| posted on 15/4/04 at 09:15 PM |
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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.
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elitewiring
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| posted on 15/4/04 at 09:23 PM |
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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.
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elitewiring
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| posted on 15/4/04 at 09:25 PM |
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i think you should have connected the diode line to the starter switch output (ampage allowing).
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Fifer
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| posted on 16/4/04 at 08:00 AM |
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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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SteveF
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| posted on 16/4/04 at 11:13 AM |
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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
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elitewiring
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| posted on 19/4/04 at 02:00 PM |
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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.
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SteveF
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| posted on 19/4/04 at 03:16 PM |
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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
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James
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| posted on 19/4/04 at 04:31 PM |
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quote:
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
I agree- even Hicost (who's engines cost about 10K) doesn't have a cutout- just a large orange light- tagged as 'Game Over'!
Also, if your oil pressure sensor gets a bit dicky then your engine will keep cutting out- potentially at dangerous times like pulling out in front of
a truck! 
Sorry to put a downer on your hard work!
James
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SteveF
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| posted on 19/4/04 at 05:44 PM |
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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 
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Brooky
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| posted on 19/4/04 at 08:59 PM |
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how about this
from demon
tweeks
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elitewiring
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| posted on 19/4/04 at 09:12 PM |
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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.
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elitewiring
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| posted on 19/4/04 at 09:15 PM |
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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.
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SteveF
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 posted on 19/4/04 at 10:09 PM |
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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 ...
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SteveF
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| posted on 21/4/04 at 10:25 AM |
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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)
[img][/img]
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rayroni
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| posted on 21/4/04 at 11:55 AM |
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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.
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SteveF
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| posted on 23/4/04 at 08:42 AM |
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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
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